electric supply to fire pump 2

[jacphi]

i have a controlgear rated for 1200A,480v. one of the feeder is a fire water pump.having a FLA of 240A(locked rotor current 1500A Approx. i am extracting the local std requirement for fire pump unit package.
"QUOTE"
The protection schemes for Fire Pump Unit (FPU) packages shall comply with NFPA 20 and NFPA 70. In general, these standards require that the motor be allowed to operate under locked rotor condition continuously and is only automatically disconnected under short-circuit conditions.
Exception :
The exception to these requirements is that where a FPU package is fed from a bus that has ground overcurrent protection on the incomers or supply transformers, the feeder to the FPU package shall have ground overcurrent protection, and all other feeders connected to the same buses or transformers shall have ground overcurrent protection.
"UNQUOTE"

my question is will this controlgear be sufficient to supply the locked rotor condition mentioned? does the exception above mean that by providing groung fault protection i do not have to comply with require that the motor be allowed to operate under locked rotor condition continuously. please comment.

 

[dpc]

You need to review the National Electrical Code (NFPA 70)Article 695. If I understand your switchgear arrangement, the fire pump motor is supplied from a feeder on the switchgear bus. In general, NEC requires that the fire pump be supplied ahead of any other loads, on a separate supply connected directly to the service. It must connected ahead of the service disconnecting means. It is likely that your arrangement would not meet this requirement.

As for the overcurrent protection, if the fire pump is fed ahead of the switchgear, as it should be, the rating of switchgear is not really a concern.

The fire pump supply must be capable of providing locked-rotor current indefinitely, regardless of any ground fault protection per Article 695. I'm not aware of any exceptions to this in the NEC.

 

[jacphi]

thanks for the reply in fact the fire water pump is fed by a 480v motor control centre. the motor control centre is being fed from the 480v switchgear. i would also like to know if the The fire pump supply must be capable of providing locked-rotor current indefinitely i.e 1500A. should the Motor control centre also be rated for 1500A.

 

[dpc]

If you are outside the US, my previous response (and the rest of this response) should be ignored. It applies only to US installations covered by NFPA.

If you are in the US, the installation you are describing is **illegal** for the reasons given in my first reply.

From purely a technical basis, the continuous current rating of the MCC bus is not really a factor, since the locked rotor current will stop once the fire pump motor either accelerates or burns up. The real issue is making sure that the circuit breakers do not trip for a locked rotor condition. You do need to verify that the upstream transformer is capable of starting the motor - this will require a motor starting analysis to determine voltage drop during starting.

Also, the fire pump motor must be controlled by a UL-labled Fire Pump Controller. You can not use an MCC starter. But this is really a moot point, since the fire pump cannot be legally fed from an MCC.

 

[jacphi]

From purely a technical basis, the continuous current rating of the MCC bus is not really a factor, since the locked rotor current will stop once the fire pump motor either accelerates or burns up.
for the above said comment wouldnt it be better if the mcc bus is capable of withstanding the locked rotor current.

 

[rbulsara]

I think you are misinterpreting.

Ground fault is a form of short circuit. Only difference being GF pick up could be set less than LRA.

You still need the motor branch breaker to carry LRA indefinitely.

If the 1200A board has a main rated 1600A ,local or remote AND is dedicated for the fire pump only then it meets the code.

If you are feeding other loads too, you have to feed the 1200A board with a larger than 1600A feeder (conductors) and protect with appropriate breaker, to meet the total demand of LRA of the fire pump and other continuous loads, more over you need a separate 1600A breaker in the 1200A board! This becomes a far less than a professional set up.

(hint: tap rules apply to a 1200A rated board fed with a 1600A or larger breaker)

The 1200A bus rating is not the issue as it meets the conductor rating for a fire pump, but there are other code issues related to breaker sizing.

 

[WhoJuntao]

@dpc:

All - except: common wealth, china and ex-urss countries have in their ~local codes~:

"Unless otherwise specified by NFPA".

On one project:
>homer: we put *blah* in the sepcs according to the NFPA
>client: we know the NFPA , we want to know what You think
>homer: doesn't matter, if it's not as per NFPA your system won't get approval from the local authorities
>client: but we are the local authorities! so why don't we forget your "specs" and just put one line: see NFPA
>homer: you might be joking, but i think that's a very good idea, are you serious about it?
>client: you're da.. right, that's a whole load off. Agreed.

and you say Forget it if you're out of the states? man get out of the states for a while and see for yourself