Schneider Electric - Electrical installation guide 2009
H
© Schneider Electric - all rights reserved
Chapter H
LV switchgear: functions &
selection
Contents
The basic functions of LV switchgear
H2
1.1 Electrical protection
H2
1.2 Isolation
H3
1.3 Switchgear control
H4
The switchgear
H5
2.1 Elementary switching devices
H5
2.2 Combined switchgear elements
H9
Choice of switchgear
H0
3.1 Tabulated functional capabilities
H10
3.2 Switchgear selection
H10
Circuit-breaker
H
4.1 Standards and description
H11
4.2 Fundamental characteristics of a circuit-breaker
H13
4.3 Other characteristics of a circuit-breaker
H15
4.4 Selection of a circuit-breaker
H18
4.5 Coordination between circuit-breakers
H22
4.6 Discrimination MV/LV in a consumer’s substation
H28
2
3
4
Schneider Electric - Electrical installation guide 2009
H - LV switchgear: functions & selection
H2
© Schneider Electric - all rights reserved
The basic functions of
LV switchgear
The role of switchgear is:
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-current-
operated 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 v