This article covers feeders and branch circuits located outside on premises between buildings or poles, or for equipment on the outside of buildings or poles.
Table 225.2 refers to other articles in the Code which are pertinent to outside branch circuits and feeders.
| Branch Circuits | 210 |
| Class 1, Class 2, and Class 3 Remote-Control, Signaling, and Power-Limited Circuits | 725 |
| Communications Circuits | 800 |
| Community Antenna Television and Radio Distribution Systems | 820 |
| Conductors for General Wiring | 310 |
| Electrically Driven or Controlled Irrigation Machines | 675 |
| Electric Signs and Outline Lighting | 600 |
| Feeders | 215 |
| Fire Alarm Systems | 760 |
| Fixed Outdoor Electric De-icing and Snow-Melting Equipment | 426 |
| Floating Buildings | 553 |
| Grounding | 250 |
| Hazardous (Classified) Locations | 500 |
| Hazardous (Classified) Locations, Specific | 510 |
| Marinas and Boatyards | 555 |
| Messenger Supported Wiring | 396 |
| Mobile Homes, Manufactured Homes, and Mobile Home Parks | 550 |
| Open Wiring on Insulators | 398 |
| Over 600 Volts, General | 490 |
| Overcurrent Protection | 240 |
| Radio and Television Equipment | 810 |
| Services | 230 |
| Solar Photovoltaic Systems | 690 |
| Swimming Pools, Fountains, and Similar Installations | 680 |
| Use and Identification of Grounded Conductors | 200 |
I. General
| 225.3 | Calculation of Loads 600 Volts, Nominal, or Less |
Use 210.10 for outdoor branch circuits and Part III of Article 220 for outdoor feeders.
Conductors must be insulated or covered within 3 m (10 ft.) of a building. Conductors in raceways or cables except MI must have thermoplastic or rubber insulation. An exception is made for equipment grounding conductors and grounded circuit conductors. Section 310.8 governs wet locations.
| 225.5 | Size of Conductors 600 Volts, Nominal, or Less |
Size in accordance with Section 310.15. Determine loads in accordance with Section 220.10 and Part III of Article 220.
| 225.6 | Conductor Size and Support |
(A) Overhead Spans
600 V or less, up to 15 m (50 ft.): 10 AWG copper, 8 AWG aluminum except where supported by a messenger wire
600 V or less, over 15 m (50 ft.): 8 AWG copper, 6 AWG aluminum except where supported by a messenger wire
More than 600 V: 6 AWG copper, 4 AWG aluminum for open conductors; 8 AWG copper, 6 AWG aluminum for cable
(B) Festoon Lighting
Use 12 AWG or Larger for festoon lighting except where messenger wires support them, over 12 m (40-ft.) span require messenger wire support.
| 225.7 | Lighting Equipment Installed Outdoors |
| 225.10 | Wiring on Buildings |
| 225.11 | Circuit Exits and Entrances |
Refer to Sections 230.52, and 230.54.
| 225.12 | Open Conductor Supports |
| 225.14 | Open Conductor Spacings |
| 225.15 | Supports Over Buildings |
Refer to Section 230.29.
| 225.16 | Attachment to Buildings |
Refer to Sections 230.26 and 230.27.
| 225.17 | Masts as Supports |
| 225.18 | Clearance from Ground |
Open conductors and open multiconductor cables not over 600 V must conform to the following:
3 m (10 ft.): above finished grade: 150 V to ground
3.7 m (12 ft.): over residential driveways and commercial areas not subject to truck traffic: 300 V to ground limitation
4.5 m (15 ft.): same as 3.7 m (12 ft.) above: exceeding 300 V to ground
5.5 m (18 ft.): above streets, driveways, etc. subject to truck traffic as well as land used by vehicles such as forest, grazing, etc.
| 225.19 | Clearances from Buildings for Conductors of Not over 600 Volts, Nominal |
(A) Above Roofs. Not less than 2.5 m (8 ft.) vertical clearance from the roof surface maintained for a distance of not less than 900 mm (3 ft.) in all directions from the edge of the roof except the final span to the attachment to the building. If subject to pedestrian or vehicular traffic, vertical clearances should be in accordance with Section 225.18. Other exceptions are as follows:
900 mm (3 ft.) clearance: voltage between conductors not more than 300 V and roof slope is maximum of 100 mm (4 in.) in 300 mm (12 in.).
450 mm (18 in) clearance above the overhanging portion of the roof: voltage between conductors not more than 300 V, not more than 1.8 m (6 ft.) of conductor, 1.2 m (4 ft.) horizontally, do not pass over an overhang and are terminated in approved support or raceway through the roof.
900 mm (3 ft.) clearance does not apply to the final conductor span attached to the roof.
(B) From Nonbuilding or Nonbridge Structures. Clearances in all directions to be a minimum of 900 mm (3 ft.).
(C) Horizontal Clearances. Not less than 900 mm (3 ft.).
(D) Final Spans. Those may be attached to a building but must clear operable windows, fire escapes, and the like by at least 900 mm (3 ft.). If above the top level of a window then it can be reduced to less than 900 mm (3 ft.). There is additional information concerning openings in commercial buildings and vertical clearances.
(E) Zone for Fire Ladders. Allow for fire laddersat least a 1.8 m (6-ft.)-wide space.
| 225.20 | Mechanical Protection of Conductors |
Refer to Section 230.50.
| 225.21 | Multiconductor Cables on Exterior Surfaces of Buildings |
Refer to Section 230.51.
| 225.22 | Raceways on Exterior Surfaces of Buildings, or Other Structures |
They must drain and be raintight in wet locations other than flexible metal conduit as permitted in 348.12(1).
| 225.24 | Outdoor Lampholders |
| 225.25 | Location of Outdoor Lampholders |
| 225.26 | Vegetation as Support |
Not permitted.
II. More Than One Building or Other Source
| 225.30 | Number of Supplies |
Where you have more than one building under one management and on the same property you can only have one feeder or branch circuit from the service disconnect supplying each of the additional buildings. The exceptions are noted in (A) through (E).
(A) Special Conditions. You can have additional feeders or branch circuits for fire pumps, emergency systems, legally required standby systems, parallel power production systems, optional standby systems, and systems connected to multiple sources of supply for greater reliability.
(B) Special Occupancies. In a single building where the load is too large for one feeder or branch circuit or in multi-occupancy buildings where there is no space for supplies accessible to all occupants then with special permission you can have additional feeders or branch circuits.
(C) Capacity Requirements. If the load requirements are more than 2000 A and the voltage is not more than 600 V, more than one supply is allowed.
(D) Different Characteristics. More than one supply is allowed if different characteristics, i.e., voltage, frequency, etc. are required.
(E) Documented Switch Procedures. You can have more than one supply if they are under one management and there are documented safe disconnecting procedures.
| 225.31 | Disconnecting Means |
Must be provided.
It must be located at the poiint where the wire passes through the building either inside or outside. It must be readily accessible. You are allowed to use the requirements of Section 230.6. There are four exceptions.
| 225.33 | Maximum Number of Disconnects |
The provision for disconnecting each supply in 225.30 can consist of no more than six switches or six circuit breakers. Single-pole units can be used on multiwire circuits, one pole for each ungrounded conductor. They must be tied together as a multipole disconnect and will then be counted as one disconnect. An exception is made for the control circuit of a ground-fault protection system or the control circuit of the power operated supply disconnecting means.
| 225.34 | Grouping of Disconnects |
All disconnects are to be grouped together. An exception is made for fire pumps. The disconnects for fire pumps, emergency legally required standby or optional standby systems must be located away from the normal supply.
| 225.35 | Access to Occupants |
Must be accessible to the occupants except where there is a single management with continuous supervision.
| 225.36 | Suitable for Service Equipment |
| 225.37 | Identification |
| 225.38 | Disconnect Construction |
| 225.39 | Rating of Disconnect |
In general, the feeder or branch circuit disconnect must be sized to carry the calculated load as determined in accordance with Article 220. There are special cases where a minimum size is required. They are:
15 A: a single branch-circuit load.
30 A: up to two, two-wire branch circuits
100 A: three-wire: one-family dwelling with six or more two-wire branch circuits or calculated load is 10 kW or more.
60 A: all others.
| 225.40 | Access to Overcurrent Protective Devices |
III. Over 600 Volts
| 225.50 | Sizing of Conductors |
| 225.51 | Isolating Switches |
| 225.52 | Locations |
| 225.53 | Type |
| 225.60 | Clearances over Roadways, Walkways, Rail, Water, and Open Land |
| 225.61 | Clearances over Buildings and Other Structures |
Page 2
This article describes requirements for service conductors and equipment for control and protection of services. Figure 230.1 describes where in Article 230 different parts of the service are described.
I. General
A building normally can have only one service. If more than one is permitted as a result of the exceptions provided, then a directory of all services must be placed at each service. For the purposes of Section 230.40, Exception 2, underground conductors sized at least 1/0 are considered one service if they are connected at the supply but not at the load. More than one service is permitted as follows:
(A) Special Conditions
(1) Fire pumps if required.
(2) Emergency systems.
(3) Legally required standby systems.
(4) Optional standby systems.
(5) Parallel power production systems.
(6) Systems designed to connect to multiple sources of supply for enhanced reliability.
(B) Special Occupancies
(1) In multiple-occupancy buildings where there is no room for each tenant to have access to the service equipment, with permission, more than one set of service conductors can be tapped from one service drop or service lateral.
(2) If a single building is too large then with special permission, more than one service may be installed.
(C) Capacity Requirements
(1) If the capacity requirements are larger than 2000 amperes at 600 volts or less.
(2) If a single-phase installation were larger than the utility would normally serve through one service.
(3) With special permission.
(D) Different Characteristics
More than one service is permitted if there are different rate schedules, voltages, phases, frequencies or uses.
(E) Identification
If a building is supplied by more than one service, feeder, or set of branch circuits, a permanent directory or plaque has to be installed at the disconnect location.
| 230.3 | One Building or Other Structure Not to Be Supplied through Another |
Service conductors cannot pass through another building.
| 230.6 | Conductors Considered Outside of Building |
If conductors have a cover of at least 50 mm (2 in.) of concrete under a building or are installed in a raceway encased in at least 50 mm (2 in.) of concrete or are installed in a vault as per Article 450 Part III, or installed in concrete and under at least 450 mm (18 inches) of earth under a building they are treated as being outside the building.
| 230.7 | Other Conductors in Raceway or Cable |
| 230.8 | Raceway Seal |
| 230.9 | Clearance from Building Openings |
If installed as open conductors or multiconductor cable without an outer jacket, clearance of at least 900 mm (3 ft.) is required from operable windows, doors, porches, fire escapes, stairs, ladders, balconies, and the like. There is an exception for conductors above the top level of a window. Overhead service conductors are not permitted underneath openings through which materials can be moved or obstructing these openings. Vertical clearances under certain conditions are to be maintained in accordance with Section 230.24(B).
| 230.10 | Vegetation as Support Not Permitted |
II. Overhead ServiceDrop Conductors
| 230.22 | Insulation or Covering |
Insulation or covering is required on individual conductors.
Conductors should have the capacity required for the load in accordance with Article 220 and have enough mechanical strength. The minimum size should be 8 AWG copper or 6 AWG aluminum or copper-clad aluminum. Grounded conductors shall be as required in Section 250.24(B). There is an exception.
Service-drop conductors must not be accessible and comply with the following:
(A) 2.5 m (8 ft.) vertical clearance maintained above the roof with 900 mm (3 ft.) from the edge of the roof is generally the clearance required above roofs with a nominal voltage of 600 V except where the service drop is attached to the side of the building. This is reduced to 900 mm (3 ft.) with a voltage of 300 V and a roof slope of 100 mm (4 in.) in 300 mm (12 in.) or more. It is also reduced to 450 mm (18 in.) above the overhanging portion with a nominal voltage of 300 V if only up to 1.8 m (6 ft.) of service drop conductors, 1.2 m (4 ft.) horizontally, pass over the roof and the conductors end on a support or raceway. Where there is traffic above a roof surface use requirements of Section 230.24(B).
(B) The clearances above the ground vary for conductors with a nominal voltage of 600 V. They are:
3.0 m (10 ft.): voltage of 150 V to ground, service entrance to buildings accessible to pedestrians.
3.7 m (12 ft.): over residential property and no truck traffic commercial areas with voltage to ground not in excess of 300.
4.5 m (15 ft.): at areas listed in 3.7 m (12 ft.) classification when the voltage exceeds 300 V to ground.
5.5 m (18 ft.): over public streets. Private property is included if traveled with commercial vehicles.
(C) Refer to Section 230.9 for clearances from building openings.
(D) Refer to Section 680.8 for clearances from swimming pools.
| 230.26 | Point of Attachment |
A minimum clearance of 3.0 m (10 ft.) is required. Compliance with 230.9 and 230.24 is required.
| 230.27 | Means of Attachment |
| 230.28 | Service Masts as Support |
| 230.29 | Supports over Buildings |
III. Underground ServiceLateral Conductors
Generally, they are insulated with the voltage determining the insulation. There are some exceptions for grounded conductors of bare wire and aluminum or copper-clad aluminum cable assemblies.
The conductors must be large enough to carry the load in accordance with Article 220. No smaller than 8 AWG for copper and 6 AWG for aluminum or copper-clad aluminum. An exception is made where the service supplies only a single load on a single branch circuit. The grounded conductor must not be sized less than required in Section 250.24(B).
| 230.32 | Protection against Damage |
| 230.33 | Spliced Conductors |
IV. Service-Entrance Conductors
| 230.40 | Number of Service-Entrance Conductor Sets |
Generally, a service drop or lateral can only supply one set of service conductors. However, one set of service conductors can supply each occupancy or a group of occupancies in a multiple- occupancy building. A second exception for separate enclosures is noted. A third exception is noted for single family or a separate structure. There are two additional exceptions.
| 230.41 | Insulation of Service-Entrance Conductors |
Generally, if the conductors are on or enter a building, they should be insulated. Exceptions are made for grounded conductors of bare copper wire and aluminum, copper-clad aluminum cable assemblies in special cases, copper for direct burial where the copper is all right for the soil, and aluminum or copper-clad aluminum part of an assembly rated for direct burial.
| 230.42 | Minimum Size and Rating |
(A) General. The ampacity of the conductors is to be either the sum of the noncontinuous load and 125% of the continuous load or the sum of the noncontinuous and continuous loads if the overcurrent devices are rated for operation at 100% of their rating. The loads are calculated in accordance with Article 220. The ratings are determined in accordance with Section 310.15. For busways use the listing or rating of the busway.
(B) Ungrounded Conductors. Use at least the rating of the disconnecting means as specified in Section 230.79(A) through (D).
(C) Grounded Conductors. Size in accordance with Section 250.24(B).
| 230.43 | Wiring Methods for 600 Volts, Nominal, or Less |
Only the following methods are permitted: Open wiring on insulators; type IGS cable; rigid metal conduit; intermediate metal conduit; EMT; ENT; service entrance cables; wireways; busways; auxiliary gutters; rigid NMC; cablebus; MC cable; mineral-insulated, metal-sheathed cable; flexible metal conduit or liquidtight flexible metal conduit with certain restrictions; or liquidtight flexible nonmetallic conduit.
To support cables, a cable tray system may be used.
| 230.46 | Spliced Conductors |
| 230.49 | Protection against DamageUnderground |
| 230.50 | Protection of Open Conductors and Cables against DamageAbove Ground |
| 230.51 | Mounting Supports |
| 230.52 | Individual Conductors Entering Buildings or Other Structures |
| 230.53 | Raceways to Drain |
| 230.54 | Overhead Service Locations |
Connections to the service drop conductors have to be made raintight with a raintight head or with a gooseneck. The heads or goosenecks must be above the point where the conductors are attached to the building and must be securely attached. Drip loops must be constructed to prevent entrance of moisture. There are other requirements.
| 230.56 | Service Conductor with the Higher Voltage to Ground |
V. Service EquipmentGeneral
| 230.62 | Service EquipmentEnclosed or Guarded |
Energized parts must be enclosed so that no one can make accidental contact or guarded. If energized parts are not enclosed then they must be guarded as noted in 110.18 and 110.27. If the energized parts are guarded in accordance with 110.27(A)(1), then there has to be a provision for locking or sealing the doors.
Service equipment must be marked for use as service equipment.
VI. Service EquipmentDisconnecting Means
There must be a way to disconnect all conductors in the building from the service-entrance conductors. The disconnect must be readily accessible either outside the building or inside the building nearest the point of entrance of the service conductors. It must have proper markings and be suitable for its use. Service disconnects cannot be installed in bathrooms. If a remote control device is used to actuate the service disconnect then the service disconnect must still be at a readily accessible location. The service disconnecting means must be suitable for the conditions where it is installed. Refer to Articles 500 through 517 for hazardous locations.
| 230.71 | Maximum Number of Disconnects |
The provision for disconnecting each service (Section 230.2) or the service entrance conductors (Section 230.40, Exception Nos. 1, 3, 4, or 5) can consist of no more than six switches or six circuit breakers or combinations. Single-pole units can be used for multiwire circuits, one pole for each ungrounded conductor. They must be tied together as a multipole disconnect and will then be counted as one disconnect. An exception is made for the control circuit of a ground-fault protection system, power monitoring equipment, transient voltage surge suppression, or power-operable service disconnecting means.
| 230.72 | Grouping of Disconnects |
All disconnects are to be grouped together. There is an exception for a disconnect used for a water pump for fire protection. If there are additional services as permitted in 230.2 for emergency systems, legally required standby or operational standby systems, or fire pumps, then the disconnecting means must be installed away from the normal service disconnecting means so that the possibility of interrupting the services at the same time is reduced. Where multiple occupancies are present, each occupant must have access to his or her own disconnect. There is an exception to this latter requirement for certain management conditions.
| 230.74 | Simultaneous Openings of Poles |
| 230.75 | Disconnection of Grounded Conductor |
| 230.76 | Manually or Power Operable |
| 230.77 | Indicating |
| 230.79 | Rating of Disconnect |
In general, the service disconnect must be sized to carry the calculated load. There are special cases where a minimum size is required. They are:
15 A: a single branch-circuit load
30 A: up to two, two-wire branch circuits
100 A: three-wire: one-family dwelling
60 A: all other cases
| 230.80 | Combined Ratings of Disconnects |
If more than one service switch is used, their combined rating must be at least the rating shown in Section 230.79.
| 230.81 | Connection to Terminals |
| 230.82 | Equipment Connected to the Supply Side of Service Disconnect |
Among the pieces of equipment allowed to be connected to the supply side of a service switch are: current-limiting devices, meters, instrument transformers, surge protective devices, fire and sprinkler alarms, fire pump equipment, and interconnected electric production sources. Some of these items require separate protection and disconnects. Refer to the NEC® for a complete description and list.
VII. Service EquipmentOvercurrent Protection
(A) Every ungrounded conductor must have an overcurrent device. It must normally not be set higher than the rating of the conductors. There are five exceptions to this and they include: motor starting current; fuses and circuit breakers conforming to Section 240.3(B) or (C) and Section 240.6; six fuses or circuit breakers is the limit for consideration as a service overcurrent device; fire pumps under certain conditions; when permitted by Section 310.15(B)(6) for 120/240 volt, three-wire, single-phase dwelling services.
(B) No overcurrent device is to be placed in a grounded conductor.
