Class II equipment symbol:  Show These appliances are also referred to as having “double insulation” since in class II appliances a supplementary insulation is added to the basic insulation (see Figure F70). No conductive parts of a class II appliance must be connected to a protective conductor:
Fig. F70 – Principale of class II insultation level (IEC 60364-4-41 sub-clause 412) A simple example is that of drawing a cable into a PVC conduit. Methods are also described for distribution switchboards.
To protect consumers and livestock from electric shock, the International Electrotechnical Commission (IEC) published IEC 61140, a basic safety publication intended to be a guideline for technical committees when establishing their own publications. The IEC is an international standards organization which sets international standards for electrotechnology. Electrotechnology is the science of how electricity is used in technology. Electrical appliances fall under this category. Before an electrical appliance can be released for consumer consumption, it must undergo portable appliance testing (PAT). To identify which PAT tests should be applied, IEC 61140 classifies electrical appliances into several protection classes. This article will explore the characteristics of each class. Class I,II,III Symbols. Courtesy of Wikipedia. Class I Class I appliances are usually made of metal, have three cables, have a metal Earth pin, and have a fuse in the plug. However, the only way to confirm whether the appliance is Class I is to look for the Class I symbol on the appliance. Examples of Class I appliances are refrigerators, microwaves, kettles, irons, and toasters. Appliances under Class I have two levels of protection: the basic insulation and the earth connection. Inside the appliance, there are three wires connected to three different pins. The wires are called Live, Neutral, and Earth. Their usual colors are respectively brown, blue, and green/yellow (green in the US, Canada, and Japan). Electricity is carried from a power source to an appliance through a circuit. If a circuit is working properly, the power flows from the source to the appliance and returns to the source. The Live wire brings electric current to the appliance. The Neutral wire brings the current back to the power source. The Earth wire provides a way for the current to flow into the ground in the event of a circuit malfunction. Courtesy of Wikimedia Commons. The Live and Neutral wires are connected to the plastic connector. The connector holds them in place to prevent them from touching the metal case. This isolation is called basic insulation. Should the Live or Neutral wire touch the metal case, there will be a fault in the circuit. If the basic insulation fails, the earth connection will act as the next level of protection. The earth connection uses the Earth wire, which is connected to the metal case. Without the presence of the Earth wire, the current will flow through the end user’s body. As a result, the end user may experience an electric shock. To prevent such an incident, the Earth wire will divert the current into the ground. The fuse should then blow either in the plug or the fuse box, or there should be a power trip. The required PAT tests for Class I appliances are the Earth Continuity and Insulation Resistance tests which will check the basic insulation and earth connection. Class II A Class II appliance usually has a plastic cover. The only way to accurately identify it is to look for the Class II appliance symbol. Examples of Class II appliances are hair dryers, DVD players, televisions, computers, and photocopiers. Class II appliances have two layers of insulation. As in the case of Class I appliances, the plastic connector provides the basic insulation. The added layer of insulation is a plastic casing, which provides backup protection. The double insulation removes a need for an earth connection. The only PAT test required is the insulation resistance test. Sometimes, the Class II classification is confused with the Class 2 designation; however, they are different. The Class 2 label is related to power supply, not safety. It also follows another standard, UL 1310. Class III Class III appliances are identified by the Class III symbol. Examples of Class III appliances are laptops, mobile phones, and low energy light bulbs. Class III appliances use an isolating transformer. The transformer has two separate coil windings called the “Primary Winding”, which is connected to the power source, and the “Secondary Winding”, which is connected to the appliance. Each winding is wrapped around opposite sides of a common closed magnetic circuit called the “Core”. The windings have their own circuits. They are known as the Primary and Secondary circuits. The windings do not touch; hence, their isolation gives the transformer its name. Since the insulation is created by the isolated, non-touching windings, to carry a current, voltage needs to be passed through the windings via induction. Basic transformer circuit. Courtesy of Wikimedia Commons. Class III appliances are not required to have an earth connection. Due to the lack of an earth connection, the current is cut off and cannot continue to flow when there is a circuit glitch. Therefore, the end user will not receive an electric shock. PAT testing is not required unless the charging leads fall under Class II. If the appliances are for medical use, they are not considered to be sufficiently safe for mass consumer usage. They must meet additional requirements.
