Functions
5.2 Ground fault protection in the case of the 3RB31
SIRIUS Innovations - SIRIUS 3RU2 thermal overload relays / SIRIUS 3RB3 solid-state overload relays
Manual, 09/2014, A5E03656507420A/RS-AA/002
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5.2
Ground fault protection in the case of the 3RB31
Introduction
In addition to the current-dependent protection of loads against impermissibly high
temperature rise resulting from overload, 3RB31 solid-state overload relays offer ground-
fault protection.
Ground-fault protection
A ground fault can arise as a result of insulation damage or ingress of moisture or
condensate. This results in displacement of the neutral point voltage of the power network,
and in an unbalance. The neutral point voltage is simulated virtually in the device and when
a neutral point displacement voltage arises, the overload relay switches the contactor off
instantaneously. This prevents thermal follow-on damage and a resulting, and significantly
more critical, double ground fault.
Note
Contactor assembly for star-delta (wye-delta) start
Internal ground-fault detection is not possible with contactor assemblies star-delta (wye-
delta) start.
Table 5- 3
Ground-fault detection
Type of ground-fault detection
Application
Internal ground-fault detection
For motors with three-wire connection for the detection of fault
currents ≥
75 % of the current setting I
e
in operation
Reference
More information ...
can be found in the Chapter ...
about ground-fault protection of the solid-state
overload relays in conjunction with star-delta
(wye-delta) assemblies
Contactor assembly for star-delta (wye-delta)