fire pump

[dolphins]

The generator service the fire pump only required to size at its full load. Anyone can interpret that we do not need to size the fire pump overcurrent device at the emergency service connection at lock rotor current. The 1999 code does seem to say that the ocd at the emergency service still need to be sized at the lock rotor current. Why do we have to size at 6 times when the load of the emergency generator can only take max. @ 125%?

 

[rick5280]

Re: fire pump

I'm not to familiar with this type of setup, but one thought I had was that the generator may be sized to handle more than just the fire pump system. If it is, then even 125% of the generator output could be in excess of the LRC of the fire pump.

In looking at the NEC 2002 Handbook (Article 695.3), there is some commentary after this article which reads "Where the alternative source of power is an on-site generator, the alternative source disconnecting means and the alternative source overcurrent protective device(s) for the electric-drive fire pump are not required to be sized for locked-rotor current of the fire pump motor(s). Rather, the circuit components of the alternative source are permitted to be sized according to Article 430, provided they are ?selected or set to allow instantaneous pickup and running of the fire pump load.? See 445.12(A). ?"

Rick

 

[hbendillo]

Re: fire pump

I am a little confused about what you are saying. The feeder from an onsite generator to the fire pump only has to be sized as we would a normal motor circuit not locked rotor amps. The circuit from the primary source, usually the service for the building has to be sized at locked rotor. Also, an emergency generator will not run very long at 125% of its rated load.

 

[bob]

Re: fire pump

Take a look at 695.3A it says "Where reliable and
CAPABLE of carrying the lock rotor amps ....."
Then look at 695.3B1 Generator Capacity.
The generator should have capacity to carry the starting and running or the motor and other load.
If the alternate source is a generator then you do not need the overcurrent device to be 6 time the FLA of the motor. However, if you are sizing
the generator at only 125% of the FLA, I doubt that it will allow starting. You might want to chjeck this out. The circuit components are to be sized according to Article 430.
Good question.

[ April 17, 2003, 12:02 AM: Message edited by: bob ]