Configuration
6.2 Overload relays in motor feeders
SIRIUS Innovations - SIRIUS 3RU2 thermal overload relays / SIRIUS 3RB3 solid-state overload relays
Manual, 09/2014, A5E03656507420A/RS-AA/002
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Contactor assembly for star-delta (wye-delta) start
Overload relays in contactor assemblies for star-delta (wye-delta) start
When using overload relays in conjunction with contactor assemblies for star-delta (wye-
delta) start, you need to bear in mind that only 1/√3 times the motor current flows through the
line contactor. An overload relay mounted onto a line contactor has to be set to this 0.58-
times motor current.
Note
Internal ground-fault detection on the 3RB31
If you are using the 3RB31 solid-state overload relay in conjunction with contactor
assemblies for star-delta (wye-delta) start, internal ground-fault detection must not be
activated due to the occurrence of transient current peaks when switching over from star
(wye) to delta operation. These current peaks can cause an unintentional response of the
ground-fault monitoring.
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