Functions Performed by Electrical Switchgear

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Functions Performed by Electrical Switchgear (on photo Blokset switchboard withdrawable unitcassette)

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Functions Performed by Electrical Switchgear

Nationaland

international standards define the method for making electrical distribution circuits as well as the purpose andfunctions of switchgear

There are three main functions namely

1 Circuit protection takes three main fault types into account

Overloads

Short-circuits(Both of which adversely affect the lifetime of cables and loads)

Insulation faults harmful for persons and equipment

2 Isolation is used to separate a circuit or a device from the remainder of the installation to allow 100 safeoperation

3 Control allows the user to take voluntary action on installation operation

When such action takes place in normal operating conditions (on load with no overcurrent) in orderto energise or de-energise all or part of the installation control is said to be ldquofunctionalrdquo

When such action is essential (whatever the load condition of the installation) in order to immediatelyde-energise all or part of the installation control is said to be of the ldquoemergency stoprdquo kind

Three main functions of electrical circuits

1 Protection

2 Isolation

3 Control

The switch is used for

1 Control

2 Often isolation

For protection it must be combined with

1 Circuit-breaker

2 Fuses

3 Residual current device (if necessary)

A variety of switchgear perform all or some of these three main functions The following table situates the roleof the main switchgear

Functions perfomed Protections Isolation Control

Switchgear Overloads Short-circuit Insulation-fault

Fuse Yes (3) Yes No No No

Disconnector No No No Yes No

Switch No No Yes (1)(2) Yes Yes

Disconnector ndash fuse Yes Yes No Yes No

Switch ndash fuse Yes Yes Yes (1)(2) Yes Yes


Contactor No No No No Yes

Circuit-breaker Yes Yes Yes (2) Yes Yes

Yes ndash Basic function of the switchgear considered (always performed)Yes ndash Additional function possible (not always performed)

(1) Possible with a switch with automatic opening(2) Possible with addition of a ldquoResidual Current Device (RCD)ldquo(3) gG fuse only

Resource Schneider Electric - Low voltage switches


Overloads

Short-circuits(Both of which adversely affect the lifetime of cables and loads)

Insulation faults harmful for persons and equipment

2 Isolation is used to separate a circuit or a device from the remainder of the installation to allow 100 safeoperation

3 Control allows the user to take voluntary action on installation operation

When such action takes place in normal operating conditions (on load with no overcurrent) in orderto energise or de-energise all or part of the installation control is said to be ldquofunctionalrdquo

When such action is essential (whatever the load condition of the installation) in order to immediatelyde-energise all or part of the installation control is said to be of the ldquoemergency stoprdquo kind

Three main functions of electrical circuits

1 Protection

2 Isolation

3 Control

The switch is used for

1 Control

2 Often isolation

For protection it must be combined with

1 Circuit-breaker

2 Fuses

3 Residual current device (if necessary)

A variety of switchgear perform all or some of these three main functions The following table situates the roleof the main switchgear

Functions perfomed Protections Isolation Control

Switchgear Overloads Short-circuit Insulation-fault

Fuse Yes (3) Yes No No No

Disconnector No No No Yes No

Switch No No Yes (1)(2) Yes Yes

Disconnector ndash fuse Yes Yes No Yes No









Functions Performed by Electrical Switchgear

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