The service overcurrent device must be part of the service disconnect or be next to it.
| 230.92 | Locked Service Overcurrent Devices |
| 230.93 | Protection of Specific Circuits |
| 230.94 | Relative Location of Overcurrent Devices and Other Service Equipment |
Some of the items allowed ahead of the overcurrent device are: service switch, surge protectors, protective signaling systems, fire pump, meters, and power-operable service equipment controls.
| 230.95 | Ground-Fault Protection of Equipment |
This is required for all services that are 150 V to ground up to 600 V phase to phase, solidly grounded wye, with service switches 1000 A or more. The grounded conductor must be connected directly to ground. No impedance device is allowed. The rest of this section contains information about the setting of these devices, the use of switches and fuses, and performance testing. An exception is allowed for continuous industrial processes where a nonorderly shutdown would be hazardous and for fire pumps. Refer to 517.17(A) for hospitals or other buildings with critical areas or life support equipment.
VIII. Services Exceeding 600 Volts, Nominal
| 230.200 | General |
| 230.202 | Service-Entrance Conductors |
| 230.204 | Isolating Switches |
| 230.205 | Disconnecting Means |
| 230.206 | Overcurrent Devices as Disconnecting Means |
| 230.208 | Protection Requirements |
| 230.209 | Surge Arresters (Lightning Arresters) |
| 230.210 | Service EquipmentGeneral Provisions |
| 230.211 | Metal-Enclosed Switchgear |
| 230.212 | Services over 35,000 Volts |
Page 3
I. General
Parts I through VII give requirements for circuits of up to 600 V. Part VIII covers supervised industrial installations up to 600 V. Part IX covers over 600 V.
| 240.2 | Definitions |
| 240.3 | Other Articles |
Table 240.3 refers to other articles in the Code which pertain to overcurrent profection for specific equipment and systems.
| Air-Conditioning and Refrigerating Equipment | 440 |
| Appliances | 422 |
| Audio Signal Processing Amplification, and Reproduction Equipment | 640 |
| Branch Circuits | 210 |
| Busways | 368 |
| Capacitors | 460 |
| Class 1, Class 2, and Class 3 Remote-Control, | 725 |
| Signaling, and Power-Limited Circuits Closed-Loop and Programmed Power Distribution System | 780 |
| Cranes and Hoists | 610 |
| Electric Signs and Outline Lighting | 600 |
| Electric Welders | 630 |
| Electrolytic Cells | 668 |
| Elevators, Dumbwaiters, Escalators, Moving Walks, Wheel Chair Lifts, and Stairway Chair Lifts | 620 |
| Emergency Systems | 700 |
| Fire Alarm Signaling Systems | 760 |
| Fire Pumps | 695 |
| Fixed Electric Heating Equipment for Pipelines and Vessels | 427 |
| Fixed Electric Space Heating Equipment | 424 |
| Fixed Outdoor Electric De-icing and Snow-Melting Equipment | 426 |
| Generators | 445 |
| Health Care Facilities | 517 |
| Induction and Dielectric Heating Equipment | 665 |
| Industrial Machinery | 670 |
| Luminaires (lighting fixtures), Lampholders, and Lamps | 410 |
| Motion Picture and Television Studios and Similar Locations | 530 |
| Motors, Motor Circuits, and Controllers | 430 |
| Phase Converters | 455 |
| Pipe Organs | 650 |
| Places of Assembly | 518 |
| Services | 230 |
| Solar Photovoltaic Systems | 690 |
| Switchboards and Panelboards | 408 |
| Theaters, Audience Areas of Motion Picture and Television Studios, and Similar Locations | 520 |
| Transformers and Transformer Vaults | 450 |
| X-Ray Equipment | 660 |
| 240.4 | Protection of Conductors |
For other than flexible cords and fixture wires, use ampacities specified in Section 310.15 when calculating overcurrent protection. There are a number of cases where this rule does not necessarily hold true with special requirements. Some of them are: power loss hazard; devices rated 800 amperes or less; devices rated over 800 amperes; tap conductors; motor-operated appliance circuit conductors; motor and motor control circuit conductors; phase converter supply conductors; air conditioning and refrigeration equipment circuit conductors; transformer secondary conductors; capacitor circuit conductors; electric welder circuit conductors; remote control signalling and power limited circuit conductors; and fire protective alarm system circuit conductors. Refer to the NEC® for a complete list and for other sections and articles that may be relevant.
| 240.5 | Protection of Flexible Cords, Flexible Cables, and Fixture Wires |
| 240.6 | Standard Ampere Ratings |
The standard ratings for fuses and inverse time circuit breakers are: 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600, 2000, 2500, 3000, 4000, 5000, and 6000 A. Fuses are also rated at 1, 3, 6, 10, and 601 A. There is a requirement for circuit breakers having external adjustable means and for restricted access adjustable trip circuit breakers.
| 240.8 | Fuses or Circuit Breakers in Parallel |
| 240.9 | Thermal Devices |
| 240.10 | Supplementary Overcurrent Protection |
| 240.12 | Electrical System Coordination |
If an orderly shutdown is required to reduce hazards to equipment and personnel, the following method can be used; coordinated short-circuit protection and/or overload indication.
| 240.13 | Ground-Fault Protection of Equipment |
For solidly grounded wye systems that are more than 150 V to ground and not exceeding 600 V phase to phase, ground-fault protection of equipment must be provided for each main disconnecting means rated 1000 A or more, in accordance with Section 230.95. The three exceptions are where an orderly shutdown in an industrial process is required, for fire pumps, and if the disconnect is protected by service ground-fault protection.
II. Location
| 240.20 | Ungrounded Conductors |
An overcurrent device (fuse or circuit breaker) has to be connected in series with each ungrounded conductor. An overcurrent relay with a current transformer is allowed. Generally, a circuit breaker has to open all ungrounded conductors. Single-pole circuit breakers are permitted under certain conditions listed in this section. In a closed-loop power distribution system, listed devices can be used instead of fuses or circuit breakers.
| 240.21 | Location in Circuit |
This section lists the location of the overcurrent device in relation to the ungrounded circuit conductor.
(A) Branch-Circuit Conductors. If a branch-circuit tap meets the requirements of Section 210.19, then the overcurrent protection can be located in accordance with that Section.
(B) Feeder Taps. Taps can be made at conductors without overcurrent protection at the tap as noted in section 240.21(B)(1) through (5) below. The provisions of 240.4(B) cannot be applied for tap conductors.
(1) Taps Not over 3 m (10 Feet) Long. They may be tapped to a feeder or transformer secondary without overcurrent protection when the tap is not longer than 3 m (10 ft.); the rating of the tap conductor is not less than the loads and devices it supplies and the overcurrent device at the end of the tap; the tap ends at the device it supplies; the tap conductors are enclosed in a raceway, and for field installations where the tap leaves the enclosure of the tap the rating of the overcurrent device on the line side of the tap is not more than 10 times the ampacity of the conductors.
(2) Taps Not over 7.5 m (25 Feet) Long. When the tap is not longer than 7.5 m (25 ft.) it does not require protection if the ampacity of the tap is at least one-third the rating of the feeder or overcurrent protection it was tapped from; ends in a single overcurrent device rated for the device; and is protected from physical damage by an approved method.
(3) Taps Supplying a Transformer [Primary Plus Secondary Not over 7.5 m (25 Feet) Long]. The rule is similar to the 7.5 m (25 ft.) tap (item c above). No overcurrent protection is required for a tap for a feeder supplying a transformer if the ampacity of the primary wires is at least one-third the rating of the overcurrent device protecting the feeder; when you multiply the rating of the conductors supplying the secondary by the ratio of the secondary to primary voltage it should be at least one-third the feeder protective overcurrent device rating; if both primary and secondary wires are not longer than 7.5 m (25 ft.) combined; the primary and secondary conductors are protected in an approved way from physical damage; and the secondary conductors end in a single overcurrent device limiting the load current to that permitted by Section 310.15.
(4) Taps over 7.5 m (25 Feet) Long. No overcurrent protection is required for a tap located in manufacturing installations with bays over 11 m (35 ft.) in height if the horizontal length is not longer than 7.5 m (25 ft.) with the overall length not longer than 30 m (100 ft.). All the rules of the tap not over 7.5 m (25 ft.) tap rule (2 above) apply, and in addition, the tap conductors must be at least 6 AWG copper or 4 AWG aluminum; they can not go through floors, walls, or ceilings; the tap must be least 9 m (30 ft.) from the floor; the tap conductors have no splices and are continuous from one end to the other and only qualified persons service the system.
(5) Outside Taps of Unlimited Length
(C) Transformer Secondary Conductors. There is a complete discussion of transformer taps. Among the items discussed are protection by primary overcurrent device, transformer secondary conductors not over 3 m (10 ft.) long, secondary conductors not over 7.5 m (25 ft.) long, outside secondary conductors, industrial installation secondary conductors not over 7.5 m (25 ft.) long, and secondary conductors from a feeder tapped transformer.
(D) Service Conductors
(E) Busway Taps. Busways and their taps can be protected in accordance with Sections 364.10 through 364.14.
(F) Motor Circuit Taps. Motor branch circuit conductors can be protected as indicated in Sections 430.28 and 430.53.
(G) Conductors from Generator Terminals. They can be protected as indicated in Section 445.4 if sized as per 445.5.
| 240.22 | Grounded Conductors |
No overcurrent device should be placed in series with a grounded conductor unless it simultaneously opens all other conductors of the circuit or when required by Sections 430.36 and 430.37.
| 240.23 | Change in Size of Grounded Conductor |
| 240.24 | Location in or on Premises |
Overcurrent devices must be readily accessible. The center of the grip of the handle on the overcurrent device has to be installed so that it is not more than 2.0 m (6 ft. 7 in.) above the floor or working platform at its highest position. There are four exceptions. Each occupant must have access to the ones protecting the conductors for his or her occupancy. The overcurrent devices must not be exposed to physical damage and must not be located near easily ignitible material or in bathrooms of dwelling units or guest rooms or guest suites of hotels and motels. Refer to the NEC® for certain exceptions.
III. Enclosures
| 240.30 | General |
| 240.32 | Damp or Wet Locations |
| 240.33 | Vertical Position |
IV. Disconnecting and Guarding
| 240.40 | Disconnecting Means for Fuses |
In general, the disconnection means must be provided on the supply side of the fuse. This does not hold true for service current-limiting devices as per Section 230.82 or single disconnecting devices for multiple sets of fuses as per Section 430.112 and Section 424.22(C).
| 240.41 | Arcing or Suddenly Moving Parts |
V. Plug Fuses, Fuseholders, and Adapters
These are not permitted in circuits where the voltage between conductors is more than 125 V except with a grounded neutral and not more than 150 V to ground. There are other requirements.
| 240.51 | Edison-Base Fuses |
| 240.52 | Edison-Base Fuseholders |
| 240.53 | Type S Fuses |
| 240.54 | Type S Fuses, Adapters, and Fuseholders |
VI. Cartridge Fuses and Fuseholders
These are permitted in circuits operating at 300 V between conductors if rated 300 V and for single-phase line to neutral circuits where this voltage is not larger than 300 V and the circuit is supplied from a three-phase, four-wire, solidly grounded neutral system. The holders must prevent interchangeability where a fuse can be put into a circuit of lower ampere rating or higher voltage rating. All fuses must be marked, indicating the current, voltage, and interrupting rating, if it is current limiting, and the manufacturer's name and trademark. The interrupting rating is not required when they are used for supplementary protection. Class H cartridge fuses that are renewable type can be used for replacement only in existing installations where there has been no overfusing or tampering.
VII. Circuit Breakers
| 240.80 | Method of Operation |
Normally, they must be trip free and capable of manual operation in addition to other normal means, such as electrical or pneumatic operation.
Must indicate on or offon is up position if mounted vertically.
They must all be properly marked. When properly used as a switch, they must be approved for switching duty and marked SWD or HID. There are requirements for voltage marking, interrupting ratings, and location.
| 240.85 | Applications |
| 240.86 | Series Rating |
VIII. Supervised Industrial Locations
| 240.90 | General |
| 240.92 | Location in Circuit |
IX. Overcurrent Protection over 600 Volts, Nominal
| 240.100 | Feeders and Branch Circuits |
| 240.101 | Additional Requirements for Feeders |
Page 4
I. General
Generally gives requirements for grounding and bonding.
| 250.2 | Definitions |
| 250.3 | Application of Other Articles |
The following other articles have special grounding requirements:
| Agricultural Buildings | 547.9 and 547.10 | |
| Audio Signal Processing, Amplification, and Reproduction Equipment | 640.7 | |
| Branch Circuits | 210.5 | |
| 210.6 | ||
| 406.3 | ||
| Cablebus | 370.9 | |
| Cable trays | 392 | 392.3(C), |
| 392.7 | ||
| Capacitors | 460.10 | |
| 460.27 | ||
| Circuits and Equipment Operating at Less Than 50 Volts | 720 | |
| Class 1, Class 2, and Class 3 | 725.6 | |
| Closed-Loop and Programmed Power Distribution | 780.3 | |
| Communications Circuits | 800 | |
| Community Antenna Television and Radio Distribution Systems | 820.33 | |
| 820.40 | ||
| 820.41 | ||
| Conductors for General Wiring | 310 | |
| Cranes and Hoists | 610 | |
| Electrically Driven or Controlled Irrigation Machines | 675.11(C) | |
| 675.12 | ||
| 675.13 | ||
| 675.14 | ||
| 675.15 | ||
| Electric Signs and Outline Lighting | 600 | |
| Electrolytic Cells | 668 | |
| Elevators, Dumbwaiters, Escalators, Moving Walks, Wheel Chair Lifts, and Stairway Chair Lifts | 620 | |
| Fire Alarm Systems | 760.6 | |
| Fixed Electric Heating Equipment for Pipelines and Vessels | 427.29 | |
| 427.48 | ||
| Fixed Outdoor Electric Deicing and Snow-Melting Equipment | 426.27 | |
| Flexible Cords and Cables | 400.22 | |
| 400.23 | ||
| Floating Buildings | 553.8 | |
| 553.10 | ||
| 553.11 | ||
| Grounding-Type Receptacles, Adapters, Cord Connectors, and Attachment Plugs | 406.9 | |
| Hazardous (Classified) Locations | 500517 | |
| Health Care Facilities | 517 | |
| Induction and Dielectric Heating Equipment | 665 | |
| Industrial Machinery | 670 | |
| Information Technology Equipment | 645.15 | |
| Intrinsically Safe Systems | 504.50 | |
| Luminaires (lighting fixtures) and Lighting Equipment | 410.17 | |
| 410.18 | ||
| 410.20 | ||
| 410.21 | ||
| 410.105(B) | ||
| Luminaires (lighting fixtures), Lampholders, Lamps, and Receptacles | 410 | |
| Marinas and Boatyards | 555.15 | |
| Mobile Homes and Mobile Home Parks | 550 | |
| Motion Picture and Television Studios and Similar Locations | 530.20 | |
| 530.66 | ||
| Motors, Motor Circuits, and Controllers | 430 | |
| Outlet, Device, Pull and Junction Boxes, Conduit Bodies, and Fittings | 314.4 | |
| 314.25 | ||
| Over 600 Volts, Nominal, Underground Wiring Methods | 350.50(B) | |
| Panelboards | 408.20 | |
| Pipe Organs | 650 | |
| Radio and Television Equipment | 810 | |
| Receptacles and Cord Connectors | 406.3 | |
| Recreational Vehicles and Recreational Vehicle Parks | 551 | |
| Services | 230 | |
| Solar Photovoltaic Systems | 690.41 | |
| 690.42 | ||
| 690.43 | ||
| 690.45 | ||
| 690.47 | ||
| Swimming Pools, Fountains, and Similar Installations | 680 | |
| Switchboards and Panelboards | 408.3(D) | |
| Switches | 404.12 | |
| Theaters, Audience Areas of Motion Picture and Television Studios, and Similar Locations | 520.81 | |
| Transformers and Transformer Vaults | 450.10 | |
| Use of Identification of Grounded Conductors | 200 | |
| X-Ray Equipment | 660 | 517.78 |
| 250.4 | General Requirements for Grounding and Bonding |
(A) Grounded Systems
(1) Electrical System Grounding. If the system is to be grounded, it has to be connected to earth so that it will limit voltages due to lightning, unintentional contact with higher voltages, and line surges. It must also stabilize line voltages during normal operation.
(2) Grounding of Electrical Equipment. Any non-current-carrying conductive material enclosing electrical conductors or equipment, or part of a piece of equipment must be connected to earth.
(3) Bonding of Electrical Equipment. All non-current carrying conductive material which encloses conductors or equipment must be connected together and to the electrical supply source.
(4) Bonding of Electrically Conductive Materials and Other Equipment. Any electrically conductive material that may become energized has to be bonded together and to the supply system at the source.
(5) Effective Ground Fault Current Path. The fault current path has to carry the maximum fault current, have low impedance and be continuous and permanent in nature.
The earth is not to be considered an effective ground-fault current path.
(B) Ungrounded Systems
(1) Grounding of Electrical Equipment. Non-current carrying conductive materials that enclose conductors or equipment must be connected to earth so that it will limit voltages due to lightning, unintentional contact and will limit the voltage to ground.
(2) Bonding of Electrical Equipment. All materials that enclose conductors or equipment must be connected together and to the supply system grounded equipment so that the fault current path carries maximum fault current, has low impedance and is continuous and permanent in nature. It must be capable of carrying the maximum fault current that can occur.
(3) Bonding of Electrically Conductive Materials and Other Equipment. Any electrically conductive material that can become energized has to be bonded together and to the supply system grounding equipment so that the fault current path carries maximum fault current, has low impedance, and is continuous and permanent in nature. It must be capable of carrying the maximum fault current that can occur.
(4) Path for Fault Current. The fault current path has to carry the maximum fault current path and have low impedance from any place on the system so that the overcurrent devices will operate on a second fault. The earth is not to be considered an effective fault current path.
There are two fine print notes.
| 250.6 | Objectionable Current over Grounding Conductors |
The entire electrical system is to be installed to prevent an objectionable flow of current over the grounding system. There is a discussion of alterations to stop objectionable current, limitations to permissible alterations, isolation of objectionable direct- current ground currents, and the fact that temporary currents are not classified as objectionable currents.
| 250.8 | Connection of Grounding and Bonding Equipment |
| 250.10 | Protection of Ground Clamps and Fittings |
| 250.12 | Clean Surfaces |
II. System Grounding
| 250.20 | Alternating-Current Systems to Be Grounded |
The following alternating-current systems must be grounded. Others may be grounded if desired.
(A) Alternating-current systems of less than 50 V must be grounded if supplied by transformer systems of more than 150 V to ground by ungrounded transformer systems and where the conductors are outdoors and overhead.
(B) Alternating-current circuits between 50 and 1000 V of the following types must be grounded:
- Systems of up to 150 V to ground from an ungrounded conductor
- Systems that are three-phase, four-wire with a neutral circuit conductor
- Three-phase, four-wire delta systems with the midpoint of one phase used as a circuit conductor
(C) Alternating-Current Systems 1 kV and Over
(D) Separately Derived Systems. If the source is separately derived, and covered in (A) or (B), it must be grounded as required by Section 250.30.
