Rockwell Automation Low-Voltage Switchgear and Controlgear - Manual (Page 64)

ƒ Switching-over of supply systems (for example for standby power supplies), for which
complete separation of the two supply systems is required.
ƒ Switching of several single-phase loads (heaters, lamps) with one switchgear unit.
ƒ Switching direct current loads with higher rated voltage that requires the series connection of
four contacts (see also Section 2.4.2 ).
2.4.4.2 Applications of switchgear with 2 NO and 2 NC contacts
Devices with two NO and two NC contacts are useful in applications in which one of two circuits
must always be closed. These are, for example
ƒ Switching a heater between two levels (
Fig. 2.4-7 )
ƒ Switching-over between single-phase supplies – for example, emergency power supply
systems ( Fig. 2.4-7 )
ƒ Reversing motors for space saving arrangement of devices ( Fig. 2.4-8 )
ƒ Reversing of 2-step motors with separated windings ( Fig. 2.4-9 )
1 2
Fig. 2.4-7
Four-pole contactors with 2 NO / 2 NC contacts for switching single-phase loads (left) or switching-over
between two supplies (right)
M
3~
I >
L1 L2 L3
V
I / O
Fig. 2.4-8
Slimline reversing starter with a 2 NO / 2 NC contactor for reversing
LVSAM-WP001A-EN-P - April 2009 2-36