Fire Pump Conductors

[Sean.Day72]

I want to confirm my understanding of Art. 695. I'm sizing my POWER SOURCE i.e POCO transformer to hold the locked rotor current of the fire pumps, plus jockey maintenance pump, plus ancillary equipment i the pump house. However the conductors feeding the motors are sized per Art. 430 at no less than 125%. So if there is a locked rotor event the transformer will hold the increased current, but eventually the motor and/or the conductors will melt. Are the secondary conductors from utility transformer sized off of "normal" calculation based Art. 220 & 430 calculated to 208A or sized to hold the 1158A based off of Locked rotor current?

Here is my scenario:

150HP Fire Pump = Locked Rotor Current of 1123A (Art 430 Full load amps= 180A)
1.5HP Jockey Pump = Locked Rotor Current of 10.2A (Art. 430 Full load amps= 3A )
Ancillary Loads = 25 Amps
Total Lock Rotor + Ancillary Loads = 1158.2A (961KVA)
Full Load Currents + Ancillary Loads = 208A

 

[texie]

I want to confirm my understanding of Art. 695. I'm sizing my POWER SOURCE i.e POCO transformer to hold the locked rotor current of the fire pumps, plus jockey maintenance pump, plus ancillary equipment i the pump house. However the conductors feeding the motors are sized per Art. 430 at no less than 125%. So if there is a locked rotor event the transformer will hold the increased current, but eventually the motor and/or the conductors will melt. Are the secondary conductors from utility transformer sized off of "normal" calculation based Art. 220 & 430 calculated to 208A or sized to hold the 1158A based off of Locked rotor current?

Here is my scenario:

150HP Fire Pump = Locked Rotor Current of 1123A (Art 430 Full load amps= 180A)
1.5HP Jockey Pump = Locked Rotor Current of 10.2A (Art. 430 Full load amps= 3A )
Ancillary Loads = 25 Amps
Total Lock Rotor + Ancillary Loads = 1158.2A (961KVA)
Full Load Currents + Ancillary Loads = 208A

The conductors are NOT sized to locked rotor current. Pump and jockey at 125% plus other loads. See 695.6(B).

 

[ces]

I want to confirm my understanding of Art. 695. I'm sizing my POWER SOURCE i.e POCO transformer to hold the locked rotor current of the fire pumps, plus jockey maintenance pump, plus ancillary equipment i the pump house. However the conductors feeding the motors are sized per Art. 430 at no less than 125%. So if there is a locked rotor event the transformer will hold the increased current, but eventually the motor and/or the conductors will melt. Are the secondary conductors from utility transformer sized off of "normal" calculation based Art. 220 & 430 calculated to 208A or sized to hold the 1158A based off of Locked rotor current?

Here is my scenario:

150HP Fire Pump = Locked Rotor Current of 1123A (Art 430 Full load amps= 180A)
1.5HP Jockey Pump = Locked Rotor Current of 10.2A (Art. 430 Full load amps= 3A )
Ancillary Loads = 25 Amps
Total Lock Rotor + Ancillary Loads = 1158.2A (961KVA)
Full Load Currents + Ancillary Loads = 208A

I haven't done a fire pump in some time but a while back I did lots of them in Southern California and I would like to offer a couple of thoughts for consideration. This is my understanding but perhaps someone has more up to date info on this?
1) fire pump circuit breakers are special breakers, I believe as it happens they are 400% rated, and have specific trip characteristics.
2) again I haven't design one of these recently but normally a fire pump is fed from a tap that is ahead-of-the-main. and the jockey pump is not on this tap. The fire pump is isolated from other building loads, so that a fault that would take down a building main disconnect will not disrupt fire pump power. I never saw an exception to this. But all together I see the load calc as being FP=180FLA @125%, JP=3FLA @100%, and ancillary =25A +25% of ancillary long continuous loads such as lighting.
3) the locked rotor depends on the code letter of the motor. I've always requested nameplate from the fire protection engineer or contractor. As I recall they were Code G (6.29x) more often than not. See Table 430.7(B) Locked-Rotor Indicating Code Letters. However as already responded wiring is not sized to locked rotor. From memory the only reason I even asked for it was for generator sizing but it can also be an input into software such as SKM Power tools.

There must be other threads that have already flushed this out...

 

[Sean.Day72]

Ok 695.3 "power source has to indefinitely carry the locked rotor current" really threw me off. I mistakenly thought "power source" meant the utility transformer. By power source I think they mean the Medium Voltage side of the utilities power grid, not the utilities step down transformer itself. I'm running directly from the Utilities transformer to a listed fire pump controller assembly w/ no OCPD in between. If OCPD was in between the service and the fire pump controller it would be sized to hold LRC. So I size the conductors to 125% of all the Full load currents and the utility transformer sized to carry all the load of the building plus %125 of the fire pump load.

I like to think logical.. so in a worst case LRC event either the motor winding will fail or the conductors feeding the Fire Pump controller will fail, we just don't want a breaker opening prematurely during a life safety event. The OCPD integral to the listed fire pump controller is sized to LRC so it might open before the conductors and/or motor fails?