Appliance classes (also known as protection classes) specify measures to prevent dangerous contact voltages on unenergized parts, such as the metallic casing, of an electronic device. In the electrical appliance manufacturing industry, the following appliance classes are defined in IEC 61140 and used to differentiate between the protective-earth connection requirements of devices. Class 0These appliances have no protective-earth connection and feature only a single level of insulation between live parts and exposed metalwork. If permitted at all, Class 0 items are intended for use in dry areas only. A single fault could cause an electric shock or other dangerous occurrence, without triggering the automatic operation of any fuse or circuit breaker. Sales of such items have been prohibited in much of the world for safety reasons, for example in the UK by Section 8 of The Low Voltage Electrical Equipment (Safety) Regulations 1989 and New Zealand by the Electricity Act. A typical example of a Class 0 appliance is the old style of Christmas fairy lights. However, equipment of this class is common in some 120 V countries, and in much of the 230 V developing world, whether permitted officially or not. These appliances do not have their chassis connected to electrical earth. In many countries the plug of a class 0 equipment is such that it cannot be inserted to grounded outlet like Schuko. The failure of such an equipment in a location where there are grounded equipment can cause fatal shock if one touches both. Any Class 1 equipment will act like a Class 0 equipment when connected to an ungrounded outlet. Class IAppliance class I is not only based on the basic insulation, but the casing and other conductive parts are also connected with a low-resistant earth conductor. Hence, these appliances must have their chassis connected to electrical earth (US: ground) by a separate earth conductor (coloured green/yellow in most countries, green in India, USA, Canada and Japan). The earth connection is achieved with a three-conductor mains cable, typically ending with three-prong AC connector which plugs into a corresponding AC outlet. Plugs are designed such that the connection to the protective earth conductor should be the first connection when plugged in. It should also be the last to be broken when the plug is removed.[1] A fault in the appliance which causes a live conductor to contact the casing will cause a current to flow in the earth conductor. If large enough, this current will trip an over-current device (fuse or circuit breaker [CB]) and disconnect the supply. The disconnection time has to be fast enough not to allow fibrillation to start if a person is in contact with the casing at the time. This time and the current rating in turn sets a maximum earth resistance permissible. To provide supplementary protection against high-impedance faults it is common to recommend a residual-current device (RCD) also known as a residual current circuit breaker (RCCB), ground fault circuit interrupter (GFCI), or residual current operated circuit-breaker with integral over-current protection (RCBO), which will cut off the supply of electricity to the appliance if the currents in the two poles of the supply are not equal and opposite. Class 0IElectrical installations where the chassis is connected to earth with a separate terminal, instead of via the mains cable. In effect this provides the same automatic disconnection as Class I, for equipment that otherwise would be Class 0 Class IIA Class II or double insulated electrical appliance uses reinforced protective insulation in addition to basic insulation. Hence, it has been designed in such a way that it does not require a safety connection to electrical earth (ground). The basic requirement is that no single failure can result in dangerous voltage becoming exposed so that it might cause an electric shock and that this is achieved without relying on an earthed metal casing. This is usually achieved at least in part by having at least two layers of insulating material between live parts and the user, or by using reinforced insulation. In Europe, a double insulated appliance must be labelled Class II or double insulated or bear the double insulation symbol: ⧈ (a square inside another square). As such, the appliance should not be connected to an earth conductor because the high-impedance casing will cause only low-fault currents that are unable to trigger the fusible cut-out.[1] Insulated AC/DC power supplies (such as cell-phone chargers) are typically designated as Class II, meaning that the DC output wires are isolated from the AC input. The designation "Class II" should not be confused with the designation "Class 2", as the latter is unrelated to insulation (it originates from standard UL 1310, setting limits on maximum output voltage/current/power). Class IIFE[1] These devices have a Functional Earth "FE". This differs from a protective earth ground in that it does not offer shock protection from a hazardous voltage. However, it does help to mitigate electromagnetic noise or EMI. This is often important in Audio and Medical design. Note as they also include double insulation it means that users will not be able to come into contact with any live parts. Class IIIA Class III appliance is designed to be supplied from a separated extra-low voltage (SELV) power source. The voltage from a SELV supply is low enough that under normal conditions a person can safely come into contact with it without risk of electrical shock. The extra safety features built into Class I and Class II appliances are therefore not required. Specifically, class III appliances are designed without an earth conductor and should not be connected to the earth grounding of the SELV power source.[1] For medical devices, compliance with Class III is not considered sufficient protection, and furthermore, stringent regulations apply to such equipment. Class III appliances are safe to use under "normal" conditions. All electrical equipment should be treated with care and consideration; even with low voltage or power, abusive or unintended actions (e.g. disassembly, overheating, or an incorrect power supply[2]) may still produce dangerous faults. Whilst Class III equipment is considered safe to use without the risk of an electrical shock it does not mean that it will not develop a fault which could be a fire risk. If we take a computer laptop as an example which is powered by a Separated Extra Low Voltage power source. The power source is actually charging the battery of the laptop enabling the laptop to be functional whilst it is being used. The weak link here is the battery itself. Should the battery become faulty and overheat then there is a possible fire risk. Phone chargers are another example, technically the charger is normally a Class II product but the phone itself could be considered a Class III product since the battery is being charged from a SELV source. There are many other products which have to be powered by a SELV source which are charging batteries whilst they are being used and it is the battery that could be prone to overheating. Note the fact that Class III equipment is not considered sufficient protection for medical devices of which could include a number of other random devices.[3] See also
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