Disable G of LSIG and use earth leakage relay 2

[NickParker]

We have a LV switchgear where in the Incoming breaker, there is a trip unit which is of LSIG and also have a separate earth leakage relay.

Is it okay to disable the G function of the trip unit and use only earth leakage relay for earth/ground faults?

The reason is the G function cannot be set for low pickup, that is at 5A, while the spec calls to trip at 5A for ground faults in hazardous area.

 

[DaSnipeKid]

@NickParker.
You can disable the G function of the LSIG. But make sure that the earth leakage relay that you are intending to use should be wired to the shunt trip (or likewise) of your incomer. This will ensure that if 5A of the current flows through the earth circuit, the shunt trip will open the incomer.

Danke,
DaSnipeKid.

 

[dpc]

It might not be possible to disable the ground function - it will depend on the trip unit. But if the earth leakage protection is more sensitive than the lowest setting of the Ground function, I don't see any issue.

 

[che12345]

Mr NickParker (Electrical)(OP)15 May 23 09:15
" ....a LV switchgear where in the Incoming breaker, there is a trip unit which is of LSIG and also have a separate earth leakage relay.
#1.Is it okay to disable the G function of the trip unit and use only earth leakage relay for earth/ground faults?
#2. The reason is the G function cannot be set for low pickup, that is at 5A, while the spec calls to trip at 5A for ground faults in hazardous area".
1. Yes. You may switch off the G function.
2. Attention:
a) The breaker with LSIG is NOT installed with a UV or shunt release. You would have to order the breaker with a UV or shunt release and wire it separately to the earth leakage relay.
b) to trip G-fault a 5A with/without time delay is considered too sensitive for a breaker say >1kA. Unwanted tripping may result! Clarify the specification.
c) for 5A detection, you need a zero-sequence CT with big window for big number of LV cables. Do NOT use four CTs summation configuration.
Che Kuan Yau (Singapore)