b Electrical protection
b Safe isolation from live parts
b Local or remote switching
National and international standards define the manner in which electric circuits of
LV installations must be realized, and the capabilities and limitations of the various
switching devices which are collectively referred to as switchgear.
The main functions of switchgear are:
b Electrical protection
b Electrical isolation of sections of an installation
b Local or remote switching
These functions are summarized below in Figure H .
Electrical protection at low voltage is (apart from fuses) normally incorporated in
circuit-breakers, in the form of thermal-magnetic devices and/or residual-currentoperated
tripping devices (less-commonly, residual voltage- operated devices
- acceptable to, but not recommended by IEC).
In addition to those functions shown in Figure H1, other functions, namely:
b Over-voltage protection
b Under-voltage protection
are provided by specific devices (lightning and various other types of voltage-surge
arrester, relays associated with contactors, remotely controlled circuit-breakers, and
with combined circuit-breaker/isolators… and so on)

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