(E) Impedance Grounded Neutral Systems
| 250.21 | Alternating Current Systems of 50 Volts to 1000 Volts Not Required to Be Grounded |
There are a number of systems that are permitted to be grounded but are not required to be grounded. They are: electric systems used to supply industrial electric furnaces for melting, etc.; separately derived systems used only to supply rectifiers for adjustable speed industrial drives; other systems in accordance with 250.20(B) and separately derived systems supplied by transformers less than 1000 volts provided that special conditions are met. Where an alternating current system is not grounded as permitted above, ground detectors must be installed.
| 250.22 | Circuits Not to Be Grounded |
Those specified in Article 517, circuits for electric cranes used in areas of Class III over combustible fibers as indicated in Section 503.13, circuits for equipment in electrolytic cell working zones noted in Article 668 and lighting systems secondary circuits as noted in Section 411.5(A).
| 250.24 | Grounding Service-Supplied Alternating-Current Systems |
As required, each service must have a grounding electrode conductor connected to the grounded service conductor. The reader should be familiar with the requirements of this article in the NEC®. There is a discussion of system grounding connections in general and specifically from outdoor transformers, dual-fed services, using the main bonding jumper as wire or busbar, and loadside grounding connections. There is also a discussion of systems where the grounded conductor is brought to the service equipment, ungrounded system grounding connections, as well as the grounding electrode conductor.
| 250.26 | Conductor to Be GroundedAlternating-Current Systems |
One conductor must be grounded in a two-wire, single-phase system. The neutral conductor is grounded in a three-wire, single-phase system and a multiphase system where one phase is used as a three-wire, single-phase system. The common conductor is grounded in a multiphase system with one wire common to all phases. A phase conductor is grounded in a multiphase system where one phase is grounded and the neutral conductor is grounded in a multiphase system where one phase is used as a single phase 3 wire system.
| 250.28 | Main Bonding Jumper and System Bonding Jumper |
| 250.30 | Grounding Separately Derived Alternating-Current Systems |
| 250.32 | Buildings or Structures Supplied by Feeder(s) or Branch Circuit(s) |
Each building or structure must have a grounding electrode connected to the building grounding means. There are methods noted for grounded systems, ungrounded systems, where the disconnecting means is located in a separate building or structure on the same premises, and the size of the grounding electrode conductor. The size of grounding electrode conductor to the grounding electrode is given in 250.66 based on the largest ungrounded supply conductor. The reader should refer to this section in the NEC®.
| 250.34 | Portable and Vehicle-Mounted Generators |
| 250.36 | High-Impedance Grounded Neutral Systems |
III. Grounding Electrode System and Grounding Electrode Conductor
| 250.50 | Grounding Electrode System |
All grounding electrodes delineated in 250.52(A)(1) through (A)(6) have to be bonded together to form the grounding electrode system. If none exists, then at least one of the electrodes in 252(A)(4) through (A)(7) must be used.
| 250.52 | Grounding Electrodes |
(A) Electrodes Permitted for Grounding
(1) Metal Underground Water Pipe. It must be at least in contact with the earth for 3 m (10) or more feet. It must be electrically continuous to the point of connection to the grounding electrode system and bonding conductors. Interior water piping can not be used if it is more than 1.52 m (5 feet) from the point of entrance to the building. There is an exception for industrial and commercial buildings under certain conditions.
(2) Metal Frame of the Building or Structure. The metal frame of the building or structure can be used with any of the following methods:
(a) At least 3.0 m (10 ft.) of a structural member is in direct contact with the earth or it is encased in concrete that is in direct contact with the earth
(b) The structural metal frame is bonded to at least one grounding electrode as in 250.52(A)(1), (3), or (4)
(c) The structural metal frame is bonded to at least one or more grounding electrodes as noted in 250.52(A)(5) or (6) and complies with 250.56 or
(d) Any other approved method of establishing a connection to the earth.
(3) Concrete-Encased Electrode. The electrode must be at least 6 m (20 ft.) of 4 AWG bare copper conductor or 6 m (20 ft.) of steel or zinc galvanized reinforcing bars or rods at least 13 mm (½ in.) in diameter. It must be encased in at least 50 mm (2 in.) of concrete within or near the bottom of the foundation.
(4) Ground Ring
(5) Rod and Pipe Electrodes
(6) Plate Electrodes
(7) Other Local Metal Underground Systems or Structures
(B) Electrodes Not Permitted for Grounding. Metal underground gas piping and aluminum electrodes are not permitted. Refer to 250.104(B) for bonding requirements for gas piping.
| 250.53 | Grounding Electrode System Installation |
(A) Rod, Pipe, and Plate Electrodes
(B) Electrode Spacing
(C) Bonding Jumper
(D) Metal Underground Water Pipe
(E) Supplemental Electrode Bonding Site
(F) Ground Ring
(G) Rod and Pipe Electrodes
(H) Plate Electrode
| 250.54 | Supplementary Grounding Electrodes |
They are permitted to be connected to the equipment grounding conductors specified in Section 250.118. The earth can not be used as an effective ground-fault current path as noted in 250.4(A)(5) and 250.4(B)(4). They are not required to comply with bonding requirements of 250.50 or 250.53(C) or resistance requirements of 250.56.
| 250.56 | Resistance of Rod, Pipe, and Plate Electrodes |
| 250.58 | Common Grounding Electrode |
Where an ac system is grounded, the system and equipment must be grounded to the same electrode or electrodes bonded together.
| 250.60 | Use of Air Terminal |
You cannot use air terminals conductors and driven pipes, rods, or plate electrodes used for grounding air terminals in lieu of grounding electrodes as noted in Section 250.50. You can bond grounding electrodes of different systems.
| 250.62 | Grounding Electrode Conductor Material |
The material is to be solid or stranded copper, aluminum, or copper-clad aluminum. It can be bare, stranded, covered, or insulated. It must be corrosion resistant.
| 250.64 | Grounding Electrode Conductor Installation |
Install grounding electrode conductors as follows:
(A) Aluminum or Copper-Clad Aluminum Conductors. Where in direct contact with masonry or the earth where there are corrosive conditions, insulated or bare aluminum or copper-clad aluminum grounding conductors are not permitted. When used outside, these types of conductors cannot be used within 450 mm (18 in.) of the earth. The installation must be as noted below.
(B) Securing and Protection Against Physical Damage. If it is 4 AWG copper or aluminum or larger, it must be protected if it is subject to physical damage. 6 AWG wires, if fastened to the building and free from physical damage, do not need protection; if not, they must be protected in the same manner as wires smaller than 6 AWG. Wires smaller than 6 AWG must be enclosed in either rigid metal conduit, intermediate metal conduit, rigid nonmetallic conduit, electrical metallic tubing, or cable armor. In all cases above, the wire or enclosure must be fastened to the surface it is running on.
(C) Continuous. The grounding electrode conductors cannot have a splice or joint. A splice will be permitted only as noted below in (1) through (4).
(1) An irreversible compression-type fitting is used which is listed as grounding and bonding equipment or by an exothermic welding process.
(2) Sections of busbars can be connected together to form a grounding electrode conductor.
(3) Bonding jumpers from grounding electrodes and grounding electrode conductors can be connected to either an aluminum or copper busbar when the busbar is not less than 6 mm x 50 mm (¼ in. x 2 in.). Connections must be made by using a listed connector or the exothermic welding process. The busbar must be accessible and securely fastened.
(4) The installation must comply with 250.64(A) when aluminum busbars are used.
(D) Grounding Electrode Conductor Taps. Taps to the grounding electrode conductor are permitted where a service has more than one enclosure as noted in Section 230.40, Exception No. 2. The taps must go inside of the enclosure. The common grounding electrode conductor has to be sized in accordance with Section 250.66 based on the sum of the circular mil area of the largest ungrounded service entrance conductor. When, as permitted in 240.40 Exception No. 2, more than one set of service entrance conductors connect directly to a service drop or lateral, then the common grounding electrode conductor must be sized as per Table 250.66 Note 1. The tap conductors can be sized for the largest conductor. The tap conductor has to be connected to the grounding electrode conductor in such a way as to maintain the grounding electrode conductor without a splice.
| 2 or smaller | 1/0 or smaller | 8 | 6 |
| 1 or 1/0 | 2/0 or 3/0 | 6 | 4 |
| 2/0 or 3/0 | 4/0 or 250 | 4 | 2 |
| Over 3/0 through 350 | Over 250 through 500 | 2 | 1/0 |
| Over 350 through 600 | Over 500 through 900 | 1/0 | 3/0 |
| Over 600 through 1100 | Over 900 through 1750 | 2/0 | 4/0 |
| Over 1100 | Over 1750 | 3/0 | 250 |
| Where multiple sets of service-entrance conductors are used as permitted in Section 230.40, Exception No. 2, the equivalent size of the largest service-entrance conductor shall be determined by the largest sum of the areas of the corresponding conductors of each set. Where there are no service-entrance conductors, the grounding electrode conductor size shall be determined by the equivalent size of the largest service-entrance conductor required for the load to be served. |
[1] This table applies to the derived conductors of separately derived ac systems.
[2] See installation restrictions in Section 250.64(A).
(E) Enclosures for Grounding Electrode Conductors. A complete electrical path must be ensured for metal enclosures of grounding electrode conductors. If a raceway is used as protection for a grounding conductor, compliance is required with the appropriate article concerning the raceway.
(F) To Electrodes. A grounding conductor can be run to any convenient grounding electrode in the grounding electrode system or to one or more grounding electrodes or to aluminum or copper busbar as noted in 250.64(C). It must be sized for the largest grounding electrode required by the electrodes connected to it.
| 250.66 | Size of Alternating-Current Grounding Electrode Conductor |
These minimum sizes are given in Table 250.66. There are three special cases.
| 250.68 | Grounding Electrode Conductor Connection to Grounding Electrodes |
It must be accessible and provide an effective and permanent ground. There are two exeptions.
| 250.70 | Methods of Grounding Conductor Connections to Electrodes |
IV. Enclosure, Raceway, and Service Cable Grounding
| 250.80 | Service Raceways and Enclosures |
These metal enclosures and raceways must be grounded. There is an exception for a metal elbow installed in an underground installation under certain conditions.
| 250.84 | Underground Service Cable or Raceway |
(A) Underground Service Cable. A continuous underground armored or metal sheathed service cable bonded to the grounded underground system does not have to have the sheath or armor grounded at the building or structure. The armor or sheath can be insulated from the interior metal raceway conduit or piping.
(B) Underground Service Raceway Containing Cable. If an underground metal service raceway contains a metal sheathed or armored cable that is bonded to the grounded underground system, then it does not have to be grounded at the building or structure. The sheath or armor can be insulated from the interior metal raceway or piping.
| 250.86 | Other Conductor Enclosures and Raceways |
These metal enclosures and raceways must be grounded except as permitted in Section 250.112(I). Note three exceptions: for open wire, knob and tubing, and nonmetallic-sheathed cable; enclosures used to physically protect cable assemblies; and metal elbows under certain conditions.
V. Bonding
Bonding must be provided to make sure there is proper electrical continuity in the grounding system.
(A) Bonding at Services
All service equipment must be bonded, items are listed. A means must be provided for intersystem bonding.
(B) Method of Bonding at the Service
There are four approved methods:
(1) For the grounded service conductor use a method noted in Section 250.8
(2) Threaded couplings or threaded bosses made up wrench tight
(3) Threadless couplings and connectors for where made tight for metal raceways and metal-clad cables
(4) Other listed devices
| 250.94 | Bonding for Other Systems |
| 250.96 | Bonding Other Enclosures |
All items that will be used as grounding conductors must be bonded. There is a provision for isolated grounding circuits.
| 250.97 | Bonding for over 250 Volts |
| 250.98 | Bonding Loosely Jointed Metal Raceways |
| 250.100 | Bonding in Hazardous (Classified) Locations |
In a hazardous location as defined in Article 500, the electrical continuity of non-current carrying metal parts must be accomplished by using any of the methods described in 250.92(B)(2) through (4). This must be done even if supplementary equipment grounding conductors are used.
| 250.102 | Equipment Bonding Jumpers |
| 250.104 | Bonding of Piping Systems and Exposed Structural Steel |
| 250.106 | Lightning Protection Systems |
These ground terminals have to be bonded to the building ground system.
VI. Equipment Grounding and Equipment Grounding Conductors
| 250.110 | Equipment Fastened in Place or Connected by Permanent Wiring Methods (Fixed) |
Metal parts of fixed equipment that are likely to become energized must be grounded if located in a wet or damp location and not isolated, if they can be touched by people and are 2.5 m (8 ft.) or less vertically and 1.5 m (5 ft.) or less horizontally to ground or a grounded object, if in contact with metal, if in a hazardous location, if metal-clad type of wiring is used under certain conditions, and if the voltage is greater than 150 V to ground. There are three exceptions.
| 250.112 | Fastened in Place or Connected by Permanent Wiring Methods (Fixed)Specific |
All exposed metal parts that do not conduct current of the following kinds of equipment and enclosures must be grounded: switchboard frames and structures except two-wire dc where insulated from ground: pipe organs; motor frames; enclosures for motor controllers; elevators and cranes; all electric equipment in commercial garages, theaters, and motion picture studios except pendant lampholders of 150 V or less: electric signs, outline lighting and associated equipment as noted in Article 600; motion picture equipment; power-limited remote-control, signaling, and fire-alarm signaling equipment supplied by Class 1, 2, and 3 circuits where required; luminaires (lighting fixtures) as per Article 410; skid-mounted equipment, motor-operated water pumps, and metal well casings.
| 250.114 | Equipment Connected by Cord and Plug |
There are areas where exposed metal parts (noncurrent-carrying) must be grounded even though connected by cord and plug. This is true of hazardous locations and circuits over 150 V to ground; two exceptions are motors when guarded and electrically heated appliances with special exemptions and insulation to ground. In a residence the following items are required to have equipment grounding: refrigerators, freezers, and air conditioners; clothes washing and clothes drying equipment, dishwashing machines, kitchen waste disposers, information technology equipment, sump pumps, and electrical aquarium equipment; hand-held motor-operated tools, stationary and fixed motor-operated tools, light industrial motor-operated tools; motor-operated hedge clippers, lawn mowers, snow blowers, wet scrubbers, etc.; and portable handlamps. In other than residences, the list is the same as residences, with the addition of cord- and plug-connected appliances in damp or wet locations and tools used in wet or conductive locations. There is an exception for tools and portable handlamps in wet or conductive locations if supplied through an isolating transformer with a secondary ungrounded and not over 50 V.
| 250.116 | Nonelectric Equipment |
The metal parts of this equipment must be grounded: cranes and hoists; elevator cars of nonelectric type; and electric elevators.
| 250.118 | Types of Equipment Grounding Conductors |
The following may be used for equipment grounding conductors.
- Copper or other corrosion-resistant conductor. It can be solid or stranded, and bare, covered, or insulated.
- Rigid metal conduit.
- Intermediate metal conduit.
- Electrical metallic tubing.
- Listed flexible metal conduit that meets the following requirements: the terminations are listed for grounding; the conductors in the conduit are protected by devices that are rated 20 A or less; and the total length of flexible metal conduit, flexible metallic tubing, and liquidtight flexible metal conduit in the same ground return path is not more than 1.8 m (6 ft.); if flexibility is required an equipment grounding conductor is used.
- Listed liquidtight flexible metal conduit meeting certain requirements.
- Flexible metal tubing under certain conditions.
- Armor of Type AC cable.
- The copper sheath of MI metal sheathed cable.
- Type MC cable under certain conditions.
- Cable trays as noted in Sections 318.3(c) and 318.7.
- Cablebus framework and noted in Section 365.2(A).
- Any other continuous metal raceways and auxiliary gutters that are continuous and listed for grounding.
- Listed surface metal raceways
| 250.119 | Identification of Equipment Grounding Conductors |
The equipment grounding conductor can either be bare, insulated, or covered unless there is a specific required by the code. There are identification requirements for conductors. Special requirements are listed for conductors larger than 6 AWG, multi-conductor cable, and flexible cord.
| 250.120 | Equipment Grounding Conductor Installation |
Where it is a raceway, cable tray, cable armor, cable bus, or cable sheath, or a wire in a raceway it must be installed in accordance with the NEC®. Aluminum and copper-clad aluminum can be used under certain circumstances. If the equipment grounding conductor is smaller than 6 AWG, it has to be protected from physical damage except under certain conditions where it is not subject to physical damage.
| 250.122 | Size of Equipment Grounding Conductors |
These minimum sizes are given in Table 250.122. When circuit conductors are run in parallel, the equipment grounding conductor must be run in parallel and sized according to the over-current device rating shown in the table. The conductor never has to be larger than the overcurrent device protecting the circuit conductor to the equipment. There are other requirements and exceptions, including where conductors are adjusted in size to compensate for voltage drop.
| 15 | 14 | 12 |
| 20 | 12 | 10 |
| 30 | 10 | 8 |
| 40 | 10 | 8 |
| 60 | 10 | 8 |
| 100 | 8 | 6 |
| 200 | 6 | 4 |
| 300 | 4 | 2 |
| 400 | 3 | 1 |
| 500 | 2 | 1/0 |
| 600 | 1 | 2/0 |
| 800 | 1/0 | 3/0 |
| 1000 | 2/0 | 4/0 |
| 1200 | 3/0 | 250 |
| 1600 | 4/0 | 350 |
| 2000 | 250 | 400 |
| 2500 | 350 | 600 |
| 3000 | 400 | 600 |
| 4000 | 500 | 800 |
| 5000 | 700 | 1200 |
| 6000 | 800 | 1200 |
| Note: Where necessary comply with 250.4(A)(5) or 250.4(B)(4), the equipment grounding conductor shall be sized larger than this table. |
[1] See installation restrictions in Section 250.120.
| 250.124 | Equipment Grounding Conductor Continuity |
| 250.126 | Identification of Wiring Device Terminals |
VII. Methods of Equipment Grounding
| 250.130 | Equipment Grounding Conductor Connections |
| 250.132 | Short Sections of Raceway |
| 250.134 | Equipment Fastened in Place or Connected by Permanent Wiring Methods (Fixed)Grounding |
| 250.136 | Equipment Considered Effectively Grounded |
(A) This is true when it is electrically connected to a supporting metal rack or structure that is properly grounded. The building's structural steel is not considered an effective grounding method.
(B) Metal car frames
| 250.138 | Cord- and Plug-Connected Equipment |
| 250.140 | Frames for Ranges and Clothes Dryers |
| 250.142 | Use of Grounded Circuit Conductor for Grounding Equipment |
(A) Generally, a grounded circuit conductor can be used to ground equipment on the supply side of the service disconnect, supply side of main disconnects for a separate building [Section 250.32(B)], and in a separate, derived system the supply side of the disconnecting or overcurrent devices.
(B) Generally, a grounded circuit conductor cannot be used to ground equipment on the load side of the service disconnect. There are four exceptions to this:
- As indicated in Section 250.140 for ranges, wall-mounted ovens, etc.
- Grounding meter enclosures if no service ground-fault protection is used, the meter is immediately adjacent to the service disconnecting means, and the grounded circuit conductor is not smaller than noted in Table 250.122 for equipment grounding conductors.
- Dc systems in accordance with Section 250.22, Exception.
- Ground electrode-type boilers over 600 V in accordance with 490.72(E)(1) and 490.74.
| 250.144 | Multiple Circuit Connections |
| 250.146 | Connecting Receptacle Grounding Terminal to Box |
Generally, an equipment bonding jumper must be used unless grounded as follows:
A. Surface Mounted Box. If the box is surface mounted and the yoke makes good electrical contact with the box or a contact yoke or device complying with 250.146(B). There are restrictions on cover-mounted receptacles.
