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
The International Electrotechnical Commission (IEC; in French: ''Commission électrotechnique internationale'') is an international standards organization that prepares and publishes international standards for all electrical, electronic and r ...
61140 and used to differentiate between the
protective-earth connection requirements of devices.
Class 0
These 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
Electrical injury is a physiological reaction caused by electric current passing through the body. The injury depends on the density of the current, tissue resistance and duration of contact. Very small currents may be imperceptible or produce ...
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 1989and New Zealand by th
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 120V countries, and in much of the 230V 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
"Schuko" () is a registered trademark referring to a system of AC power plugs and sockets that is defined as " CEE 7/3" (sockets) and "CEE 7/4" (plugs). A Schuko plug features two round pins of 4.8 mm diameter (19 mm long, centers 19&n ...
. 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 I
![Schutzklasse 1](https://upload.wikimedia.org/wikipedia/commons/9/9e/Schutzklasse_1.svg)
Appliance 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
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
conductor (
coloured
Coloureds ( af, Kleurlinge or , ) refers to members of multiracial ethnic communities in Southern Africa who may have ancestry from more than one of the various populations inhabiting the region, including African, European, and Asian. South ...
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.
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
Fuse or FUSE may refer to:
Devices
* Fuse (electrical), a device used in electrical systems to protect against excessive current
** Fuse (automotive), a class of fuses for vehicles
* Fuse (hydraulic), a device used in hydraulic systems to protect ...
or
circuit breaker
A circuit breaker is an electrical safety device designed to protect an electrical circuit from damage caused by an overcurrent or short circuit. Its basic function is to interrupt current flow to protect equipment and to prevent the risk ...
B and disconnect the supply. The disconnection time has to be fast enough not to allow
fibrillation
Fibrillation is the rapid, irregular, and unsynchronized contraction of muscle fibers. An important occurrence is with regard to the heart.
Cardiology
There are two major classes of cardiac fibrillation: atrial fibrillation and ventricular fib ...
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
A residual-current device (RCD), residual-current circuit breaker (RCCB) or ground fault circuit interrupter (GFCI) is an electrical safety device that quickly breaks an electrical circuit with leakage current to ground. It is to protect equi ...
(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 0I
Electrical 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 II
![Double insulation symbol](https://upload.wikimedia.org/wikipedia/commons/f/f7/Double_insulation_symbol.svg)
A Class II or double insulated
electrical appliance
A home appliance, also referred to as a domestic appliance, an electric appliance or a household appliance, is a machine which assists in household functions such as cooking, cleaning and food preservation.
Appliances are divided into three ty ...
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
Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to m ...
becoming exposed so that it might cause an
electric shock
Electrical injury is a physiological reaction caused by electric current passing through the body. The injury depends on the density of the current, tissue resistance and duration of contact. Very small currents may be imperceptible or produce ...
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
Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
, 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.
[
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
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 III
A Class III appliance is designed to be supplied from a separated extra-low voltage (SELV
Extra-low voltage (ELV) is an electricity supply voltage and is a part of the Low voltage bandIEC 61140:2016 Chapter 4.2 in a range which carries a low risk of dangerous electrical shock. There are various standards that define extra-low voltage ...
) 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.[ 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) 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 considered sufficient protection for medical devices of which could include a number of other random devices.]
See also
* Double switching frame, A single-switched relay can close inadvertently in response to a single false feed current.
frame, A double-switched relay cannot close inadvertently with the application of the same current. At least two separate faults would be required t ...
* IP Code
The IP code or ingress protection code indicates how well a device is protected against water and dust. It defined by the International Electrotechnical Commission (IEC) under the international standard IEC 60529 which classifies and pro ...
* Mains power plug
AC power plugs and sockets connect electric equipment to the alternating current (AC) mains electricity power supply in buildings and at other sites. Electrical plugs and sockets differ from one another in voltage and electric current, current ...
* Portable appliance testing
In electrical safety testing, portable appliance testing (PAT, PAT inspection or redundantly as PAT testing) is a process in the United Kingdom, the Republic of Ireland, New Zealand and Australia by which electrical appliances are routinely chec ...
References
{{Reflist
Sources
* IEC 61140: Protection against electric shock — Common aspects for installation and equipment. International Electrotechnical Commission. 2001. (formerly: IEC 536-2: Classification of electrical and electronic equipment with regard to protection against electric shock, 1992)
* BS 2754 : 1976 (1999): Memorandum. Construction of electrical equipment for protection against electric shock.
Electric power
IEC standards