Fire pump ground protection - NEC 695.6(G) 1

[chuckd83]

NEC 695.6(G) states "Ground-fault protection of equipment shall not be installed in any fire pump power circuit."

Does this include upstream ground-fault protection all the way to the transformer? This would remove ground-fault protection from all other equipment fed from the substation. Or is it only the circuit the fire pump is on?

 

[cuky2000]

NEC 695 INTENT & GENERAL DESIGN PHILOSOPHY: The intent of the NEC regarding fire pump operation is to save the facility kipping the fire pump in service, without tripping the protection system even if doing damages or destruction of the pump. Considering that, ground-fault protection of equipment is not allowed per NEC 695.6(G).


In addition to proper setting the upstream ground-fault protection, provisions for multiple sources with the capacity to carry the locked-rotor current of the fire pump motor(s) must be considered including a separate electric utility service and/or on-site standby generators.

I hope other colleagues bring more light to this subject.

 

[RRaghunath]

cuky2000, I too have faced this issue.
Once the incomer is set earth fault protection and standby earth fault protection (connected to transformer neutral CT), the incomer is going to trip for an uncleared fault in the Fire pump feeder downstream.
I wonder how the said clause in NEC will enhance the security of fire water supplies.
Could the idea be to give more time for the pump for the earth fault current magnitude to increase to the level of earth fault protection pickup setting in the incomer??
The same stipulation is there in NFPA for HV motors as well and as we all know, the earth fault current can increase rapidly in HV systems if the faulty feeder is not isolated.

 

[chuckd83]

Thanks for the replies. I think you’re right the the entire substation cannot trip for a ground fault. Maybe a possible solution is to make it high resistance grounded.

 

[dpc]

The supply for the fire pump should come from a separate service. So yes, this precludes GF protection anywhere that could cause loss of the power to the fire pump.

 

[RRaghunath]

dpc, Thanks for the response.
By 'separate source', do you mean a dedicated transformer to feed the fire pump??
This way the neutral can be high resistance earthed with alarm (only) on earth fault.

 

[dpc]

This could be a separate transformer, but could also simply be a separate low side tap from the transformer that is ahead of the main building supply. So it essentially a separate service from the same transformer. So a ground fault trip on the main service would not interrupt service to the fire pump.