B. Contact Devices or Yokes. Where the receptacle is listed as such with special yokes and screws.
C. Floor Boxes. Floor boxes so listed.
D. Isolated Receptacles. Where there is a requirement for the reduction of electrical noise, an insulated grounding conductor can be used. It is run with the circuit conductors. It can pass through panelboards without connection to the grounding terminal. The grounding terminal in the receptacle can be insulated from the mounting.
| 250.148 | Continuity and Attachment of Equipment Grounding Conductors to Boxes |
VIII. Direct Current Systems
| 250.162 | Direct-Current Systems and Systems to Be Grounded |
| 250.164 | Point of Connection for Direct-Current Systems |
| 250.166 | Size of Direct-Current Grounding Electrode Conductor |
It cannot be smaller than the neutral conductor for a three-wire balancer set or balancer winding. It cannot be smaller than the largest conductor if other than as stated in the preceding sentence. It can never be smaller than 8 AWG copper or 6 AWG aluminum. There are requirements for connections to make electrodes, concrete-encased electrodes, and ground rings.
| 250.168 | Direct-Current Bonding Jumper |
| 250.169 | Underground Direct-Current Separately Derived Systems |
IX. Instruments, Meters, and Relays
| 250.170 | Instrument Transformer Circuits |
| 250.172 | Instrument Transformer Cases |
| 250.174 | Cases of Instruments, Meters, and Relays Operating at Less Than 1000 Volts |
| 250.176 | Cases of Instruments, Meters and Relays Operating at 1 kV and Over |
| 250.178 | Instrument Grounding Conductor |
X. Grounding of Systems and Circuits of 1 kV and over (High Voltage)
If these systems are grounded, they must follow all previous sections as well as this section.
| 250.182 | Derived Neutral Systems |
| 250.184 | Solidly Grounded Neutral Systems |
| 250.186 | Impedance Grounded Neutral Systems |
| 250.188 | Grounding of Systems Supplying Portable or Mobile Equipment |
| 250.190 | Grounding of Equipment |
Page 5
I. General
| 280.1 | Scope |
| 280.2 | Definition |
| 280.3 | Number Required |
| 280.4 | Surge-Arrester Selection |
II. Installation
| 280.11 | Location |
| 280.12 | Routing of Surge-Arrester Connections |
III. Connecting Surge Arresters
| 280.21 | Installed at Services of Less Than 1000 Volts |
| 280.22 | Installed on the Load Side of Services of Less Than 1000 Volts |
| 280.23 | Circuits of 1 kV and overSurge-Arrester Conductors |
| 280.24 | Circuits of 1 kV and overInterconnections |
| 280.25 | Grounding |
Article 90 Introduction
General
Wiring and Protection
Wiring Methods and Materials
Equipment for General Use
Special Occupancies
Special Equipment
- Article 645 Information Technology Equipment
Special Conditions
Tables
Annex C. Conduit and Tubing Fill Tables for Conductors and Fixture Wires of the Same Size
Annex D. Examples
- Annex D. Examples
- Example No. D1(a) One-Family Dwelling
- Example No. D1(b) One-Family Dwelling
- Example No. D2(a) Optional Calculation for One-Family Dwelling Heating Larger than Air Conditioning [See Section 220.82]
- Example No. D2(b) Optional Calculation for One-Family Dwelling, Air Conditioning Larger than Heating [See 220.82(A) and 220.82(C)]
- Example No. D2(c) Optional Calculation for One-Family Dwelling with Heat Pump(Single-Phase, 240/120-Volt Service) (See 220.82)
- Example No. D3 Store Building
- Example D3(a) Industrial Feeders in a Common Raceway
- Example No. D4(a) Multifamily Dwelling
- Example No. D4(b) Optional Calculation for Multifamily Dwelling
- Example No. D5(a) Multifamily Dwelling Served at 208Y/120 Volts, Three Phase
- Example No. D5(b) Optional Calculation for Multifamily Dwelling Served at 208Y/120 Volts, Three Phase
- Example No. D6 Maximum Demand for Range Loads
- Example No. D8 Motor Circuit Conductors, Overload Protection, and Short-Circuit and Ground-Fault Protection
- Example No. D9 Feeder Ampacity Determination for Generator Field Control
- Example No. D10 Feeder Ampacity Determination for Adjustable-Speed Drive Control [See 215.2, 430.24, 620.13, 620.14, 620.61, Tables 430.22(E), and 620.14]
- Example No. D11 Mobile Home (See 550.18)
- Example No. D12 Park Trailer (See 552.47)
Annex E. Types of Construction
- Annex E. Types of Construction
show all menu
Page 6
I. General
| 285.1 | Scope |
| 285.2 | Definition |
| 285.3 | Uses Not Permitted |
| 285.4 | Number Required |
| 285.5 | Listing |
| 285.6 | Short Circuit Current Rating |
II. Installation
| 285.11 | Location |
| 280.12 | Routing of Connections |
III. Connecting Transient Voltage Surge Suppressors
| 285.21 | Connection |
| 280.25 | Grounding |
Article 90 Introduction
General
Wiring and Protection
Wiring Methods and Materials
Equipment for General Use
Special Occupancies
Special Equipment
- Article 645 Information Technology Equipment
Special Conditions
Tables
Annex C. Conduit and Tubing Fill Tables for Conductors and Fixture Wires of the Same Size
Annex D. Examples
- Annex D. Examples
- Example No. D1(a) One-Family Dwelling
- Example No. D1(b) One-Family Dwelling
- Example No. D2(a) Optional Calculation for One-Family Dwelling Heating Larger than Air Conditioning [See Section 220.82]
- Example No. D2(b) Optional Calculation for One-Family Dwelling, Air Conditioning Larger than Heating [See 220.82(A) and 220.82(C)]
- Example No. D2(c) Optional Calculation for One-Family Dwelling with Heat Pump(Single-Phase, 240/120-Volt Service) (See 220.82)
- Example No. D3 Store Building
- Example D3(a) Industrial Feeders in a Common Raceway
- Example No. D4(a) Multifamily Dwelling
- Example No. D4(b) Optional Calculation for Multifamily Dwelling
- Example No. D5(a) Multifamily Dwelling Served at 208Y/120 Volts, Three Phase
- Example No. D5(b) Optional Calculation for Multifamily Dwelling Served at 208Y/120 Volts, Three Phase
- Example No. D6 Maximum Demand for Range Loads
- Example No. D8 Motor Circuit Conductors, Overload Protection, and Short-Circuit and Ground-Fault Protection
- Example No. D9 Feeder Ampacity Determination for Generator Field Control
- Example No. D10 Feeder Ampacity Determination for Adjustable-Speed Drive Control [See 215.2, 430.24, 620.13, 620.14, 620.61, Tables 430.22(E), and 620.14]
- Example No. D11 Mobile Home (See 550.18)
- Example No. D12 Park Trailer (See 552.47)
Annex E. Types of Construction
- Annex E. Types of Construction
show all menu
Page 7
I. General Requirements
This article applies to all wiring installations except as noted in other articles. It does not apply to integral parts of equipment (e.g., motors, motor control centers, etc.) Metric designators and trade sizes for conduit, tubing, etc. are shown in Table 300.1(C).
| 12 | 3/8 |
| 16 | ½ |
| 21 | ¾ |
| 27 | 1 |
| 35 | 1¼ |
| 41 | 1½ |
| 53 | 2 |
| 63 | 2½ |
| 78 | 3 |
| 91 | 3½ |
| 103 | 4 |
| 129 | 5 |
| 155 | 6 |
| Note: The metric designators and trade sizes are for identification purposes only and are not actual dimensions. |
This chapter applies to voltages up to and including 600 V when not otherwise noted and over 600 V only when specifically mentioned in the National Electrical Code®.
(A) Single Conductors. The single conductors that are specified in Table 310.13 can be installed only as part of a recognized wiring method described in Chapter 3. Single overhead conductors are permitted if installed in accordance with 225.6.
(B) Conductors of the Same Circuit. All conductors of the same circuit including the grounded conductor and equipment grounding conductors must be installed in the same raceway, cable, etc. There are exceptions.
(C) Conductors of Different Systems
(1) 600 Volts, Nominal, or Less. Conductors of 600 V or less can occupy the same wiring enclosure if all conductors have insulation rated for the maximum voltage used. Refer to Section 690.4(B) for solar photovoltaic systems and to Section 725.55(A) for Class 2 and Class 3 conductors.
(2) Over 600 Volts, Nominal. Conductors of over 600 V cannot be in the same wiring enclosure with those rated 600 V or less except for secondary wiring to electric discharge lamps, primary leads of electric discharge lamp ballasts, and excitation, control, relay, ammeter conductors, motor switch gear and control assemblies, and in manholes under certain conditions.
Reference should be made to this section in the NEC® for a complete explanation.
| 300.4 | Protection against Physical Damage |
| 300.5 | Underground Installations |
(A) Minimum Cover Requirements. The cover requirements for direct buried cable or conduit are shown in Table 300.5. The reader should refer to it.
(B) Listing
(C) Underground Cables under Buildings
(D) Protection from Damage
(E) Splices and Taps
(F) Backfill
(G) Raceway Seals
(H) Bushing
(I) Conductors of the Same Circuit
(J) Ground Movement
(K) Directional Boring
| 300.6 | Protection against Corrosion |
Generally, all material used must be suitable for use in the installed environment.
(A) Ferrous Metal Equipment. Ferrous material must be protected both inside and out by a coating of corrosion-resistant material. If corrosion protection is required and threading takes place in the field, then the threads must be coated with an identified electrical conductive, corrosion-resistant compound. Stainless steel need not have a protective coating. If protected only by enamel ferrous metal equipment shall not be used outdoors or in wet locations as noted in 300.6(D). Boxes or cabinets with an approved organic coating and marked "Raintight," "Rainproof," or "Outdoor Type" can be used outdoors. If the material is approved for use in concrete, in direct contact with the earth, or subject to severe corrosion or has approved corrosion protection, then it can be used there.
(B) Non-Ferrous Metal Equipment. Non-ferrous material must have supplementary corrosion protection if embedded in or encased in concrete or in direct contact with the earth.
(C) Nonmetallic Equipment. Nonmetallic equipment must be made of material approved for the conditions in which it is installed. If exposed to sunlight then the material must be listed as sunlight resistant or be identified as sunlight resistant. If exposed to chemicals or their vapors, the material must be inherently resistant to the chemicals or identified for the specific chemical reagent.
(D) Indoor Wet Locations. The cable must be installed with at least 6 mm (¼ in.) of air space from the wall or supporting surface when installed exposed. There is an exception.
| 300.7 | Raceways Exposed to Different Temperatures |
| 300.8 | Installations of Conductors with Other Systems |
| 300.10 | Electrical Continuity of Metal Raceways and Enclosures |
There must be electrical continuity between all metal race-ways, cable armor, and metal enclosures. There are two exceptions.
| 300.11 | Securing and Supporting |
| 300.12 | Mechanical ContinuityRaceways and Cables |
| 300.13 | Mechanical and Electrical ContinuityConductors |
Splices or taps are not permitted within a raceway. Exceptions to this are noted in Sections 300.15; 368.8(A); 376.56; 378.56; 384.56; 386.56; 388.56; or 390.6. In a multiwire branch circuit the continuity cannot depend on device connections that can be removed.
| 300.14 | Length of Free Conductors at Outlets, Junctions, and Switch Points |
At least 150 mm (6 in.) of conductors must be left at every outlet, junction, or switch point for splices or connections. When the opening to the point of connection is less than 200 mm (8 in.), the conductors must extend at least 75 mm (3 in.).
| 300.15 | Boxes, Conduit Bodies or FittingsWhere Required |
For concealed knob and tube wiring a box must be installed at each switch point and outlet. Use fittings and connectors only for the purpose that they are listed and designed for. If the wiring method is conduit, tubing, Type AC cable, Type MC cable, Type MI cable, non-metallic sheathed cable or other cables, then a conduit body or box must be installed at each conductor splice point, switch point, outlet point, termination point, pull point and junction point. This requirement for the use of a conduit body or box is in force unless not required by (A) through (M) following.
(A) Wiring Methods With Interior Access. If the outlet method has a removable cover that is accessible after installation.
(B) Equipment. A wiring compartment or junction box that is part of approved equipment is allowed instead of a box.
(C) Protection. If the cables enter or leave conduit or tubing that is used for support or protection against physical damage. There are requirements for the use of fittings.
(D) Type MI Cable. If accessible fittings are used for straight through splices.
(E) Integral Enclosure. A wiring device with an integral enclosure that has brackets that fasten it to wall or ceilings for use with nonmetallic sheathed cable is permitted.
(F) Fitting. A fitting can be used instead of a conduit body or box as long as there are splices or terminations in the fitting. The fitting has to be accessible after the installation.
(G) Direct-Buried Conductors. As permitted in 300.5(E).
(H) Insulated Devices. As permitted in 334.40(B) where the insulated device is supplied by nonmetallic-sheathed cable.
(I) Enclosures. Where a splice, switch terminal, or pull point is in a cabinet or cut out box in an enclosure for a switch or overcurrent device as noted in 312.8 in a motor controller as noted in 430.10(A) or in a motor center.
(J) Luminaires (Fixtures). If the fixture is used as a raceway as permitted in 410.31 and 410.32.
(K) Embedded. Where conductors are embedded as permitted in 424.40, 424.41(D), 426.22(B), 426.24(A), and 427.19(A) they are not required for splices.
(L) Manholes and Handhole Enclosures. If only qualified persons have access in manholes except when connecting to electrical equipment and compliance with Part V of Article 110 for manholes and 314.30 for handhole enclosures.
(M) Closed Loop. If a device is identified and listed for installation without a box and is used with a closed loop power distribution system.
| 300.16 | Raceway or Cable to Open or Concealed Wiring |
| 300.17 | Number and Size of Conductors in Raceway |
In general, the number and size of conductors in a raceway must allow the dissipation of heat, easy installation, and withdrawal.
| 300.18 | Raceway Installations |
Raceways other than exposed raceways or busways that have hinged or removable covers must be installed complete between outlet, junction, or splicing points before the conductors are installed. Three exceptions are: (1) for prewired assemblies, (2) when necessary for the installation of utilization equipment, and (3) short sections used for protection from physical damage. There is a restriction on the use of welding.
| 300.19 | Supporting Conductors in Vertical Raceways |
Conductors must be supported at the top of vertical risers with additional support as noted in Table 300.19(A) of the NEC® when the rise is greater than the values in that table.
| 300.20 | Induced Currents in Metal Enclosures or Metal Raceways |
The effects of induced currents in metal enclosures must be minimized. This is done by grouping all phases, neutral, and grounding conductors in one raceway. If individual conductors are used, a slot can be cut between the holes made in the metallic enclosure through which the individual conductor passes. There are some exceptions.
| 300.21 | Spread of Fire or Products of Combustion |
| 300.22 | Wiring in Ducts, Plenums, and Other Air-Handling Spaces |
(A) Ducts for Dust, Loose Stock, or Vapor Removal. Wiring of any type is prohibited in these types of installations. This includes ventilation of commercial-type cooking equipment.
(B) Ducts or Plenums Used for Environmental Air. The following can be used when the duct or plenum was specifically made for this purpose: Type MI, Type MC cable with the specified sheath, EMT flexible metallic tubing, intermediate metal conduit, or rigid metal conduit. When necessary to connect physically adjustable items, flexible metal conduit can be used, but only in lengths not longer than 1.2 m (4 ft.). Only devices that act on or sense the contained air, such as thermostats, are permitted. If lighting fixtures are installed for maintenance or repair, they must be of the enclosed gasketed type. This paragraph applies primarily to fabricated ducts and plenums.
(C) Other Space Used for Environmental Air. This paragraph applies to spaces other than those in Sections 300.22(A) and (B) for environmental air handling. Habitable rooms or areas of buildings which are not primarily used for air handling are not included. Only totally enclosed nonventilated insulated busways that do not have a provision for plug-in connections and Type MI cable, Type MC cable without an overall nonmetallic covering, as well as Type AC cable or other factory-assembled multiconductor control or power cable made to be installed in these areas can be installed in this space. Other types of cables and conductors can be used but only when installed in EMT, flexible metallic tubing, intermediate metal conduit, rigid and flexible metal conduit, where accessible surface metal raceway or metal wireway with metal covers or solid bottom metal cable tray with solid metal covers. Also permitted is electric equipment with a metal enclosure or a listed nonmetallic enclosure with low smoke- and fire-resistive qualities suitable for the ambient temperature unless prohibited in another place in the Code.
(D) Information Technology Equipment. Refer to Article 645.
| 300.23 | Panels Designed to Allow Access |
II. Requirements for Over 600 Volts, Nominal
| 300.31 | Covers Required |
| 300.32 | Conductors of Different Systems |
See Section 300.3(C)(2).
| 300.34 | Conductor Bending Radius |
| 300.35 | Protection against Induction Heating |
| 300.37 | Aboveground Wiring Methods |
| 300.39 | Braid-Covered Insulated Conductors-Exposed Installation |
| 300.40 | Insulation Shielding |
| 300.42 | Moisture or Mechanical Protection for Metal Sheathed Cables |
| 300.50 | Underground Installations |
Page 8
Article 310 is to be used for general requirements for wiring, but not in areas where it is part of an integral device such as a motor, motor controller, or where covered in another part of the NEC®.
Conductors must be insulated and made of copper, copper-clad aluminum, or aluminum unless otherwise specified in the NEC®.
| 310.3 | Stranded Conductors |
Any conductor installed in a raceway must be stranded if it is 8 AWG or larger. This is not required if it is permitted or required in another part of the NEC®.
| 310.4 | Conductors in Parallel |
Conductors 1/0 AWG or larger and having each phase, polarity, neutral, or grounded circuit conductor can be run in parallel if they are the same length, the same size, and of the same material with the same insulation and terminated the same way. They must be electrically joined at both ends. The cables or raceways must have the same physical characteristics if the conductors are run in separate cables or raceways. The same numbers of conductors have to be used in each raceway or cable. The conductors of one phase, neutral, or ground do not have to have the same physical characteristics as those of another to achieve balance. There are four exceptions to this:
1. Section 620.12(A)(1), Exception.
2. If smaller than 1/0 AWG, used for control power to indicating instruments, relays, and similar devices, and in the same raceway, each individual conductor can carry the entire load and the overcurrent rating is not larger than the ampacity of any single conductor.
3. Sizes smaller than 1/0 AWG are allowed for frequencies of 360 Hz and higher provided that Exception 2 is met.
4. With engineering supervision 2 AWG or larger grounded neutral conductors can be run parallel in existing installations.
| 310.5 | Minimum Size of Conductors |
Minimum sizes are shown in Table 310.5 except as permitted in other sections of the Code®. For voltages up to 2000, it is 14 AWG for copper and 12 AWG for aluminum or copper-clad aluminum.
| 310.6 | Shielding |
| 310.7 | Direct Burial Conductors |
| 310.8 | Locations |
In dry locations any type of insulated conductor or cable noted in the Code can be used. Use only Type RHW, TW, THW, MTW, RHW-2, THW-2, THHW, THHW-2, THWN, THWN-2, XHHW, XHHW-2, ZW, or a type listed as such for a wet location, or a moisture impervious metal-sheathed conductor. For dry and damp locations use Types FEP, FEPB, MTW, PFA, RHW, RHH, RHW-2, SA, XHH, XHHW, XHHW-2, THHN, THW-2, THW, THHW, THHW-2, THWN, THWN-2, TW, Z, or ZW. If conductors are exposed to direct sunlight the cables must be listed as sunlight resistant; or conductors must be listed and identified as sunlight resistant; or insulated conductors can be covered with tape, sleeving, or similar material that is listed for the application and identified as sunlight resistant.
| 310.9 | Corrosive Conditions |
| 310.10 | Temperature Limitations of Conductors |
| 310.11 | Marking |
All conductors and cables must have marked on them the maximum rated voltage, the proper letter type, the manufacturer's name or trademark, the AWG size or circular mil area, and cable assemblies where the neutral conductor is smaller than the ungrounded conductor. The size markings should be on the surface and spaced not more than 610 mm (24 in.) for eight types of cables. Other markings may be spaced 1.0 m (40 in.) apart. Certain cables can use marker tape inside the cable. Refer to this section in the NEC® for specific types where marker tape is permitted, which cables can have the size located elsewhere, and suffix designations for number of conductors. Special characteristics can be surface-marked on conductors listed in Chapter 3.
| 310.12 | Conductor Identification |
(A) Grounded Conductors. Insulated grounded conductors must be identified as noted in Section 200.6.
