Protection class (electrical engineering)

In electrical engineering, protection classes are used to classify and identify electrical equipment (e.g. devices and installation components) in relation to the existing safety measures to prevent an electric shock .

General

The protection classes for all electrical equipment are specified in EN 61140 (Germany: VDE 0140-1).

There are four protection classes for electrical equipment, with only protection classes one to three being permitted in the EU and other industrialized countries. To identify the equipment with the relevant protection class, symbols are provided, which are defined in IEC 60417. The use of protective measures in the various classes of electrical equipment is described in EN 61140 (Germany: VDE 0140-1): 2007-03, Section 7.

The protection class must be differentiated from the protection class classified with IP (Ingress Protection according to IEC 60529) . While protection classes define measures that protect against dangerous contact voltages, the IP protection classes describe the degree of protection of the housing against contact, foreign bodies and water.

Protection class 0

Besides the basic insulation, there is no special protection against electric shock . Connection to the protective conductor system is not possible. Protection is only to be ensured by the environment of the equipment. There is no symbol for protection class 0; labeling is not provided. It should also no longer be included in the future international standard. However, it is still used in some countries. It is not used in Germany.

Protection class I / protective conductor

Earth symbol (for protection class I)

All electrically conductive housing parts of the equipment are connected to the protective conductor system of the fixed electrical installation , which is at ground potential . Mobile devices of protection class I have a plug connection with a protective conductor contact or a cable with an additional protective conductor and a protective contact plug. The protective conductor connection is designed in such a way that it is established first when the plug is inserted and last disconnected when it is pulled out (see leading contact ). In addition to the mechanical strain relief, the connection cable must be introduced into the device in such a way that the protective conductor is torn off last when the cable is torn out.

If z. As a current-carrying conductor erroneously touches the housing connected to the protective conductor, creating a body contact . The protective conductor connection of the housing is dimensioned in such a way that there is no permanent dangerous contact voltage on the housing and that the line circuit breaker (fuse) or an earth leakage circuit breaker trips within a short time and disconnects the circuit from the power supply.

The symbol on the right stands for the earthing that takes place with protection class I. There is no symbol for protection class I itself.

Protection class II / protection through double or reinforced insulation

Symbol protection class II

Equipment with protection class II has reinforced or double insulation equal to the rated insulation voltage between active and accessible parts (VDE 0100 part 410, 412.1). They usually have no connection to the protective conductor . If they have an electrically conductive surface or conductive touchable parts, these are separated from live parts by reinforced or double insulation and have a contact current that does not exceed 0.5 mA.

To connect mobile devices of protection class II, plugs are mostly used that do not have a connection for the protective conductor and no protective conductor; For large currents, these are contour plugs in Germany and Austria , and T11 or T21 plugs in Switzerland . For small currents (up to 2.5 A), Euro plugs are used in these three countries .

If a cable with a protective conductor is used, it must not be connected to the housing and must be treated like an active conductor (VDE 0100 part 410, 412.2.2.4). Example: Industrial vacuum cleaner with Schuko socket on the device.

Equipment of this protection class must be marked with "protection class II" (see right) (VDE 0100 part 410, 412.2.1.1).

Protection class III / protection through low voltage

Symbol protection class III

Equipment of protection class III works with safety extra-low voltage or protective extra-low voltage (SELV / PELV).

Equipment of protection class III may only be connected to SELV or PELV power sources. These include u. a.

Safety transformer according to DIN EN 61558-2-6 (VDE 0570-2-6).
electrochemical power source ( battery , accumulator )
Solar cell, dynamo, crank generator or similar, which supply a low voltage

Devices with functional extra-low voltage with safe separation (PELV) have reinforced or double insulation between the mains connection and the parts carrying extra-low voltage - the extra-low voltage circuits or housing may, however, be grounded. The reason for earthing is not safety, but electromagnetic compatibility (interference emission, earth loops , ESD protection ); it is a functional earth . Examples are laptop power supplies or audio devices.

literature

DIN EN 61140 (VDE 0140-1): 2007-03 Protection against electric shock - Common requirements for systems and equipment (IEC 61140: 2001 + A1: 2004, modified); German version EN 61140: 2002 + A1: 2006. VDE-Verlag, Berlin
DIN VDE 0100-410 (VDE 0100-410): 2007-06 Installation of low-voltage systems - Part 4-41: Protective measures - Protection against electric shock (IEC 60364-4-41: 2005, modified); German takeover HD 60364-4-41: 2007. VDE-Verlag, Berlin
Werner Hörmann, Bernd Schröder: Protection against electric shock in low-voltage systems - Comment from DIN VDE 0100-410 (VDE 0100-410): 2007-06. VDE series of publications, volume 140. VDE-Verlag, Berlin, ISBN 978-3-8007-3190-9

Individual evidence

^ ^A ^b J. Lienig, H. Brümmer: Electronic device technology - basics for the development of electronic assemblies and devices . Springer Vieweg, 2014, ISBN 978-3-642-40961-5 , pp. 42-43.
↑ DIN VDE 0701-0702: 2008-06 Checks after repairs, changes to electrical devices - Repetitive testing of electrical devices - General requirements for electrical safety . VDE publishing house, Berlin.
↑ DIN EN 61140 (VDE 0140-1)
↑ DIN VDE 0100-410 (VDE 0100-410): 2007-06 Clause 414.3

[SchutzklassenBuch-1] A ^b J. Lienig, H. Brümmer: Electronic device technology - basics for the development of electronic assemblies and devices . Springer Vieweg, 2014, ISBN 978-3-642-40961-5 , pp. 42-43.

[2] DIN VDE 0701-0702: 2008-06 Checks after repairs, changes to electrical devices - Repetitive testing of electrical devices - General requirements for electrical safety . VDE publishing house, Berlin.

[3] DIN EN 61140 (VDE 0140-1)

[4] DIN VDE 0100-410 (VDE 0100-410): 2007-06 Clause 414.3