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close this bookSwitchgear - Basic vocational knowledge (Institut für Berufliche Entwicklung, 54 p.)
View the document(introduction...)
View the documentPreface
View the document1. General remarks
Open this folder and view contents2. Important components of switches
Open this folder and view contents3. Low-voltage circuit breakers
Open this folder and view contents4. Relays and control devices

1. General remarks

Low-voltage switchgear has to fulfil mainly the following functions in electrical energy systems:

- disconnecting
- switching (in the sense of arbitrary switching)
- protecting and
- limiting of the short-circuit current.

Since the field of application of low voltage is very extensive, there is a large variety of low-voltage switchgear.


Switches are devices for opening and closing electric circuits in which all parts necessary for connecting or disconnecting are mounted firmly on a joint base.


Relays are devices which are influenced by the change of physical magnitudes and control electrically further devices.


Trips are devices which are influenced by the change of physical magnitudes and control mechanically further devices.


Regulators are devices provided with resistances for changing the operating state of electric operating means whose resistance remains permanently switched on in the circuit.

Plug-and-socket connectors

Plug-and-socket connectors are devices for establishing connections of current paths without additional auxiliary means, with connection for electric supply lines.


Fuses are devices for interrupting current paths by melting of a piece of fusible metal when a current is exceeded in a given period of time. The fuse comprises all components of which the complete device consists.