Fire Pump Question

[Cardinal]

I am considering installing a non-fused disconnect switch on a fire pump circuit ahead of the pump controller but before the power source. The fire pump is 250 Hp and the jockey pump is 7.5 HP. Looking at NEC 695, it appears i need a 2000 amp disconnect! I am thinking that this only really applies to the overcurrent protection calculation. Since i have a non-fused disconnect, can i just size the safety switch to the combined motor HP? Do i need overcurrent protection?

The reason i want to do this is to allow our techs to service the fire pump controller and jockey pump controller without having to kill the main 480 volt transformer, which basically kills the plant. The existing configureation has the feeder cables for the fire pump and jockey pump coming directy off of the secondary of a 2500 KVA transformer. The arc flash rating is off the charts and we want to avoid any work at all with the power on but dont want to shut the plant down.

 

[wsbeih]

I am considering installing a non-fused disconnect switch on a fire pump circuit ahead of the pump controller but before the power source. The fire pump is 250 Hp and the jockey pump is 7.5 HP. Looking at NEC 695, it appears i need a 2000 amp disconnect! I am thinking that this only really applies to the overcurrent protection calculation. Since i have a non-fused disconnect, can i just size the safety switch to the combined motor HP?




The reason i want to do this is to allow our techs to service the fire pump controller and jockey pump controller without having to kill the main 480 volt transformer, which basically kills the plant. The existing configureation has the feeder cables for the fire pump and jockey pump coming directy off of the secondary of a 2500 KVA transformer. The arc flash rating is off the charts and we want to avoid any work at all with the power on but dont want to shut the plant down.

I would be careful with using unfused switch. The available short circuit will be too high (as you are tapping directly from 2500kVA transformer) for unfused switch SCCR.
IMO, you would need two local fused disconnects for each motor sized per article 430. As for the fire pump motor disconnect you will need to comply with 695.4(B)

 

[GoldDigger]

I would be careful with using unfused switch. The available short circuit will be too high (as you are tapping directly from 2500kVA transformer) for unfused switch SCCR.
IMO, you would need two local fused disconnects for each motor sized per article 430. As for the fire pump motor disconnect you will need to comply with 695.4(B)

With tongue firmly in cheek I suggest a set of 2000A fuses to reduce the fault current followed by a smaller series-rated unfused disconnect. :angel:

 

[gadfly56]

I would be careful with using unfused switch. The available short circuit will be too high (as you are tapping directly from 2500kVA transformer) for unfused switch SCCR.
IMO, you would need two local fused disconnects for each motor sized per article 430. As for the fire pump motor disconnect you will need to comply with 695.4(B)

Not here. You need to use the locked rotor current for the fire pump and the pressure maintenance pump; NFPA 70-2014 695.4(B)(2).

 

[gadfly56]

With tongue firmly in cheek I suggest a set of 2000A fuses to reduce the fault current followed by a smaller series-rated unfused disconnect. :angel:

Well, OK, but you only get one disconnecting means allowed in this case [NFPA 70-2014 694.(B)(1)], unless you claim you need it to comply with 695.3(C)