(B) Equipment Grounding Conductors. Equipment grounding conductors must be as noted in Section 250.119.
(C) Ungrounded Conductors. These must be distinguished from grounded and grounding conductors.
| 310.13 | Conductor Constructions and Applications |
Insulated conductors must be in accordance with Tables 310.13 and 310.61 through 310.64.
| 310.14 | Aluminum Conductor Material |
| 310.15 | Ampacities for Conductors Rated 0-2000 Volts |
(A) General
(1) Tables or Engineering Supervision. Ampacities can be determined by tables as provided in (B) or under engineering supervision as noted in 310.15(C).
(2) Selection of Ampacity. If more than one ampacity is determined from the tables or calculations, the lowest value must be used. There is one exception for adjacent portions of a circuit under certain circumstances.
(B) Tables. Ampacities are noted in the Allowable Ampacities Tables 310.16 through 310.19 and 310.20 through 310.23 for conductors rated 0 to 2000 volts. They can be modified by paragraphs (1) through (6).
| 18 | . . . . | . . . . | 14 | . . . . | . . . . | . . . . | . . . . |
| 16 | . . . . | . . . . | 18 | . . . . | . . . . | . . . . | . . . . |
| 14[*] | 20 | 20 | 25 | . . . . | . . . . | . . . . | . . . . |
| 12[*] | 25 | 25 | 30 | 20 | 20 | 25 | 12[*] |
| 10[*] | 30 | 35 | 40 | 25 | 30 | 35 | 10[*] |
| 8 | 40 | 50 | 55 | 30 | 40 | 45 | 8 |
| 6 | 55 | 65 | 75 | 40 | 50 | 60 | 6 |
| 4 | 70 | 85 | 95 | 55 | 65 | 75 | 4 |
| 3 | 85 | 100 | 110 | 65 | 75 | 85 | 3 |
| 2 | 95 | 115 | 130 | 75 | 90 | 100 | 2 |
| 1 | 110 | 130 | 150 | 85 | 100 | 115 | 1 |
| 1/0 | 125 | 150 | 170 | 100 | 120 | 135 | 1/0 |
| 2/0 | 145 | 175 | 195 | 115 | 135 | 150 | 2/0 |
| 3/0 | 165 | 200 | 225 | 130 | 155 | 175 | 3/0 |
| 4/0 | 195 | 230 | 260 | 150 | 180 | 205 | 4/0 |
| 250 | 215 | 255 | 290 | 170 | 205 | 230 | 250 |
| 300 | 240 | 285 | 320 | 190 | 230 | 255 | 300 |
| 350 | 260 | 310 | 350 | 210 | 250 | 280 | 350 |
| 400 | 280 | 335 | 380 | 225 | 270 | 305 | 400 |
| 500 | 320 | 380 | 430 | 260 | 310 | 350 | 500 |
| 600 | 355 | 420 | 475 | 285 | 340 | 385 | 600 |
| 700 | 385 | 460 | 520 | 310 | 375 | 420 | 700 |
| 750 | 400 | 475 | 535 | 320 | 385 | 435 | 750 |
| 800 | 410 | 490 | 555 | 330 | 395 | 450 | 800 |
| 900 | 435 | 520 | 585 | 355 | 425 | 480 | 900 |
| 1000 | 455 | 545 | 615 | 375 | 445 | 500 | 1000 |
| 1250 | 495 | 590 | 665 | 405 | 485 | 545 | 1250 |
| 1500 | 520 | 625 | 705 | 435 | 520 | 585 | 1500 |
| 1750 | 545 | 650 | 735 | 455 | 545 | 615 | 1750 |
| 2000 | 560 | 665 | 750 | 470 | 560 | 630 | 2000 |
| Correction Factors | |||||||
| Ambient Temp. °C | For ambient temperatures other than 30°C (86°F), multiply the allowable ampacities shown above by the appropriate factor shown below. | Ambient Temp. °F | |||||
| 21-25 | 1.08 | 1.05 | 1.04 | 1.08 | 1.05 | 1.04 | 70-77 |
| 26-30 | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 | 78-86 |
| 31-35 | 0.91 | 0.94 | 0.96 | 0.91 | 0.94 | 0.96 | 87-95 |
| 36-40 | 0.82 | 0.88 | 0.91 | 0.82 | 0.88 | 0.91 | 96-104 |
| 41-45 | 0.71 | 0.82 | 0.87 | 0.71 | 0.82 | 0.87 | 105-113 |
| 46-50 | 0.58 | 0.75 | 0.82 | 0.58 | 0.75 | 0.82 | 114-122 |
| 51-55 | 0.41 | 0.67 | 0.76 | 0.41 | 0.67 | 0.76 | 123-131 |
| 56-60 | . . . . | 0.58 | 0.71 | . . . . | 0.58 | 0.71 | 132-140 |
| 61-70 | . . . . | 0.33 | 0.58 | . . . . | 0.33 | 0.58 | 141-158 |
| 71-80 | . . . . | . . . . | 0.41 | . . . . | . . . . | 0.41 | 159-176 |
| For table headings see page 94. |
[*] See Section 240.4(D).
| 8 | 57 | 66 | 44 | 51 | 8 |
| 6 | 76 | 89 | 59 | 69 | 6 |
| 4 | 101 | 117 | 78 | 91 | 4 |
| 3 | 118 | 138 | 92 | 107 | 3 |
| 2 | 135 | 158 | 106 | 123 | 2 |
| 1 | 158 | 185 | 123 | 144 | 1 |
| 1/0 | 183 | 214 | 143 | 167 | 1/0 |
| 2/0 | 212 | 247 | 165 | 193 | 2/0 |
| 3/0 | 245 | 287 | 192 | 224 | 3/0 |
| 4/0 | 287 | 335 | 224 | 262 | 4/0 |
| 250 | 320 | 374 | 251 | 292 | 250 |
| 300 | 359 | 419 | 282 | 328 | 300 |
| 350 | 397 | 464 | 312 | 364 | 350 |
| 400 | 430 | 503 | 339 | 395 | 400 |
| 500 | 496 | 580 | 392 | 458 | 500 |
| 600 | 553 | 647 | 440 | 514 | 600 |
| 700 | 610 | 714 | 488 | 570 | 700 |
| 750 | 638 | 747 | 512 | 598 | 750 |
| 800 | 660 | 773 | 532 | 622 | 800 |
| 900 | 704 | 826 | 572 | 669 | 900 |
| 1000 | 748 | 879 | 612 | 716 | 1000 |
| CORRECTION FACTORS | |||||
| Ambient Temp. (°C) | For ambient temperatures other than 40° (104°F), multiply the ampacities shown above by the appropriate factor shown below. | Ambient Temp. (°F) | |||
| 2125 | 1.20 | 1.14 | 1.20 | 1.14 | 7077 |
| 2630 | 1.13 | 1.10 | 1.13 | 1.10 | 7986 |
| 3135 | 1.07 | 1.05 | 1.07 | 1.05 | 8895 |
| 3640 | 1.00 | 1.00 | 1.00 | 1.00 | 97104 |
| 4145 | 0.93 | 0.95 | 0.93 | 0.95 | 106113 |
| 4650 | 0.85 | 0.89 | 0.85 | 0.89 | 115122 |
| 5155 | 0.76 | 0.84 | 0.76 | 0.84 | 124131 |
| 5660 | 0.65 | 0.77 | 0.65 | 0.77 | 133140 |
| 6170 | 0.38 | 0.63 | 0.38 | 0.63 | 142158 |
| 7180 | 0.45 | 0.45 | 160176 |
(1) General. For explanation of Type Letters, and for recognized size of conductors for the various conductor insulations, see Section 310.13. For installation requirements, see Sections 310.1 through 310.10, and the various articles of this Code. For flexible cords, see Tables 400.4, 400.5(A), and 400.5(B).
(2) Adjustment Factors
(a) More than Three Current-Carrying Conductors in a Raceway or Cable. Where the number of current-carrying conductors in a raceway or cable exceeds three, or where multi-conductor cables or single conductors are bundled or stacked longer than 600 mm (24 in.) without proper spacing and not in a raceway, the ampacities shall be reduced as shown in the following table Table 310.15(B)(2)(a). In a parallel set of conductors each conductor is counted as a current-carrying conductor. The exceptions to this are listed on the bottom of the table.
| 4 through 6 | 80 |
| 7 through 9 | 70 |
| 10 through 20 | 50 |
| 21 through 30 | 45 |
| 31 through 40 | 40 |
| 41 and above | 35 |
FPN Note 1: See Appendix B, Table B.310.11 for adjustment factors for more than three current-carrying conductors in a raceway or cable with load diversity.
FPN Note 2: For correction factors for conductors in sheet metal auxiliary gutters see 366.23(A) and 376.22 for conductors in metal raceways.
Exception No. 1. When conductors of different systems, as provided in Section 300.3, are installed in a common raceway or cable the derating factors shown in Table 310.15(B)(2)(a) shall apply to the number of power and lighting (Articles 210, 215, 220, and 230) conductors only.
Exception No. 2. For conductors installed in cable trays, the provisions of Section 392.11 shall apply.
Exception No. 3. Derating factors shall not apply to conductors in nipples having a length not exceeding 610 mm (24 in.).
Exception No. 4. Derating factors shall not apply to underground conductors entering or leaving an outdoor trench if those conductors have physical protection in the form of rigid metal conduit, intermediate metal conduit or rigid nonmetallic conduit having a length not exceeding 3 mm (10 ft.) and the number of conductors does not exceed 4.
Exception No. 5. Adjustment factors shall not apply to Type AC cable or to Type MC cable without an overall outer jacket under the following conditions:
(a) Each cable has not more than three current carrying conductors.
(b) The conductors are 12 AWG copper.
(c) Not more than 20 current carrying conductors are bundled, stacked, or supported on "bridle rings."
A 60 percent adjustment factor shall be applied where the current carrying conductors in these cables that are stacked or bundled longer than 600 mm (24 in.) without maintaining spacing exceeds 20.
(b) More than One Conduit, Tube, or Raceway. Spacing between conduits, tubing, or raceways shall be maintained.
(3) Bare Conductors or Covered Conductors
Where bare or covered conductors are used with insulated conductors, their allowable ampacities shall be limited to that permitted for the adjacent insulated conductors.
| 8 | 98 | 8 | 103 | 8 | 76 | 8 | 80 |
| 6 | 124 | 6 | 130 | 6 | 96 | 6 | 101 |
| 4 | 155 | 4 | 163 | 4 | 121 | 4 | 127 |
| 2 | 209 | 2 | 219 | 2 | 163 | 2 | 171 |
| 1/0 | 282 | 1/0 | 297 | 1/0 | 220 | 1/0 | 231 |
| 2/0 | 329 | 2/0 | 344 | 2/0 | 255 | 2/0 | 268 |
| 3/0 | 382 | 3/0 | 401 | 3/0 | 297 | 3/0 | 312 |
| 4/0 | 444 | 4/0 | 466 | 4/0 | 346 | 4/0 | 364 |
| 250 | 494 | 250 | 519 | 266.8 | 403 | 266.8 | 423 |
| 300 | 556 | 300 | 584 | 336.4 | 468 | 336.4 | 492 |
| 500 | 773 | 500 | 812 | 397.5 | 522 | 397.5 | 548 |
| 750 | 1000 | 750 | 1050 | 477.0 | 588 | 477.0 | 617 |
| 1000 | 1193 | 1000 | 1253 | 556.5 | 650 | 556.5 | 682 |
| 636.0 | 709 | 636.0 | 744 | ||||
| 795.0 | 819 | 795.0 | 860 | ||||
| 954.0 | 920 | ||||||
| 1033.5 | 968 | 1033.5 | 1017 | ||||
| 1272 | 1103 | 1272 | 1201 | ||||
| 1590 | 1267 | 1590 | 1381 | ||||
| 2000 | 1454 | 2000 | 1527 |
(4) Neutral Conductor
- A neutral conductor that carries only the unbalanced current from other conductors of the same circuit need not be counted when applying the provisions of Section 310.15(B)(2)(a).
- In a three-wire circuit consisting of two-phase wires and the neutral of a four-wire, three-phase wye-connected system, a common conductor carries approximately the same current as the line to neutral load currents of the other conductors and shall be counted when applying the provisions of Section 310.15(B)(2)(a).
- On a four-wire, three-phase wye circuit where the major portion of the load consists of nonlinear loads there are harmonic curents present in the neutral conductor and the neutral shall be considered to be a current-carrying conductor.
(5) Grounding or Bonding Conductor
A grounding or bonding conductor shall not be counted when applying the provisions of Section 310.15(B)(2)(a).
(6) 120/240 Volts, Three-Wire, Single-Phase Dwelling Services and Feeders
For individual dwelling units of one family, two-family, and multifamily dwellings, conductors, as listed in Table 310.15(B)(6), shall be permitted to be utilized as 120/240-V, three-wire, single-phase service-entrance conductors, service lateral conductors, and feeder conductors that serve as the main power feeder to a dwelling unit and are installed in raceway or cable with or without an equipment grounding conductor. For applications of this section, the main power feeder shall be the feeder(s) between the main disconnect and the lighting and appliance branch circuit panelboard(s). The feeder conductors to a dwelling unit shall not be required to be larger than its service-entrance conductors. The grounded conductor shall be permitted to be smaller than the ungrounded conductors, provided that the requirements of Sections 215.2, 220.61, and 230.42 are met.
| 4 | 2 | 100 |
| 3 | 1 | 110 |
| 2 | 1/0 | 125 |
| 1 | 2/0 | 150 |
| 1/0 | 3/0 | 175 |
| 2/0 | 4/0 | 200 |
| 3/0 | 250 | 225 |
| 4/0 | 300 | 250 |
| 250 | 350 | 300 |
| 350 | 500 | 350 |
| 400 | 600 | 400 |
(C) Engineering Supervision.
With engineering supervision the following formula can be used to calculate ampacities:
where
| TC | = conductor temperature in degrees Celsius (°C) |
| TA | = ambient temperature in degrees Celsius (°C) |
| DELTA TD | = dielectric loss temperature rise |
| RDC | = dc resistance of conductor at temperature TC |
| YC | = component ac resistance resulting from skin effect and proximity effect |
| RCA | = effective thermal resistance between conductor and surrounding ambient |
FPN: See Annex B for examples of formula application.
| 310.60 | Conductors Rated 2001 to 35,000 Volts. |
(A) Definitions.
(B) Ampacities of Conductors Rated 2001 to 35,000 Volts.
(C) Tables.
Page 9
I. Installation
| 312.2 | Damp, Wet, or Hazardous (Classified) Locations |
When installed in wet locations, they must be weatherproof. In damp or wet locations, surface boxes must prevent moisture from entering and have at least 6 mm (¼ in.) of air space between it and the wall or support. Raceways or cables entering above uninsulated live parts in enclosures in wet locations must use fittings listed for wet locations. Nonmetallic enclosures can be installed on concrete, tile, or masonry without an airspace. In hazardous locations conformance must be made with the requirements of Articles 500 through 517.
When installed in noncombustible material, they may be set back 6 mm (¼ in.) When installed in combustible material, they must be flush with the surface.
| 312.4 | Repairing Plaster and Drywall or Plasterboard |
If a plaster, drywall, or plasterboard surface is broken or incomplete it must be repaired so that there are no open spaces or gaps larger than 3 mm (¼ in.) at the edge of the cabinet or cutout box that employs a flush-type cover.
| 312.5 | Cabinets, Cutout Boxes, and Meter Socket Enclosures |
The opening must be closed. When metal cabinets, boxes, or enclosures are used with open wiring or knob-and-tube work, the conductors must come in through an insulated bushing. In dry areas, they may enter through flexible tubing. Cables must be secured to the box. There is an exception.
| 312.6 | Deflection of Conductors |
Refer to Tables 312.6(A) through (C) in the NEC® for minimum width of gutters and bending spaces.
| 312.7 | Space in Enclosures |
| 312.8 | Enclosures for Switches or Overcurrent Devices |
| 312.9 | Side or Back Wiring Spaces or Gutters |
II. Construction Specifications
If metal, it must have corrosion protection. Sheet steel cabinets must be at least 1.35 mm (0.053 in.) thick uncoated. Nonmetallic cabinets must be approved by the authorities.
Article 90 Introduction
General
Wiring and Protection
Wiring Methods and Materials
Equipment for General Use
Special Occupancies
Special Equipment
- Article 645 Information Technology Equipment
Special Conditions
Tables
Annex C. Conduit and Tubing Fill Tables for Conductors and Fixture Wires of the Same Size
Annex D. Examples
- Annex D. Examples
- Example No. D1(a) One-Family Dwelling
- Example No. D1(b) One-Family Dwelling
- Example No. D2(a) Optional Calculation for One-Family Dwelling Heating Larger than Air Conditioning [See Section 220.82]
- Example No. D2(b) Optional Calculation for One-Family Dwelling, Air Conditioning Larger than Heating [See 220.82(A) and 220.82(C)]
- Example No. D2(c) Optional Calculation for One-Family Dwelling with Heat Pump(Single-Phase, 240/120-Volt Service) (See 220.82)
- Example No. D3 Store Building
- Example D3(a) Industrial Feeders in a Common Raceway
- Example No. D4(a) Multifamily Dwelling
- Example No. D4(b) Optional Calculation for Multifamily Dwelling
- Example No. D5(a) Multifamily Dwelling Served at 208Y/120 Volts, Three Phase
- Example No. D5(b) Optional Calculation for Multifamily Dwelling Served at 208Y/120 Volts, Three Phase
- Example No. D6 Maximum Demand for Range Loads
- Example No. D8 Motor Circuit Conductors, Overload Protection, and Short-Circuit and Ground-Fault Protection
- Example No. D9 Feeder Ampacity Determination for Generator Field Control
- Example No. D10 Feeder Ampacity Determination for Adjustable-Speed Drive Control [See 215.2, 430.24, 620.13, 620.14, 620.61, Tables 430.22(E), and 620.14]
- Example No. D11 Mobile Home (See 550.18)
- Example No. D12 Park Trailer (See 552.47)
Annex E. Types of Construction
- Annex E. Types of Construction
show all menu
Page 10
I. Scope and General
Refer to this section in the NEC® for inclusions and exclusions.
These are not permitted if locknuts or bushings are required on the side of the box.
These are only to be used with nonmetallic sheathed cable or raceways, flexible cords, open wire on insulator installations, or knob-and-tube concealed wiring. They can be used with metal raceway or metal-jacketed cable only if there is a means for integral bonding or internal bonding. There are two exceptions.
These must be grounded.
| 314.5 | Short Radius Conduit Bodies |
Conduit bodies, like capped elbows, which enclose 6 AWG or smaller conductors and are used only to allow the installation of the raceway and its conductors can not have splices, taps, or devices and they must be large enough for free space for the conductors.
II. Installation
| 314.15 | Damp, Wet Locations or Hazardous (Classified) Locations |
Moisture must be prevented from getting into the box. They must be listed for use in wet locations. When installed in a hazardous location, conform to Articles 500 through 517.
| 314.16 | Number of Conductors in Outlet, Device and Junction Boxes, and Conduit Bodies |
The reader is referred to this section for complete information. These items must be large enough to allow free space for all the enclosed conductors. The volume of the box as calculated in this section cannot be smaller than the fill calculation. This does not apply to terminal housings supplied with the motors (refer to Section 430.12). For enclosed conductors 4 AWG or larger, the provisions of Section 314.28 must be complied with.
