Circuit Breaker for Fire Pump gen set

[sceepe]

Here's the scenario: stand by generator which feeds a Fire pump and also the emerg lighting for the building. Is there a requirement for the generator to have 2 main line circuit breakers? Where in the code?

FYI:I have sized the single generator circuit breaker to be the smallest breaker that will carry between 125% and 250% of the (fire pump full load current + emerg lighting load) and will allow locked rotor current for 20+ seconds.

Thanks in advance

 

[nvcape]

Re: Circuit Breaker for Fire Pump gen set

Look at NEC 695.4. It states that the supply conductors of the fire pump connect to either a listed fire pump controller or listed COMBINATION fire pump controller and power transfer switch. For the generator side, you can use standard motor overcurrent protection, but I can't find any exception to the locked rotor requirement on the normal side. 695 also says that you need enough generator capacity for normal starting and running while supplying the other loads. You are probably better off with 2 output breakers on the generator, but I don't see any restriction on tapping the wires from a single breaker to the two transfer switches. You need to double check and be sure that the generator will handle the large inrush and also that the circuit breaker will not trip.

 

[sceepe]

Re: Circuit Breaker for Fire Pump gen set

Thanks nvcape,
Thats what I was thinking. I size the generator with manufacture's software that takes into account inrush, soft start, and voltage drop considerations.

As for the two breakers in the generator, the only reason I can come up with for having two is that you may need to isolate the generator for maintenance while keeping the emergency lighting system in operation. This assumes that you don't have an optional disconnect as allowed by 695.4.B.

Thanks again,