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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
close this folder2. Important components of switches
View the document2.1. Switching contacts
View the document2.2. Arcs
View the document2.3. Switch mechanisms
close this folder3. Low-voltage circuit breakers
View the document3.1. Classification and tasks of the circuit breakers
close this folder3.2. Circuit breakers
View the document(introduction...)
View the document3.2.1. Universal circuit breakers
View the document3.2.2. Compact circuit breakers
View the document3.2.3. High-speed switches for d.c. installations
View the document3.2.4. Protective switches
close this folder3.3. Overload circuit breakers
View the document(introduction...)
View the document3.3.1. Multisection cam-operated switches
View the document3.3.2. Contactors
close this folder3.4. On -load switches
View the document(introduction...)
View the document3.4.1. Load-break switches in slim design
View the document3.4.2. Installation switcher
View the document3.5. Off-load switches
close this folder4. Relays and control devices
close this folder4.1. Relays
View the document(introduction...)
View the document4.1.1. Neutral or auxiliary relays
View the document4.1.2. Time relays
View the document4.1.3. Undervoltage and overvoltage relays
View the document4.1.4. Overcurrent relays
View the document4.1.5. Overcurrent time relays
View the document4.1.6. Magnetic overcurrent relays
View the document4.1.7. Signal relays
close this folder4.2. Control devices
View the document4.2.1. Discrepancy switches
View the document4.2.2. Control discrepancy switches

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.