(A) Box Volume Calculations. The volume is the total of the assembled sections and if used, spaces from plaster rings, domed covers, extension rings, and the like that are made from boxes listed in Table 314.16(A) or have the volume marked.
| 100 x 32 | (4 x 1¼) | round/octagonal | 205 | 12.5 | 8 | 7 | 6 | 5 | 5 | 5 | 2 |
| 100 x 38 | (4 x 1½) | round/octagonal | 254 | 15.5 | 10 | 8 | 7 | 6 | 6 | 5 | 3 |
| 100 x 54 | (4 x 21/8) | round/octagonal | 353 | 21.5 | 14 | 12 | 10 | 9 | 8 | 7 | 4 |
| 100 x 32 | (4 x 1¼) | square | 395 | 18.0 | 12 | 10 | 9 | 8 | 7 | 6 | 3 |
| 100 x 38 | (4 x 1½) | square | 344 | 21.0 | 14 | 12 | 10 | 9 | 8 | 7 | 4 |
| 100 x 54 | (4 x 21/8) | square | 497 | 30.3 | 20 | 17 | 15 | 13 | 12 | 10 | 6 |
| 120 x 32 | (4 | square | 418 | 25.5 | 17 | 14 | 12 | 11 | 10 | 8 | 5 |
| 120 x 38 | (4 | square | 484 | 29.5 | 19 | 16 | 14 | 13 | 11 | 9 | 5 |
| 120 x 54 | (4 | square | 689 | 42.0 | 28 | 24 | 21 | 18 | 16 | 14 | 8 |
| 75 x 50 x 38 | (3 x 2 x 1½) | device | 123 | 7.5 | 5 | 4 | 3 | 3 | 3 | 2 | 1 |
| 75 x 50 x 50 | (3 x 2 x 2) | device | 164 | 10.0 | 6 | 5 | 5 | 4 | 4 | 3 | 2 |
| 75 x 50 x 57 | (3 x 2 x 2¼) | device | 172 | 10.5 | 7 | 6 | 5 | 4 | 4 | 3 | 2 |
| 75 x 50 x 65 | (3 x 2 x 2½) | device | 205 | 12.5 | 8 | 7 | 6 | 5 | 5 | 4 | 2 |
| 75 x 50 x 70 | (3 x 2 x 2¾) | device | 230 | 14.0 | 9 | 8 | 7 | 6 | 5 | 4 | 2 |
| 75 x 50 x 90 | (3 x 2 x 3½) | device | 295 | 18.0 | 12 | 10 | 9 | 8 | 7 | 6 | 3 |
| 100 x 54 x 38 | (4 x 21/8 x 1½) | device | 169 | 10.3 | 6 | 5 | 5 | 4 | 4 | 3 | 2 |
| 100 x 54 x 48 | (4 x 21/8 x 17/8) | device | 213 | 13.0 | 8 | 7 | 6 | 5 | 5 | 4 | 2 |
| 100 x 54 x 54 | (4 x 21/8 x 21/8) | device | 238 | 14.5 | 9 | 8 | 7 | 6 | 5 | 4 | 2 |
| 95 x 50 x 65 | (3¾ x 2 x 2½) | masonrybox/gang | 230 | 14.0 | 9 | 8 | 7 | 6 | 5 | 4 | 2 |
| 95 x 50 x 90 | (3¾ x 2 x 3½) | masonry box/gang | 344 | 21.0 | 14 | 12 | 10 | 9 | 8 | 7 | 2 |
| min. 44.5 depth | FSsingle cover/gang (1¾) | 221 | 13.5 | 9 | 7 | 6 | 6 | 5 | 4 | 2 | |
| min. 60.3 depth | FDsingle cover/gang (23/8) | 295 | 18.0 | 12 | 10 | 9 | 8 | 7 | 6 | 3 | |
| min. 44.5 depth | FSmultiple cover/gang (1¾) | 295 | 18.0 | 12 | 10 | 9 | 8 | 7 | 6 | 3 | |
| min. 60.3 depth | FDmultiple cover/gang (23/8) | 395 | 24.0 | 16 | 13 | 12 | 10 | 9 | 8 | 4 |
[*] Where no volume allowances are required by 314.16(B)(2) through 314.16(B)(5).
(1) Standard Boxes. Given in Table 314.16(A).
(2) Other Boxes. If the box is 100 cubic inches or less [except those in Table 314.16(A)] and nonmetallic boxes must have the capacity marked by the manufacturer. If the box is listed in Table 314.16(A) and has a larger capacity, the manufacturer can mark it.
(B) Box Fill Calculations.
(1) Conductor Fill. Every conductor that originates outside the box and terminates or is spliced in the box and each conductor passing through the box is counted once. A conductor that is looped and unbroken which is not less than twice the minimum length for a free conductor as referred to in 300.14 is counted twice. The fill is computed using Table 314.16(B). If a conductor has no part leaving the box, it is not counted. There is an exception for equipment grounding conductors.
(2) Clamp Fill. If an internal clamp is used there, a single volume allowance in accordance with Table 314.16(B) is made based on the largest conductor in the box.
(3) Support Fittings Fill. If a stud or hickey is there, a single volume allowance in accordance with Table 314.16(B) is made based on the largest conductor in the box.
(4) Device or Equipment Fill. For a strap or yoke containing a device or equipment, a double volume allowance is made in accordance with Table 314.16(B) based on the largest conductor connected to the device or equipment.
(5) Equipment Grounding Fill. If equipment grounding conductors come into the box, a single volume allowance is made in accordance with Table 314.16(B) and is based on the largest equipment grounding conductor present. If additional equipment grounding conductors as noted in 250.146(D), come into the box an additional volume allowance is made based on the largest equipment grounding conductor in this set.
| 18 | 24.6 | 1.50 |
| 16 | 28.7 | 1.75 |
| 14 | 32.8 | 2.00 |
| 12 | 36.9 | 2.25 |
| 10 | 41.0 | 2.50 |
| 8 | 49.2 | 3.00 |
| 6 | 81.9 | 5.00 |
(c) Conduit Bodies. Generally conduit bodies enclosing 6 AWG conductors or smaller must have cross-sectional area not less than twice the area of the largest conduit or tubing attached. The maximum number of conductors is shown in Table 1, Chapter 9. There are additional requirements noted in the Code.
| 314.17 | Conductors Entering Boxes, Conduit Bodies, or Fittings |
All openings must be closed. All conductors coming into a box, conduit body, or fitting must be protected against abrasion. Special requirements are indicated with open wiring or concealed knob-and-tube wiring. If cable or raceway is used, the cable or raceway must be fastened to the box, conduit body, or fitting. Refer to Section 300.15(C) of the NEC® for an exception and to Section 300.4(F) for wire 4 AWG or larger. The reader is referred to this section for complete details.
| 314.19 | Boxes Enclosing Flush Devices |
They must be closed on the back and sides and a support for the device (usually a stud or screw hole) must be in the box. The screw that supports the box cannot be used to attach the device.
| 314.20 | In Wall or Ceiling |
When the box is set in concrete, tile, or other noncombustible material, it can be set back as much as 6 mm (¼ in.) When it is set in combustible material, it has to be flush with the finished surface.
| 314.21 | Repairing Plaster and Drywall or Plasterboard |
| 314.22 | Exposed Surface Extensions |
| 314.23 | Supports |
This section details methods of support. It indicates where they are needed and what can be used.
| 314.24 | Depth of Outlet Boxes |
| 314.25 | Covers and Canopies |
| 314.27 | Outlet Boxes |
They must be designed for the purpose to be used (i.e., floor or lighting fixture). A fixture support must be in a lighting fixture box. Cannot be used as sole support for ceiling paddle fans unless listed for that purpose. There are special cases. The reader is referred to this section in the NEC®.
| 314.28 | Pull and Junction Boxes and Conduit Bodies |
(A) Minimum Size. The following rules apply only when the wire is 4 AWG or larger. In a straight pull, the box must be at least 8 times the metric/designator (trade size) of the largest raceway in length. When angle pulls or U-pulls are used, the distance between the raceway entrances and the opposite wall must be at least 6 times the metric designator (trade size) of the largest raceway in a row. In addition, that distance must be increased by the diameter of each additional raceway in any one row on the same wall of the box. Since each row is calculated individually, the largest distance for a single row is used. Two raceways that enclose the same conductor cannot be closer than 6 times the metric designator (trade size) of the larger raceway. There is an exception where the entry is opposite a removable cover. There is also a provision for boxes or conduit bodies whose dimensions are less than calculated where combination of conductors are used.
(B) Conductors in Pull or Junction Boxes
(C) Covers
(D) Permanent Barriers. If a permanent barrier is in a box, each section is considered a box.
| 314.29 | Boxes and Conduit Bodies to Be Accessible |
| 314.30 | Handhole Enclosures |
They must be designed and installed to withstand any load that might be imposed.
(A) Size. For conductors operating at 600 volts or lower, they must be sized as stated in 314.28(A). For conductors operating above 600 volts they must be sized as stated in 314.71. There is a provision for handholes without bottoms.
(B) Wiring Entries. If underground raceways and cable assemblies enter a handhole they must extend into the enclosure but are not required to be mechanically connected to the enclosure.
(C) Handhole Enclosures Without Bottoms. All enclosed conductors, splices, or terminations must be listed for wet locations if installed in a handhole without a bottom.
(D) Covers. They have to have an identifying mark or logo that tells the function of the handhole. The example given in the Code is "electric." They must weigh over 45 kg (100 lb.) or require the use of tools to open. Any metal cover and any exposed conductive surface has to be bonded in accordance with 250.96(A).
III. Construction Specifications
| 314.40 | Metal Boxes, Conduit Bodies, and Fittings |
| 314.41 | Covers |
| 314.42 | Bushings |
| 314.43 | Nonmetallic Boxes |
| 314.44 | Marking |
IV. Pull and Junction Boxes for Use on Systems Over 600 Volts, Nominal
| 314.70 | General |
| 314.71 | Size of Pull and Junction Boxes |
| 314.72 | Construction and Installation Requirements |
Page 11
I. General
| 320.1 | Scope |
| 320.2 | Definition |
This type of cable is composed of insulated conductors in a flexible metal enclosure. Refer to 320.100.
II. Installation
It can be used exposed or concealed and in cable trays where so identified. It is permitted in dry locations and in plaster finish on brick or other masonry except in damp or wet locations. It can also be used in the voids of masonry block or tile walls when the walls are not exposed or subject to excessive moisture or dampness. There is a fine print note that this is not an all-inclusive list.
| 320.12 | Uses Not Permitted |
It cannot be used if subject to physical damage, in damp or wet locations, embedded in plaster finish on brick or any other masonry in damp or wet locations, in air voids of masonry block or tile when the walls are exposed to excessive dampness or moisture, or where it is exposed to corrosive vapors or fumes.
| 320.15 | Exposed Work |
| 320.17 | Through or Parallel to Framing Members |
| 320.23 | In Accessible Attics |
| 320.24 | Bending Radius |
They must be made so that the cable will not be damaged and the radius of the curve of the inner edge cannot be less than five times the diameter of the cable.
| 320.30 | Securing and Supporting |
| 320.40 | Boxes and Fittings |
| 320.80 | Ampacity |
III. Construction Specifications
The cable consists of insulated conductors enclosed in a flexible metal tape armor with a copper or aluminum bonding strip inside and in contact with the armor.
| 320.104 | Conductors |
| 320.108 | Grounding |
| 320.120 | Marking |
Article 90 Introduction
General
Wiring and Protection
Wiring Methods and Materials
Equipment for General Use
Special Occupancies
Special Equipment
- Article 645 Information Technology Equipment
Special Conditions
Tables
Annex C. Conduit and Tubing Fill Tables for Conductors and Fixture Wires of the Same Size
Annex D. Examples
- Annex D. Examples
- Example No. D1(a) One-Family Dwelling
- Example No. D1(b) One-Family Dwelling
- Example No. D2(a) Optional Calculation for One-Family Dwelling Heating Larger than Air Conditioning [See Section 220.82]
- Example No. D2(b) Optional Calculation for One-Family Dwelling, Air Conditioning Larger than Heating [See 220.82(A) and 220.82(C)]
- Example No. D2(c) Optional Calculation for One-Family Dwelling with Heat Pump(Single-Phase, 240/120-Volt Service) (See 220.82)
- Example No. D3 Store Building
- Example D3(a) Industrial Feeders in a Common Raceway
- Example No. D4(a) Multifamily Dwelling
- Example No. D4(b) Optional Calculation for Multifamily Dwelling
- Example No. D5(a) Multifamily Dwelling Served at 208Y/120 Volts, Three Phase
- Example No. D5(b) Optional Calculation for Multifamily Dwelling Served at 208Y/120 Volts, Three Phase
- Example No. D6 Maximum Demand for Range Loads
- Example No. D8 Motor Circuit Conductors, Overload Protection, and Short-Circuit and Ground-Fault Protection
- Example No. D9 Feeder Ampacity Determination for Generator Field Control
- Example No. D10 Feeder Ampacity Determination for Adjustable-Speed Drive Control [See 215.2, 430.24, 620.13, 620.14, 620.61, Tables 430.22(E), and 620.14]
- Example No. D11 Mobile Home (See 550.18)
- Example No. D12 Park Trailer (See 552.47)
Annex E. Types of Construction
- Annex E. Types of Construction
show all menu
Page 12
I. General
| 322.1 | Scope |
| 322.2 | Definition |
II. Installation
| 322.10 | Uses Permitted |
| 322.12 | Uses not Permitted |
| 322.30 | Securing and Supporting |
| 322.40 | Boxes and Fittings |
| 322.56 | Splices and Taps |
III. Construction
| 322.100 | Construction |
| 322.104 | Conductors |
| 322.112 | Insulation |
| 322.120 | Marking |
Article 90 Introduction
General
Wiring and Protection
Wiring Methods and Materials
Equipment for General Use
Special Occupancies
Special Equipment
- Article 645 Information Technology Equipment
Special Conditions
Tables
Annex C. Conduit and Tubing Fill Tables for Conductors and Fixture Wires of the Same Size
Annex D. Examples
- Annex D. Examples
- Example No. D1(a) One-Family Dwelling
- Example No. D1(b) One-Family Dwelling
- Example No. D2(a) Optional Calculation for One-Family Dwelling Heating Larger than Air Conditioning [See Section 220.82]
- Example No. D2(b) Optional Calculation for One-Family Dwelling, Air Conditioning Larger than Heating [See 220.82(A) and 220.82(C)]
- Example No. D2(c) Optional Calculation for One-Family Dwelling with Heat Pump(Single-Phase, 240/120-Volt Service) (See 220.82)
- Example No. D3 Store Building
- Example D3(a) Industrial Feeders in a Common Raceway
- Example No. D4(a) Multifamily Dwelling
- Example No. D4(b) Optional Calculation for Multifamily Dwelling
- Example No. D5(a) Multifamily Dwelling Served at 208Y/120 Volts, Three Phase
- Example No. D5(b) Optional Calculation for Multifamily Dwelling Served at 208Y/120 Volts, Three Phase
- Example No. D6 Maximum Demand for Range Loads
- Example No. D8 Motor Circuit Conductors, Overload Protection, and Short-Circuit and Ground-Fault Protection
- Example No. D9 Feeder Ampacity Determination for Generator Field Control
- Example No. D10 Feeder Ampacity Determination for Adjustable-Speed Drive Control [See 215.2, 430.24, 620.13, 620.14, 620.61, Tables 430.22(E), and 620.14]
- Example No. D11 Mobile Home (See 550.18)
- Example No. D12 Park Trailer (See 552.47)
Annex E. Types of Construction
- Annex E. Types of Construction
show all menu
Page 13
I. General
The wiring covered in this article is a field-installed system to be used for branch circuits under carpet squares.
The reader is referred to the Code for these definitions.
| 324.6 | Listing Requirements |
II. Installation
It can be used for general-purpose, appliance, and individual branch circuits; on floors that are hard, sound, or smooth made of materials like or similar to concrete, ceramic, composition, and wood; on walls in surface metal raceways; in damp locations; and on heated floors where the temperature is higher than 86°F if approved for those temperatures.
The voltage ratings are up to 150 V to ground and up to 300 V between ungrounded conductors. The current ratings are up to 20 A for general-purpose and appliance branch circuits and up to 30 A for individual branch circuits.
When on a floor, it must be covered with carpet squares. Release-type adhesive only is permitted. If it exceeds 2.3 mm (0.09 in.) above floor level it must be feathered or tapered at the edges to floor level. There are other requirements for corrosion resistance and metal-shield connectors.
| 324.12 | Uses Not Permitted |
It cannot be used outdoors, in wet locations, in classified hazardous locations, where there are corrosive vapors present, or in residential, school, or hospital buildings.
| 324.18 | Crossings |
| 324.30 | Securing and Supporting |
| 324.40 | Boxes and Fittings |
| 324.41 | Floor Coverings |
| 324.42 | Devices |
| 324.56 | Splices and Taps |
| 324.60 | Grounding |
III. Construction
| 324.100 | Construction |
| 324.101 | Corrosion Resistance |
| 324.112 | Insulation |
| 324.180 | Markings |
Article 90 Introduction
General
Wiring and Protection
Wiring Methods and Materials
Equipment for General Use
Special Occupancies
Special Equipment
- Article 645 Information Technology Equipment
Special Conditions
Tables
Annex C. Conduit and Tubing Fill Tables for Conductors and Fixture Wires of the Same Size
Annex D. Examples
- Annex D. Examples
- Example No. D1(a) One-Family Dwelling
- Example No. D1(b) One-Family Dwelling
- Example No. D2(a) Optional Calculation for One-Family Dwelling Heating Larger than Air Conditioning [See Section 220.82]
- Example No. D2(b) Optional Calculation for One-Family Dwelling, Air Conditioning Larger than Heating [See 220.82(A) and 220.82(C)]
- Example No. D2(c) Optional Calculation for One-Family Dwelling with Heat Pump(Single-Phase, 240/120-Volt Service) (See 220.82)
- Example No. D3 Store Building
- Example D3(a) Industrial Feeders in a Common Raceway
- Example No. D4(a) Multifamily Dwelling
- Example No. D4(b) Optional Calculation for Multifamily Dwelling
- Example No. D5(a) Multifamily Dwelling Served at 208Y/120 Volts, Three Phase
- Example No. D5(b) Optional Calculation for Multifamily Dwelling Served at 208Y/120 Volts, Three Phase
- Example No. D6 Maximum Demand for Range Loads
- Example No. D8 Motor Circuit Conductors, Overload Protection, and Short-Circuit and Ground-Fault Protection
- Example No. D9 Feeder Ampacity Determination for Generator Field Control
- Example No. D10 Feeder Ampacity Determination for Adjustable-Speed Drive Control [See 215.2, 430.24, 620.13, 620.14, 620.61, Tables 430.22(E), and 620.14]
- Example No. D11 Mobile Home (See 550.18)
- Example No. D12 Park Trailer (See 552.47)
Annex E. Types of Construction
- Annex E. Types of Construction
show all menu
Page 14
I. General
| 326.1 | Scope |
| 326.2 | Definition |
II. Installation
| 326.10 | Uses Permitted |
| 326.12 | Uses Not Permitted |
| 326.24 | Bending Radius |
| 326.26 | Bends |
| 326.40 | Fittings |
| 326.80 | Ampacity |
III. Construction Specifications
| 326.104 | Conductors |
| 326.112 | Insulation |
| 326.116 | Conduit |
| 326.120 | Marking |
Article 90 Introduction
General
Wiring and Protection
Wiring Methods and Materials
Equipment for General Use
Special Occupancies
Special Equipment
- Article 645 Information Technology Equipment
Special Conditions
Tables
Annex C. Conduit and Tubing Fill Tables for Conductors and Fixture Wires of the Same Size
Annex D. Examples
- Annex D. Examples
- Example No. D1(a) One-Family Dwelling
- Example No. D1(b) One-Family Dwelling
- Example No. D2(a) Optional Calculation for One-Family Dwelling Heating Larger than Air Conditioning [See Section 220.82]
- Example No. D2(b) Optional Calculation for One-Family Dwelling, Air Conditioning Larger than Heating [See 220.82(A) and 220.82(C)]
- Example No. D2(c) Optional Calculation for One-Family Dwelling with Heat Pump(Single-Phase, 240/120-Volt Service) (See 220.82)
- Example No. D3 Store Building
- Example D3(a) Industrial Feeders in a Common Raceway
- Example No. D4(a) Multifamily Dwelling
- Example No. D4(b) Optional Calculation for Multifamily Dwelling
- Example No. D5(a) Multifamily Dwelling Served at 208Y/120 Volts, Three Phase
- Example No. D5(b) Optional Calculation for Multifamily Dwelling Served at 208Y/120 Volts, Three Phase
- Example No. D6 Maximum Demand for Range Loads
- Example No. D8 Motor Circuit Conductors, Overload Protection, and Short-Circuit and Ground-Fault Protection
- Example No. D9 Feeder Ampacity Determination for Generator Field Control
- Example No. D10 Feeder Ampacity Determination for Adjustable-Speed Drive Control [See 215.2, 430.24, 620.13, 620.14, 620.61, Tables 430.22(E), and 620.14]
- Example No. D11 Mobile Home (See 550.18)
- Example No. D12 Park Trailer (See 552.47)
Annex E. Types of Construction
- Annex E. Types of Construction
show all menu
Page 15
I. General
| 328.1 | Scope |
| 328.2 | Definition |
This cable is rated above 2000 V and is a single or multiconductor solid dielectric insulated cable.
