Fire Pump Service ratings

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websparky

Senior Member
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Cleveland, Ohio
I am reviewing a fire pump service. The pump motor is 25 hp. 480V 3 phase.
I am trying to determine the proper size conductors from the service mast through to the motor.
When I look at 695.6(C)(2), and follow it to 430.22 which refers me to 430.6(A)(1) which refers me to Table 430.250.
There I find 34A to be the full load rating. That times 1.25% equals 42.5A.
Then I read 183A locked rotor in Table 430.251(B).

So if I understand this correctly, the service conductors could be rated at 100A minimum.
The main disconnect breaker must be rated at 200A minimum.
The branch circuit breaker must also be rated at 200A minimum.
The conductors going to the moter controller and motor could be rated at 50A.

Am I reading this correct??

Thanks!
 
Re: Fire Pump Service ratings

The conductors must be rated 125% of the FLA of the equipment. You do not normally install a main disconnect with over current protection at the service. The OC protection is located at the fire pump and is part of the fire pump control equipment.
Check this sihttp://www.ecmweb.com/mag/electric_code_basics_17/te for more information.

[ November 08, 2005, 11:08 PM: Message edited by: bob ]
 
Re: Fire Pump Service ratings

You can install a service disconnect, but it must be rated to carry locked rotor current. For a 100 hp 460V motor, that would be an 800 ampere device.

But fire pump conductors have to be sized for voltage drop, this is the only place in the code where voltage drop compliance is required.
 
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