Difference between revisions of "Appliance Classes"
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| − | In the electrical appliance manufacturing industry, the following ''' | + | In the electrical appliance manufacturing industry, the following '''IEC protection classes''' are used to differentiate between the protective [[earth]] connection requirements of appliances. |
==Class 0== | ==Class 0== | ||
| − | These appliances have no protective | + | These appliances have no protective earth connection and feature only a single level of insulation and were intended for use in dry areas. A single fault could cause an [[electric shock]] or other dangerous occurrence. Sales of these items have been banned in the UK since 1975. |
==Class I== | ==Class I== | ||
[[Image:Color wire green yellow.svg|thumb|125px|left|green/yellow ground]] | [[Image:Color wire green yellow.svg|thumb|125px|left|green/yellow ground]] | ||
[[Image:Schutzklasse 1.svg|thumb|60px|right|Class I symbol]] | [[Image:Schutzklasse 1.svg|thumb|60px|right|Class I symbol]] | ||
| − | These appliances must have their chassis connected to | + | These appliances must have their chassis connected to electrical earth (US: ground) by a separate [[earth]] conductor ([[IEC 60446|coloured]] green/yellow (green in the US, Canada and Japan). |
| − | |||
| − | 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 ([[ | + | The earth connection is via a 3-conductor mains flex. 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 if a fault occurs the supply will be removed automatically (this is sometimes referred to as ADS = Automatic Disconnection of Supply). |
| − | 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 | + | |
| + | 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 [[mcb]]) and disconnect the supply. The disconnection time has to be fast enough not to allow heart 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 cuts off the supply of electricity to the appliance if the currents in the two poles of the supply are not equal. | ||
==Class 0I== | ==Class 0I== | ||
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==Class II== | ==Class II== | ||
[[Image:Double insulation symbol.svg|thumb|60px|right|Class II symbol]] | [[Image:Double insulation symbol.svg|thumb|60px|right|Class II symbol]] | ||
| − | A Class II or '''double insulated''' | + | A Class II or '''double insulated''' electrical appliance is one which 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 | + | 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 two layers of insulating material surrounding live parts or by using reinforced insulation. |
| − | + | A double insulated appliance should be labelled ''Class II'' or ''double insulated'' or bear the double insulation symbol (a square inside another square). | |
| − | Insulated | + | Insulated power supplies (eg wallwarts, phone chargers) are typically designed 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 III== | ==Class III== | ||
[[Image:Schutzklasse 3.svg|thumb|60px|right|Class III symbol]] | [[Image:Schutzklasse 3.svg|thumb|60px|right|Class III symbol]] | ||
| − | A Class III appliance is designed to be supplied from a separated/safety 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. For medical devices, compliance with Class III is ''not'' considered sufficient protection, and further more-stringent regulations apply to such equipment. | + | A Class III appliance is designed to be supplied from a separated/safety 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. |
| + | |||
| + | For medical devices, compliance with Class III is ''not'' considered sufficient protection, and further more-stringent regulations apply to such equipment. | ||
==See also== | ==See also== | ||
| − | * [[ | + | * [[Plug]] |
| − | * [[Electricity]] | + | * [[Electricity basics]] |
* [[Portable appliance testing]] | * [[Portable appliance testing]] | ||
| − | |||
==References== | ==References== | ||
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* BS 2754 : 1976 (1999): Memorandum. Construction of electrical equipment for protection against electric shock. | * BS 2754 : 1976 (1999): Memorandum. Construction of electrical equipment for protection against electric shock. | ||
| − | + | [[Category:Electrical]] | |
| − | [[Category: | + | [[Category:Basics]] |
| − | [[Category: | ||
This article (c) CCASA3 [http://en.wikipedia.org/wiki/Appliance_classes wiki] [http://en.wikipedia.org/wiki/Wikipedia:Text_of_Creative_Commons_Attribution-ShareAlike_3.0_Unported_License CCASA] | This article (c) CCASA3 [http://en.wikipedia.org/wiki/Appliance_classes wiki] [http://en.wikipedia.org/wiki/Wikipedia:Text_of_Creative_Commons_Attribution-ShareAlike_3.0_Unported_License CCASA] | ||
Revision as of 12:54, 8 May 2014
In the electrical appliance manufacturing industry, the following IEC protection classes are used to differentiate between the protective earth connection requirements of appliances.
Class 0
These appliances have no protective earth connection and feature only a single level of insulation and were intended for use in dry areas. A single fault could cause an electric shock or other dangerous occurrence. Sales of these items have been banned in the UK since 1975.
Class I
These appliances must have their chassis connected to electrical earth (US: ground) by a separate earth conductor (coloured green/yellow (green in the US, Canada and Japan).
The earth connection is via a 3-conductor mains flex. 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 if a fault occurs the supply will be removed automatically (this is sometimes referred to as ADS = Automatic Disconnection of Supply).
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 mcb) and disconnect the supply. The disconnection time has to be fast enough not to allow heart 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 cuts off the supply of electricity to the appliance if the currents in the two poles of the supply are not equal.
Class 0I
Electrical installations where the chassis is connected to earth with a separate terminal.
Class II
A Class II or double insulated electrical appliance is one which 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 two layers of insulating material surrounding live parts or by using reinforced insulation.
A double insulated appliance should be labelled Class II or double insulated or bear the double insulation symbol (a square inside another square).
Insulated power supplies (eg wallwarts, phone chargers) are typically designed 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 III
A Class III appliance is designed to be supplied from a separated/safety 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.
For medical devices, compliance with Class III is not considered sufficient protection, and further more-stringent regulations apply to such equipment.
See also
References
- 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.