II. Installation
It can be used in dry or wet locations, in raceways, directly buried in accordance with 300.50, in messenger supported wiring, and in cable trays in accordance with 392(B)(2).
| 328.12 | Uses Not Permitted |
It cannot be used in cable trays unless specified in 392.3(B)(2); nor can it be exposed to direct sunlight or buried unless as specified in 300.50 and unless it is identified for that purpose.
III. Construction Specifications
| 328.100 | Construction |
| 328.120 | Marking |
Article 90 Introduction
General
Wiring and Protection
Wiring Methods and Materials
Equipment for General Use
Special Occupancies
Special Equipment
- Article 645 Information Technology Equipment
Special Conditions
Tables
Annex C. Conduit and Tubing Fill Tables for Conductors and Fixture Wires of the Same Size
Annex D. Examples
- Annex D. Examples
- Example No. D1(a) One-Family Dwelling
- Example No. D1(b) One-Family Dwelling
- Example No. D2(a) Optional Calculation for One-Family Dwelling Heating Larger than Air Conditioning [See Section 220.82]
- Example No. D2(b) Optional Calculation for One-Family Dwelling, Air Conditioning Larger than Heating [See 220.82(A) and 220.82(C)]
- Example No. D2(c) Optional Calculation for One-Family Dwelling with Heat Pump(Single-Phase, 240/120-Volt Service) (See 220.82)
- Example No. D3 Store Building
- Example D3(a) Industrial Feeders in a Common Raceway
- Example No. D4(a) Multifamily Dwelling
- Example No. D4(b) Optional Calculation for Multifamily Dwelling
- Example No. D5(a) Multifamily Dwelling Served at 208Y/120 Volts, Three Phase
- Example No. D5(b) Optional Calculation for Multifamily Dwelling Served at 208Y/120 Volts, Three Phase
- Example No. D6 Maximum Demand for Range Loads
- Example No. D8 Motor Circuit Conductors, Overload Protection, and Short-Circuit and Ground-Fault Protection
- Example No. D9 Feeder Ampacity Determination for Generator Field Control
- Example No. D10 Feeder Ampacity Determination for Adjustable-Speed Drive Control [See 215.2, 430.24, 620.13, 620.14, 620.61, Tables 430.22(E), and 620.14]
- Example No. D11 Mobile Home (See 550.18)
- Example No. D12 Park Trailer (See 552.47)
Annex E. Types of Construction
- Annex E. Types of Construction
show all menu
Page 16
I. General
| 330.1 | Scope |
| 330.2 | Definition |
Metal-clad cable is Type MC. It is a cable in which the conductors are enclosed in a corrugated metal sheath or interlocking metal tape, insulated, and the entire cable is put together at the factory.
II. Installation
This cable can be used for almost all types of applications, including wet locations, provided that it will not sustain physical damage and is not prohibited in another part of the NEC®. A listing is given in the NEC® for both general uses and specific uses. In wet locations one of the following must be adhered to: moisture will not get through the metal cover, a lead sheath that will not let moisture through is put under the metal cover, or the insulated conductors enclosed by the metal cover are listed for a wet location. Refer to this section in the Code.
Type MC cable must be installed in accordance with the requirements of Articles 300, 490, 725, and Section 770.133. When installed in cable tray, direct buried, as service-entrance cable outside buildings or as aerial cable, you must refer to the appropriate articles in the NEC®.
| 330.12 | Uses Not Permitted |
This cable cannot be used in a location where it is subject to corrosive conditions that are destructive. The NEC® gives as examples direct buried cable in earth or concrete, under fills, chlorides, caustic alkalis, and the like.
| 330.17 | Through or Parallel to Framing Members |
It must comply with 300.4.
| 330.23 | In Accessible Attics |
Must comply with 320.23.
The following are the allowable radii of the curve of the inner edge: for shielded conductors, use the greater of either 12 times the diameter of one conductor or 7 times the overall diameter of the cable; for interlocked armor or corrugated sheath, 7 times the diameter of the sheath; for smooth sheath, use the following:
Cable up to 19 mm (¾ in.) diameter: 10 times diameter
Cable between 19 mm (¾) and 38 mm (1½ in.) diameter: 12 times diameter
Cable larger than 38 mm (1½ in.) diameter: 15 times diameter
| 330.30 | Securing and Supporting |
There are requirements for supported and unsupported cables.
| 330.31 | Single Conductors |
| 330.40 | Boxes and Fittings |
| 330.80 | Ampacity |
Refer to 310.15 or 310.60 for 14 AWG and larger conductors. Use Table 402.5 for 18-16 AWG conductors. There are additional requirements for cable installed in cable tray and cable grouped together supported by messenger cable.
C. Construction Specifications
Copper, aluminum, or copper-clad aluminum must be used, either stranded or solid. The smallest sizes allowed are 18 AWG for copper and 12 AWG for aluminum or copper-clad aluminum.
| 330.108 | Equipment Grounding |
| 330.112 | Insulation |
The sheath must be either smooth, welded, and corrugated or interlocking.
Page 17
I. General
| 332.1 | Scope |
| 332.2 | Definition |
Type MI cable is factory assembled with one or more conductors using a highly compressed refractory mineral insulation. The entire assembly is covered with a gastight and liquidtight continuous copper or alloy steel sheath.
II. Installation
It can be used for services, feeders, and branch circuits; power, control, lighting, and signal circuits; wet, dry, or continuously moist locations; exposed or concealed; indoors and outdoors; embedded in concrete, plaster, fill, and other masonry; hazardous locations; underground when protected; corrosive locations that will not harm the sheath; where exposed to gasoline and oil, in or attached to cable trays and in underground runs when protected against corrosion or physical damage.
| 332.12 | Uses Not Permitted |
Where exposed to corrosive materials that will harm the sheath unless it is properly protected and in underground runs unless it is protected against physical damage.
| 332.17 | Through or Parallel to Framing Members |
| 332.24 | Bending Radius |
| 332.30 | Securing and Supporting |
| 332.31 | Single Conductors |
| 332.40 | Boxes and Fittings |
| 332.80 | Ampacity |
III. Construction Specifications
Solid copper, nickel, or nickel-coated copper.
| 332.108 | Equipment Grouding |
| 332.112 | Insulation |
Highly compressed refractory mineral.
Continuous construction that ensures mechanical protection and a moisture seal.
Article 90 Introduction
General
Wiring and Protection
Wiring Methods and Materials
Equipment for General Use
Special Occupancies
Special Equipment
- Article 645 Information Technology Equipment
Special Conditions
Tables
Annex C. Conduit and Tubing Fill Tables for Conductors and Fixture Wires of the Same Size
Annex D. Examples
- Annex D. Examples
- Example No. D1(a) One-Family Dwelling
- Example No. D1(b) One-Family Dwelling
- Example No. D2(a) Optional Calculation for One-Family Dwelling Heating Larger than Air Conditioning [See Section 220.82]
- Example No. D2(b) Optional Calculation for One-Family Dwelling, Air Conditioning Larger than Heating [See 220.82(A) and 220.82(C)]
- Example No. D2(c) Optional Calculation for One-Family Dwelling with Heat Pump(Single-Phase, 240/120-Volt Service) (See 220.82)
- Example No. D3 Store Building
- Example D3(a) Industrial Feeders in a Common Raceway
- Example No. D4(a) Multifamily Dwelling
- Example No. D4(b) Optional Calculation for Multifamily Dwelling
- Example No. D5(a) Multifamily Dwelling Served at 208Y/120 Volts, Three Phase
- Example No. D5(b) Optional Calculation for Multifamily Dwelling Served at 208Y/120 Volts, Three Phase
- Example No. D6 Maximum Demand for Range Loads
- Example No. D8 Motor Circuit Conductors, Overload Protection, and Short-Circuit and Ground-Fault Protection
- Example No. D9 Feeder Ampacity Determination for Generator Field Control
- Example No. D10 Feeder Ampacity Determination for Adjustable-Speed Drive Control [See 215.2, 430.24, 620.13, 620.14, 620.61, Tables 430.22(E), and 620.14]
- Example No. D11 Mobile Home (See 550.18)
- Example No. D12 Park Trailer (See 552.47)
Annex E. Types of Construction
- Annex E. Types of Construction
show all menu
Page 18
I. General
| 334.1 | Scope |
| 334.2 | Definition |
Nonmetallic-sheathed cable is a cable in which the insulated conductors are enclosed in a nonmetallic material that is moisture-resistant and flame-retardant. The cable is put together at the factory. There are definitions for NM, NMC, and NMS.
II. Installation
These types of cable can be used in one- and two-family dwellings, multifamily dwellings of types III, IV, and V construction except as noted in Section 334.12, and cable trays when they are noted for this use. These cables can also be used in other structures of Types III, IV, and V construction with limitations. Type NM cable can be used both in dry locations exposed and concealed as well as being fished in air voids of block and tile if it is not damp or moist. Type NMC cable can be used exposed or concealed in damp, dry, or corrosive locations, inside and outside of block walls, and in shallow chases protected against nails or screws. Type NMS can be used in the same locations as Type NM. The reader is referred to this section of the NEC® for a complete list of locations where these cables can be used.
| 334.12 | Uses Not Permitted |
Type NM, NMC, and NMS cannot be used in any dwelling not permitted in 334.10(1), (2), and (3); as service entrance cable; exposed in suspended or dropped ceilings in other than one family, two family, and multifamily dwellings; in commercial garages; in motion picture studios; in theatres and the like unless otherwise provided in the NEC®; in hoistways or on elevators or escalators; in storage battery rooms; in hazardous locations unless otherwise provided in the NEC®; and embedded in poured cement, concrete, or aggregate. There are additional limitations for Types NM and NMS cable. The reader is referred to this section of the NEC® for a complete list of locations where types NM, NMC, and NMS are not permitted.
| 334.15 | Exposed Work |
| 334.17 | Through or Parallel to Framing Members |
| 334.23 | In Accessible Attics |
| 334.24 | Bending Radius |
| 334.30 | Securing and Supporting |
The cable must be secured at least every 1.4 m (4½ ft.) and not more than 300 mm (12 in.) from a fitting, box, or cabinet. There are requirements for cable trays, unsupported cable, and wiring devices without a separate outlet box.
| 334.40 | Boxes and Fittings |
| 334.80 | Ampacity |
III. Construction Specifications
| 334.100 | Construction |
| 334.104 | Conductors |
| 334.108 | Equipment Grounding |
| 334.112 | Insulation |
| 334.116 | Sheath |
Page 19
I. General
| 336.1 | Scope |
| 336.2 | Definition |
This cable is factory assembled with a nonmetallic jacket containing two or more insulated conductors with or without bare or covered grounding conductors.
II. Installation
This cable can be used for power, lighting, control, and signal circuits; in cable trays, raceways, or supported by messenger wire; under certain conditions where permitted by Article 725 for Class 1 circuits; for nonpower-limited fire alarm circuits in accordance with Section 760.27; and for industrial establishments with qualified supervision and maintenance. There are additional requirements for support, identification, and equipment grounding in industrial locations. If installed in wet locations the cable must be resistant to moisture and corrosive agents.
| 336.12 | Uses Not Permitted |
Type TC cable cannot be used where exposed to physical damage; installed outside of a cable tray system or raceway unless permitted in 336.10(6); where exposed to direct sunlight unless sunlight resistant; and direct buried unless approved for that purpose.
| 336.24 | Bending Radius |
| 336.80 | Ampacity |
III. Construction Specifications
A metallic sheath cannot be put over or under the nonmetallic sheath. Metallic sheaths can be put over groups of conductors, under the outer jacket or both.
Minimum-size conductors are 18 AWG for copper and 12 AWG for aluminum and copper-clad aluminum. Maximum size is 1000 kcmil. 14 AWG copper and larger and 12 AWG or larger aluminum or copper-clad aluminum are to be of the types shown in Table 310.13 or 310.62.
(A) Fire Alarm Systems. It must be installed as noted in Section 760.27 for fire alarms systems.
(B) Thermocouple Circuits. It must be installed as noted in Article 725, Part III. There are additional requirements.
(C) Class 1 Circuit Conductors. When insulated conductors of sizes 18 AWG or 16 AWG copper are used, they shall be as noted in Section 725.27.
The outer jacket must be a flame-retardant, nonmetallic material.
Article 90 Introduction
General
Wiring and Protection
Wiring Methods and Materials
Equipment for General Use
Special Occupancies
Special Equipment
- Article 645 Information Technology Equipment
Special Conditions
Tables
Annex C. Conduit and Tubing Fill Tables for Conductors and Fixture Wires of the Same Size
Annex D. Examples
- Annex D. Examples
- Example No. D1(a) One-Family Dwelling
- Example No. D1(b) One-Family Dwelling
- Example No. D2(a) Optional Calculation for One-Family Dwelling Heating Larger than Air Conditioning [See Section 220.82]
- Example No. D2(b) Optional Calculation for One-Family Dwelling, Air Conditioning Larger than Heating [See 220.82(A) and 220.82(C)]
- Example No. D2(c) Optional Calculation for One-Family Dwelling with Heat Pump(Single-Phase, 240/120-Volt Service) (See 220.82)
- Example No. D3 Store Building
- Example D3(a) Industrial Feeders in a Common Raceway
- Example No. D4(a) Multifamily Dwelling
- Example No. D4(b) Optional Calculation for Multifamily Dwelling
- Example No. D5(a) Multifamily Dwelling Served at 208Y/120 Volts, Three Phase
- Example No. D5(b) Optional Calculation for Multifamily Dwelling Served at 208Y/120 Volts, Three Phase
- Example No. D6 Maximum Demand for Range Loads
- Example No. D8 Motor Circuit Conductors, Overload Protection, and Short-Circuit and Ground-Fault Protection
- Example No. D9 Feeder Ampacity Determination for Generator Field Control
- Example No. D10 Feeder Ampacity Determination for Adjustable-Speed Drive Control [See 215.2, 430.24, 620.13, 620.14, 620.61, Tables 430.22(E), and 620.14]
- Example No. D11 Mobile Home (See 550.18)
- Example No. D12 Park Trailer (See 552.47)
Annex E. Types of Construction
- Annex E. Types of Construction
show all menu
Page 20
I. General
| 338.1 | Scope |
| 338.2 | Definition |
This cable is either Type SE or USE and is used primarily for services. Type SE has a flame-retardant and moisture-resistant cover. Type USE, which is the one used underground, has a moisture-resistant cover.
II. Installation
(A) Service-Entrance Conductors. When used as service- entrance conductors, you must follow 230.6, 230.7, and Parts II, III, and IV of Article 230. If protected as noted in Section 300.5(D), Type USE can come above ground outside in meter enclosures or terminations when used as a service lateral.
(B) Branch Circuits or Feeders.
(1) Grounded Conductor Insulated. Type SE can be used if all conductors are rubber-covered or thermoplastic type.
(2) Grounded Conductor Not Insulated. Generally, Type SE cable can be used where the insulated conductor is used for circuit wiring in a building and where the uninsulated conductor is used only for equipment grounding. There is an exception.
(3) Temperature Limitations. Do not exceed temperature specified.
(4) Installation Methods for Branch Circuits and Feeders.
Review applicable sections of the NEC®.
III. Construction
| 338.100 | Construction |
| 338.120 | Marking |
Article 90 Introduction
General
Wiring and Protection
Wiring Methods and Materials
Equipment for General Use
Special Occupancies
Special Equipment
- Article 645 Information Technology Equipment
Special Conditions
Tables
Annex C. Conduit and Tubing Fill Tables for Conductors and Fixture Wires of the Same Size
Annex D. Examples
- Annex D. Examples
- Example No. D1(a) One-Family Dwelling
- Example No. D1(b) One-Family Dwelling
- Example No. D2(a) Optional Calculation for One-Family Dwelling Heating Larger than Air Conditioning [See Section 220.82]
- Example No. D2(b) Optional Calculation for One-Family Dwelling, Air Conditioning Larger than Heating [See 220.82(A) and 220.82(C)]
- Example No. D2(c) Optional Calculation for One-Family Dwelling with Heat Pump(Single-Phase, 240/120-Volt Service) (See 220.82)
- Example No. D3 Store Building
- Example D3(a) Industrial Feeders in a Common Raceway
- Example No. D4(a) Multifamily Dwelling
- Example No. D4(b) Optional Calculation for Multifamily Dwelling
- Example No. D5(a) Multifamily Dwelling Served at 208Y/120 Volts, Three Phase
- Example No. D5(b) Optional Calculation for Multifamily Dwelling Served at 208Y/120 Volts, Three Phase
- Example No. D6 Maximum Demand for Range Loads
- Example No. D8 Motor Circuit Conductors, Overload Protection, and Short-Circuit and Ground-Fault Protection
- Example No. D9 Feeder Ampacity Determination for Generator Field Control
- Example No. D10 Feeder Ampacity Determination for Adjustable-Speed Drive Control [See 215.2, 430.24, 620.13, 620.14, 620.61, Tables 430.22(E), and 620.14]
- Example No. D11 Mobile Home (See 550.18)
- Example No. D12 Park Trailer (See 552.47)
Annex E. Types of Construction
- Annex E. Types of Construction
show all menu
Page 21
I. General
| 340.1 | Scope |
| 340.2 | Definition |
A factory assembly with an integral covering of nonmetallic material for direct burial in the earth.
| 340.6 | Listing Requirements |
II. Installation
It can be used for underground work including direct burial. Refer to 300.5 for underground requirements. If used as single conductor cables, all conductors of the feeder grounded conductor or branch circuit, including the grounded conductor and equipment grounding conductor, must conform to 300.3. It can be used for interior wiring in wet, dry, or corrosive areas provided that all other conditions are met. In certain of these cases, as described in Section 690.31, it can be used for solar photovoltaic systems. Single conductor cables can be nonheating leads for heating cable. If supported by cable trays, this cable must be multiconductor. If installed in accordance with Parts II and III of Article 334 it can be used as nonmetallic sheathed cable. In this case it must be multiconductor type.
| 340.12 | Uses Not Permitted |
This type of cable cannot be used for service entrances, in commercial garages, in theaters, in storage battery rooms, in motion picture studios, in hazardous locations, in hoistways, in poured cement except as permitted in 424.43, where exposed to direct rays of sun unless approved for sunlight installation, where subject to physical damage, or as an overhead cable except as messanger supported wiring.
| 340.24 | Bending Radius |
| 340.80 | Ampacity |
Refer to 310.15, 60°C (140°F) conductors.
