Fire Pump Power Supply Configuration
Fire Pump Power Supply Configuration
(OP)
Hi everyone,
The reason I am consulting you is to ask if you know if there is any limitation or restriction given by NFPA 20 or NFPA 70 (NEC) for the power supply configuration of an electrical driven fire pump; I mean if it matters if it is Wye solidly grounded or Wye grounded with a NGR.
I have read these two standards and I have not found anything but I am not 100% sure.
In our design there is a 460 V 250 hp motor (fire pump) and a 460 V 5 hp (jockey pump) fed from a 1250 kVA 13.8/0.48 kV transformer Delta-Wye. The question will be if it matters if the Wye side is solidly gorunded or limited through a 5 A NGR - is there anything that rules this? In any case a ground fault protection will not be installed as per NFPA requirements.
Thanks and regards,
The reason I am consulting you is to ask if you know if there is any limitation or restriction given by NFPA 20 or NFPA 70 (NEC) for the power supply configuration of an electrical driven fire pump; I mean if it matters if it is Wye solidly grounded or Wye grounded with a NGR.
I have read these two standards and I have not found anything but I am not 100% sure.
In our design there is a 460 V 250 hp motor (fire pump) and a 460 V 5 hp (jockey pump) fed from a 1250 kVA 13.8/0.48 kV transformer Delta-Wye. The question will be if it matters if the Wye side is solidly gorunded or limited through a 5 A NGR - is there anything that rules this? In any case a ground fault protection will not be installed as per NFPA requirements.
Thanks and regards,






RE: Fire Pump Power Supply Configuration
As you said "in any case a ground fault protection will not be installed" .The both motors have to be delta connected and no grounding.
The wye side of the transformer may be grounded in order to limit the undamaged phase's voltage to ground but as no ground protection will be provided a suitable resistance has to be inserted between neutral point and ground in order to limit the fault current .The non live metallic parts of the motor will be grounded.
RE: Fire Pump Power Supply Configuration
I have always seen and specified grounded sources.
RE: Fire Pump Power Supply Configuration
I would never implement HRG on any 480 V system in a commercial building. Only industrial facilities with an in-house electrical maintenance crew.
And never never ever use **low-resistance** grounding at 480 V.
"The more the universe seems comprehensible, the more it also seems pointless." -- Steven Weinberg
RE: Fire Pump Power Supply Configuration
If there's no bond between the motor star point and the system neutral or earth, which would be the case in any normal star-connected motor, why would this matter? I'm curious because I see the occasional NFPA-compliant system destined for an overseas plant and wonder if I've been overlooking something during design review.
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If we learn from our mistakes I'm getting a great education!
RE: Fire Pump Power Supply Configuration
RE: Fire Pump Power Supply Configuration
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If we learn from our mistakes I'm getting a great education!