I'm trying to make sure I understand Article 695.4 and 695.6. The way I understand it, the overcurrent protection is sized based on the locked-rotor current, however the feeder is only sized on 125% of the FLA. Hypotheticaly if you had a 40HP fire pump you could have #4 CU on a 300 amp breaker? My second question would be if this is served from the utility transformer how would you have to size the direct wire meter socket. 100 amps based on 125% of FLA or 300 amp based on LRC. This is not based on an actual situation, just trying to understand.
Fire pump - please confirm
- Thread starter shockin
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charlie
Senior Member
- Location
- Indianapolis
Let's make this easy.
Everything is set up the same as any other motor . . . except for the overcurrent device. The motor will fail before any of the circuit components that feed the motor and that is desired. If overcurrent protection is provided, the protection is for short circuits and ground faults only, not overload protection. You are correct, it will look funny but that is because we want every drop of water that can be pumped to be pumped before the motor fails completely. A listed fire pump motor controller will actually drop the motor after 22 seconds (I think) of locked rotor. :smile:
Everything is set up the same as any other motor . . . except for the overcurrent device. The motor will fail before any of the circuit components that feed the motor and that is desired. If overcurrent protection is provided, the protection is for short circuits and ground faults only, not overload protection. You are correct, it will look funny but that is because we want every drop of water that can be pumped to be pumped before the motor fails completely. A listed fire pump motor controller will actually drop the motor after 22 seconds (I think) of locked rotor. :smile:
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
No, a FIRE PUMP controller will not drop out on locked rotor overload at all, but a "regular" pump controller might. The concept, as you correctly identified in the first part of your response, is "run to destruction". In other words, sacrifice the pump motor, save the building.charlie said:
The "22 seconds" at locked rotor (actually it would be 20 seconds) would be the definition of a Class 20 OL Relay. 10 seconds is the definition of Class 10. But again, fire pump controllers would not have any OL relay at all.
Thanks for the responses I thought I was on the right track. How about the question about metering in the OP. IMO a direct wire meter would have to be sized based on the LRC so its not the weakest link. Then again if its only feeding the fire pump, and not the jockey pump, then maybe the POCO dosen't require metering since it will hopefully never run. Thoughts?
charlie
Senior Member
- Location
- Indianapolis
We require a cash register to be installed for any power connection with a very few exceptions that involve public safety. The meter fitting is just like the rest of the circuit for any other motor, a fire pump motor is not special except for the overcurrent selection.shockin said:
You may run into a situation where you have to oversize your service in order to accommodate the overcurrent device. Then the serving electric utility representative (who doesn't understand fire pump installations) will tell you that he wants a huge meter fitting or a CT cabinet for a small service. It really gets sticky when the person that is looking at the installation doesn't understand it.
charlie said:
You don't have a service called "unmetered service?" AEP does for many situations (like street lights and remote cable tv amplifiers), I'm sure it's priced to be more than it would have been if you just got a meter. Might be a new profit center for your utility!
Pierre C Belarge
Senior Member
- Location
- Westchester County, New York
arnolds said:
What reference in the NEC did you see that in?
maybe a local thing, but the last time I got involved with a fire pump, the Fire marshall would not allow any disconnect whatsoever. (NFPA 20 ??).
As I understand, although NEC 695.4 allows a disconnect/overcurrent, it does not require one. The fire pump controllers installed in this area are "service rated" and the installations I have seen are designed so that the service conductors feed directly to the pump controller.
As I understand, although NEC 695.4 allows a disconnect/overcurrent, it does not require one. The fire pump controllers installed in this area are "service rated" and the installations I have seen are designed so that the service conductors feed directly to the pump controller.
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