III. Construction Specifications
This cable is Type UF. Sizes allowed are minimum 14 AWG copper or 12 AWG aluminum or copper-clad aluminum and maximum 4/0 AWG.
| 340.108 | Equipment Grounding |
The cable can have an insulated or bare conductor only for equipment grounding purposes.
Moisture resistant type found in Table 310.13. If installed as a substitute for NM cable, the insulation must be rated at 90°C (194°F).
Flame retardant; moisture, fugus, and corrosion resistant, suitable for direct burial in earth.
Page 22
I. General
| 342.1 | Scope |
| 342.2 | Definition |
This conduit is a circular metal raceway threadable and designed for the protection and routing of conductors and cable. It can be used as an equipment grounding conductor with its couplings and fittings.
| 342.6 | Listing Requirements |
IMC, the factory elbows, couplings, and fittings must be listed.
II. Installation
Intermediate metal conduit can be used in most places and under most conditions. It can be used in the earth or in corrosive locations if it has corrosion protection. It can be used in cinder fill only if 50 mm (2 in.) of noncinder concrete is in direct contact, the conduit is 450 mm (18 in.) or more under the fill, or there is proper corrosion protection. In wet locations all supports, belts, screws, etc. must be protected against corrosion.
With the exception of aluminum fittings and enclosures, dissimilar metals in contact must not be used where possible.
The conduit used cannot be smaller than metric designator 16 (trade size ½) or larger than metric designator 103 (trade size 4). See 300.1(C) for metric designators.
| 342.22 | Number of Conductors |
Refer to Chapter 9, Table 1. Cables can be used if not prohibited by cable articles. Cable cannot exceed fill requirements of Table 1, Chapter 9.
The conduit must not be injured. Refer to Table 2, Chapter 9, for the radius of the curve for field bends.
| 342.26 | BendsNumber in One Run |
The maximum that is permitted is not more than 360° in bends between pull points.
| 342.28 | Reaming and Threading |
All rough edges must be removed when the conduit is cut. When threaded in the field, a tapered cutting die with a taper of 1 in 16 (¾ in. taper per foot) must be used.
| 342.30 | Securing and Supporting |
It must be installed as a complete system and fastened and supported as noted in (A) and (B) below.
(A) Securely Fastened. It must be securely fastened within 900 mm (3 ft.) of all boxes, cabinets, conduits, or other conduit terminations. When structural members interfere with this, then the distance can be increased to 1.5 m (5 ft.). If approved, it does not have to be fastened within 900 mm (3 ft.) of a service head above a roof.
(B) Supports. It has to be supported at intervals no longer than 3 m (10 ft.). Table 344.30(B)(2) indicates the spacing of supports for straight runs of conduit with the proper couplings and there is a prevention of the transmission of stresses. Exposed vertical risers can be supported at intervals of 6 m (20 ft.), if the couplings are threaded, firmly supported at top and bottom, and there is no other intermediate support available. Horizontal runs that are supported by framing members not longer than 3 m (10 ft.) apart with supports within 900 mm (3 ft.) of the terminations are permitted.
| 342.42 | Couplings and Connectors |
Threadless couplings and connectors can be used and should be made tight. Comply with 314.15(A). Running threads cannot be used. Use concrete type in concrete and in wet areas. Do not use threadless couplings and connectors on threaded conduit unless it is listed for that use.
A bushing must be used at the point where the conduit goes into a box, fitting, or other enclosure. This is to protect the wire. An exception is made if protection is provided with the box or fitting.
They are permitted only if made in accordance with Section 300.15.
III. Construction Specifications
The conduit must be marked every 1.5 m (5 ft.) with the letter IMC and as required by 110.24.
This type of conduit has a standard length of 3 m (10 ft.) with one coupling and both ends threaded. Shorter or longer lengths with or without couplings or threads are permitted.
Page 23
I. General
| 344.1 | Scope |
| 344.2 | Definition |
Rigid metal conduit is a raceway that is listed, has a cross section that is circular, has integral or associated couplings, is used with listed fittings to give electrical continuity, and is approved for the installation of electrical conductors.
| 344.6 | Listing Requirements |
This type of conduit, associated fittings, factory elbows and couplings must be listed.
II. Installation
(A) All Atmospheric Conditions and Occupancies. It is permitted in all atmospheric conditions and all occupancies. If the conduit's protection against corrosion is only enamel, it can be used only indoors and in areas that do not have severe corrosive problems. Aluminum enclosures and fittings can be used with steel conduit and vice versa.
(B) Corrosion Environments. If the conduit is protected from corrosion and is suitable, the conduit, elbows, couplings, and fittings can be installed in concrete, in areas where there is a severe corrosive problem, and in direct contact with the earth.
(C) Cinder Fill. It cannot be used in or under cinder fill when there may be permanent moisture unless it is suitable for this type of installation, there are 50 mm (2 in.) or more of noncinder concrete all around it, it is at least 450 mm (18 in.) under the fill, or where it is suitable for the condition and has corrosion protection.
(D) Wet Locations. Everything must be corrosion-resistant (bolts, straps, etc.).
Contact between dissimilar metals must be avoided where possible to eliminate galvanic action. Aluminum fittings are permitted with steel and vice versa where not subject to severe corrosion.
Metric designator 16 (trade size ½) is the minimum size permitted unless used for enclosing motor leads [see Section 430.145(B)]. The maximum size permitted is metric designator 155 (trade size 6). See 300.1(C) for metric designators.
| 344.22 | Number of Conductors in Conduit |
Refer to Chapter 9, Table 1. Cables can be used if not prohibited by cable articles. Cable cannot exceed fill requirements of Table 1, Chapter 9.
The conduit must not be damaged and the internal diameter will not be reduced. Refer to Table 2, Chapter 9, for the radius to the center line of the conduit for field bends.
| 344.26 | BendsNumber in One Run |
The maximum that is permitted is not more than 360° in bends between pull points.
| 344.28 | Reaming and Threading |
All rough edges must be removed when the conduit is cut. When threaded in the field, a tapered cutting die 1 in 16 taper (¾ in. taper per foot) must be used.
| 344.30 | Securing and Supporting |
The conduit must be supported at intervals no longer than 3 m (10 ft.) and fastened not more than 900 mm (3 ft.) from a box, fitting, etc. It must be installed as a complete system in accordance with 300.18. Fastening can be increased to 1.5 m (5 ft.) where structural members do not permit fastening within 900 mm (3 ft.). For supports for straight runs with threaded couplings, refer to Table 344.30(B)(2). No stress is to be transmitted to the terminations. Vertical risers from industrial machinery or fixed equipment can have the distance between supports at 6 m (20 ft.) if the conduit uses threaded couplings and is properly supported at the top and bottom. Where approved, the conduit does not have to be fastened within 900 mm (3 ft.) of a service head for a termination of a mast above the roof. Horizontal runs that are supported by openings through framing members not less than 3 m (10 ft.) and fastened within 900 mm (3 ft.) of termination points are permitted.
| 344.42 | Couplings and Connectors |
Threadless couplings and connectors can be used and made tight. Running threads cannot be used. Use concrete type in masonry or concrete. Comply with 314.15(A) in wet locations. Do not use threadless couplings and connectors on threaded conduit unless it is listed for that use.
A bushing must be used at the point where the conduit goes into a box, fitting, or other enclosure. This is to protect the wire. An exception is made if protection is provided with the box or fitting.
Refer to Article 300.15.
It is permitted as an equipment grounding conductor.
III. Construction Specifications
If the conduit is nonferrous of corrosion-resistant material, it must be marked to indicate it. At every 3 m (10 ft.) the conduit must be marked with identification (refer to Section 110.21).
This type of conduit has a standard in length of 3 m (10 ft.) including one attached coupling. It has to be threaded at each end. Smaller and larger lengths can be used with or without couplings and threads.
Page 24
I. General
| 348.1 | Scope |
| 348.2 | Definition |
This is a circular raceway of helically wound, formed, interlocked metal strip.
| 348.6 | Listing Requirements |
Must be listed.
II. Installation
It can be used in exposed and concealed locations.
| 348.12 | Uses Not Permitted |
It cannot be used in wet locations unless approved for this and the liquid does not get into the conduit, in hoistways unless permitted by Section 620.21(A)(1), in storage battery rooms, in hazardous locations unless allowed by Sections 501.4(B) and 504.20, where materials might deteriorate conductors, underground or in poured concrete or aggregate, and where subject to physical damage.
Minimum size permitted is metric designator 12 (trade size 3/8). The use of metric designator 12 (3/8) is allowed for leads to motors [Section 430.145(b)], not longer than 1.8 m (6 ft.) as part of a listed assembly or taps to lighting fixtures [Section 410.67(C)] or utilization equipment, for manufactured wiring systems [Section 604.6(A)], in hoistways Section 620.21, and as permitted by Section 410.77(C) as part of a listed assembly to connect wired fixture sections. There are five exceptions. The maximum size permitted is metric designator 103 (trade size 4).
| 348.22 | Number of Conductors |
Cannot exceed the percentage fill of Table 1, Chapter 9. Cables can be used if not prohibited by cable articles. Cable cannot exceed the fill requirements of Table 1, Chapter 9.
Bends must not damage the conduit and must not reduce the internal diameter of the conduit. Bends can be made with auxiliary equipment manually. The radius of the curve to the centerline can not be less than that shown in Table 1, Chapter 9. Use the "Other Bends" column.
| 348.26 | BendsNumber in One Run |
The maximum number that is permitted is not more than 360 degrees in bends between pull points. The radius of curve of the inner edge of a field bend must comply with Table 346.10.
| 348.28 | Trimming |
| 348.30 | Securing and Supporting |
Securely fasten within 300 mm (12 in.) of a termination point and supports must be not more than 1.4 m (4½ ft.) apart. There is a provision for supports through framing openings. There are four exceptions.
| 348.42 | Couplings and Connectors |
| 348.56 | Splices and Taps |
They can be made only in accordance with 300.15.
| 348.60 | Grounding and Bonding |
An equipment grounding conductor must be installed when the conduit is used to connect equipment where flexibility is needed. It can be used as an equipment grounding conductor where flexibility is not required in accordance with 250.48(5) or (6). The equipment grounding conductor must be installed in accordance with 250.134(B). Equipment bonding conductors must be installed in accordance with 250.102.
Page 25
I. General
| 350.1 | Scope |
| 350.2 | Definition |
This conduit is similar to flexible metal conduit, but it has a jacket over the metal conduit. The jacket is liquidtight, nonmetallic, and sunlight-resistant.
| 350.6 | Listing Requirements |
II. Installation
This conduit can be installed exposed or concealed, directly buried in earth and if protection from liquids, vapor, or solids is necessary or if flexibility is desired. It can be installed in hazardous areas if approved for that installation. Refer to Sections 501.4(B), 502.4, 503.3, 504.20, and 553.7(B).
| 350.12 | Uses Not Permitted |
It cannot be installed when subject to damage or where temperatures exceed that which is approved for the material.
Minimum metric designator 16 (trade size ½). For exceptions, refer to Section 348.20(A). The maximum size allowed is metric designator 103 (trade size 4). Refer to 300.1(C) for metric designators and trade sizes.
| 350.22 | Number of Conductors or Cables |
(A) Metric Designators 16 through 103 (Trade Sizes ½ through 4). Refer to Table 1, Chapter 9. Cables can be used if not prohibited by cable articles. Cables cannot exceed the fill requirements of Table 1, Chapter 9.
(B) Metric Designator 12 (Trade Size 3/8). Refer to the Fittings Outside Conduit columns in Table 348.22.
Bends must not damage the conduit and must not reduce the internal diameter of the conduit. Bends can be made with auxiliary equipment manually. The radius of the curve to the centerline can not be less than that shown in Table 2, Chapter 9. Use the "Other Bends" column.
| 350.26 | BendsNumber in One Run |
The maximum that is permitted is not more than 360° in bends between pull points.
| 350.30 | Securing and Supporting |
It must be supported and secured not more than 1.4 m (4½ ft.) apart. It must be securely fastened within 300 mm (12 in.) of a conduit termination. Four exceptions are for when the conduit is fished, where flexibility is needed, length not exceeding 900 mm (3 ft.) at terminals, lengths not exceeding 1.8 m (6 ft.) from a fixture terminal connection for tap conductors to a lighting fixture as noted in Section 410.67(C) and within accessible ceilings for lengths not exceeding 1.8 m (6 ft.) from the last point where the raceway is fastened, for connections to luminaires or other equipment. Horizontal runs allowed to be supported by the openings in framing members not more than 1.4 m (4½ ft.) apart and fastened within 300 mm (12 in.) of a termination.
| 350.42 | Couplings and Connectors |
| 350.56 | Splices and Taps |
They can be made only in accordance with Section 300.15.
| 350.60 | Grounding and Bonding |
This type of conduit can be used as a means of grounding under certain conditions. Refer to the NEC®.
III. Construction Specifications
Page 26
I. General
| 352.1 | Scope |
| 352.2 | Definition |
A conduit which is circular in cross section and made from a nonmetallic material.
| 352.6 | Listing Requirements |
The RNC, elbows, and associated fittings must be listed.
II. Installation
Some of the uses permitted and other references in the NEC® are: concealed in walls, floors, ceilings, and cinder fill; exposed when not subject to injury; in corrosive locations where approved for that type of location and in accordance with Section 300.6; in dry and damp locations in accordance with Section 352.12; in wet locations where the entire system is installed to prevent water from getting into the conduit and all bolts, screws, and so forth are corrosion resistant and underground in accordance with Sections 300.5 and 300.50. There is a provision for use as a support in certain specific cases.
| 352.12 | Uses Not Permitted |
This type of conduit must not be used in hazardous locations except where permitted by Sections 503.10(A), 504.20, 514.8 exception 2, 515.8, and the Class 1, Division 2 locations in Section 501.10(B)(3); in areas where there might be physical damage to the conduit; in theaters and similar locations except as noted in Articles 518 and 520; where the temperature rating of the conduit is exceeded by that of the conductor insulation; in areas where the ambient temperature exceeds 50°C (122°F) unless otherwise listed; and for supporting fixtures or other equipment not described in 352.10(H).
The minimum size is metric designator 16 (trade size ½). The maximum size is metric designator 155 (trade size 6).
| 352.22 | Number of Conductors |
Cannot exceed the percentage fill of Table 1, Chapter 9. Cables can be used if not prohibited by cable articles. Cable cannot exceed the fill requirements of Table 1, Chapter 9.
The conduit must not be injured. Refer to Table 2, Chapter 9.
| 352.26 | BendsNumber in One Run |
The maximum that is permitted is not more than 360° in bends between pull points.
Remove rough edges on cuts.
| 352.30 | Securing and Supporting |
Refer to Section 300.18 and Table 352.30(B) for spacing of supports. It must be fastened no farther than 900 mm (3 ft.) from a termination point. If it is listed for other securing spacing, it is permitted to follow but not exceed the listing. There is an exception for supports by openings through framing members of horizontal runs.
| 352.44 | Expansion Fittings |
Expansion fittings have to be provided to compensate for thermal expansion and contraction where the change in length according to Table 352.44(A) or (B) will be 6 mm (¼ in.) or greater between securely mounted conduit terminations.
| 5 | 0.30 | 5 | 0.20 | 105 | 4.26 |
| 10 | 0.61 | 10 | 0.41 | 110 | 4.46 |
| 15 | 0.91 | 15 | 0.61 | 115 | 4.66 |
| 20 | 1.22 | 20 | 0.81 | 120 | 4.87 |
| 25 | 1.52 | 25 | 1.01 | 125 | 5.07 |
| 30 | 1.83 | 30 | 1.22 | 130 | 5.27 |
| 35 | 2.13 | 35 | 1.42 | 135 | 5.48 |
| 40 | 2.43 | 40 | 1.62 | 140 | 5.68 |
| 45 | 2.74 | 45 | 1.83 | 145 | 5.88 |
| 50 | 3.04 | 50 | 2.03 | 150 | 6.08 |
| 55 | 3.35 | 55 | 2.23 | 155 | 6.29 |
| 60 | 3.65 | 60 | 2.43 | 160 | 6.49 |
| 65 | 3.95 | 65 | 2.64 | 165 | 6.69 |
| 70 | 4.26 | 70 | 2.84 | 170 | 6.90 |
| 75 | 4.56 | 75 | 3.04 | 175 | 7.10 |
| 80 | 4.87 | 80 | 3.24 | 180 | 7.30 |
| 85 | 5.17 | 85 | 3.45 | 185 | 7.50 |
| 90 | 5.48 | 90 | 3.65 | 190 | 7.71 |
| 95 | 5.78 | 95 | 3.85 | 195 | 7.91 |
| 100 | 6.08 | 100 | 4.06 | 200 | 8.11 |
| 5 | 0.14 | 5 | 0.09 | 105 | 1.89 |
| 10 | 0.27 | 10 | 0.18 | 110 | 1.98 |
| 15 | 0.41 | 15 | 0.27 | 115 | 2.07 |
| 20 | 0.54 | 20 | 0.36 | 120 | 2.16 |
| 25 | 0.68 | 25 | 0.45 | 125 | 2.25 |
| 30 | 0.81 | 30 | 0.54 | 130 | 2.34 |
| 35 | 0.95 | 35 | 0.63 | 135 | 2.43 |
| 40 | 1.08 | 40 | 0.72 | 140 | 2.52 |
| 45 | 1.22 | 45 | 0.81 | 145 | 2.61 |
| 50 | 1.35 | 50 | 0.90 | 150 | 2.70 |
| 55 | 1.49 | 55 | 0.99 | 155 | 2.79 |
| 60 | 1.62 | 60 | 1.08 | 160 | 2.88 |
| 65 | 1.76 | 65 | 1.17 | 165 | 2.97 |
| 70 | 1.89 | 70 | 1.26 | 170 | 3.06 |
| 75 | 2.03 | 75 | 1.35 | 175 | 3.15 |
| 80 | 2.16 | 80 | 1.44 | 180 | 3.24 |
| 85 | 2.30 | 85 | 1.53 | 185 | 3.33 |
| 90 | 2.43 | 90 | 1.62 | 190 | 3.42 |
| 95 | 2.57 | 95 | 1.71 | 195 | 3.51 |
| 100 | 2.70 | 100 | 1.80 | 200 | 3.60 |
A bushing must be used at the point where the conduit goes into a box or fitting unless protection is provided in the box or fitting.
Use approved methods.
They are permitted only in accordance with Section 300.15.
A separate equipment grounding conductor must be installed where equipment grounding is required. There are two exceptions.
III. Construction Specifications
RNC and fittings must be composed of a nonmetallic material. It must be resistant to moisture and chemical atmospheres. Above ground it must be flame resistant, resistant to impact and crushing, resistant to distortion from heat, and resistant to low temperature and sunlight. Below ground it must be resistant to corrosive agents and moisture, be able to withstand crushing and other abuse. If it is direct buried without encasement in concrete, it must be able to resist the continued loading it will encounter.
It must be marked at least every 3 m (10 ft.) in each length. There are requirements for marking on conduit used above and below ground.