Fire Pump Connection

[faresos]

Hello Everyone,

I'm reviewing a documents where the building and the utilities are owned by the government (it's a military base). the design indicates a unit substation consists of a primary switch gear (34.5KV), transformer (3.75MVA), and low voltage switchgear (6000A @480/277V). The drawing show the power connection to the fire pump is from the secondary side of the transformer via drawout breaker located in a separate vertical section (which I think this is violation of the NEC by feeding the fire pump from an overcurrent protections device). my questions:

1. shouldn't the power source be a head of the main MV switchgear breaker since this consider to be our service disconnect? If so, do we need to have a tap in MV section ahead of the main breaker or we can add another breaker in addition to the main to feed the fire pump?
2. I know the final say will be for the AHJ but can we feed the fire pump from the low voltage section (ahead of the 6000A main breaker)? This will save me from adding another transformer for the fire pump.


Thanks,

 

[gadfly56]

Hello Everyone,

I'm reviewing a documents where the building and the utilities are owned by the government (it's a military base). the design indicates a unit substation consists of a primary switch gear (34.5KV), transformer (3.75MVA), and low voltage switchgear (6000A @480/277V). The drawing show the power connection to the fire pump is from the secondary side of the transformer via drawout breaker located in a separate vertical section (which I think this is violation of the NEC by feeding the fire pump from an overcurrent protections device). my questions:

1. shouldn't the power source be a head of the main MV switchgear breaker since this consider to be our service disconnect? If so, do we need to have a tap in MV section ahead of the main breaker or we can add another breaker in addition to the main to feed the fire pump?
2. I know the final say will be for the AHJ but can we feed the fire pump from the low voltage section (ahead of the 6000A main breaker)? This will save me from adding another transformer for the fire pump.


Thanks,

If the fire pump is feeding a single building then you should think of it as any civilian setup. For a commercial space, are you going to run taps on the line side of the pole pig? No, of course not. The drawout breaker could be OK, the separate vertical section is required (if you're using a section at all). The breaker needs to be rated for the locked rotor current of the fire pump, as does the MV breaker. Although, come to think of it, it really depends on where the service boundary is considered to be since you are allowed only one OCPD for the fire pump, IIRC. Then it might be better to use an unfused disconnect instead of a breaker. The fire pump controller will have OCPD inside it anyway.