Protection classes

PROTECTION CLASS I / PROTECTIVE EARTH / EARTHING

All electrically conductive housing parts of the equipment are connected to the protective conductor system of the fixed electrical installation, which is at earth potential. Movable equipment of protection class I has a plug connection with protective earth contact, a plug with protective contact or, in Switzerland, a three-pin plug. The protective earth connection is designed in such a way that it is the first to be made when the plug is plugged in and the last to be disconnected in the event of damage (see leading contact). The insertion of the connecting cable into the unit must be mechanically strain-relieved; when the cable is torn out, the protective conductor must be the last to break off.

If, in the event of a fault, a current-carrying conductor touches the enclosure connected to the protective conductor, a short circuit to the body usually occurs so that the miniature circuit breaker (fuse) or a residual current circuit breaker trips and switches the circuit voltage-free

PROTECTION CLASS II /
PROTECTIVE INSULATION

Equipment with protection class II has reinforced or double insulation between the mains circuit and the output voltage or metal housing (VDE 0100 Part 410, 412.1). They usually have no connection to the protective earth conductor. This protective measure is also called protective insulation II (safe electronic separation). Even if they have electrically conductive surfaces, they are protected from contact with other live parts by reinforced insulation. Movable devices of protection class II usually do not have an earthing contact plug; for connection, plugs are used that do not have an earthing contact; for large currents, these are contour plugs in Germany – plug designs that look similar to a Schuko plug.

PROTECTION CLASS III / PROTECTIVE EXTRA-LOW VOLTAGE

Protection class III equipment operates with safety extra-low voltage (SELV/PELV) and also requires reinforced or double insulation between mains circuits and the output voltage during mains operation. Devices that generate safety extra-low voltage (SELV/PELV), i.e. voltages not exceeding 50 V AC or 120 V DC from the mains voltage, require a safety transformer according to DIN VDE 0570-2-6 or EN 61558-2-6.