SIRIUS 3RU2/3RB3 overload relays
5.4 Functions
SIRIUS Innovations
System Manual, 01/2011, A8E56203870002-03
499
5.4.2 Ground-fault protection (3RB31 only)
Introduction
In addition to current-dependent protection for loads against impermissibly high temperature
rise caused by overload, phase asymmetry, and phase failure, 3RB31 solid-state overload
relays feature internal ground-fault detection (not possible in conjunction with contactor
assemblies for star-delta (wye-delta) start). This provides protection of loads against high-
impedance faults to ground caused by damaged insulation, moisture, condensation, etc.
Ground-fault protection
In the event of a ground fault, the device trips immediately, disconnecting the contactor (and
thus the load) by means of the auxiliary contacts. To also protect the load and the system
against ground faults caused by damaged insulation, moisture, condensation, etc., the
overload relays support ground-fault monitoring by means of internal ground-fault detection.
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- 6 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
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