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Thread: Fire Pump OCPD

  1. #1
    Join Date
    Mar 2003
    Location
    Missouri
    Posts
    54

    Fire Pump OCPD

    My understanding of sizing the OCPD for fire pump is to use the lock rotor current (if we used an overcurrent at the normal source). But my boss told that I need to use 125% of FLA when we size it from an emergency source (Generator). Not sure why, any thoughts???

  2. #2
    Join Date
    Feb 2003
    Location
    Indianapolis
    Posts
    6,102

    Re: Fire Pump OCPD

    The following two sections deal with overcurrent and overload protection. I do not see how the feeder from a generator is any different from the service from an electric utility.

    695.4(1) Overcurrent Device Selection The overcurrent protective device(s) shall be selected or set to carry indefinitely the sum of the locked-rotor current of the fire pump motor(s) and the pressure maintenance pump motor(s) and the full-load current of the associated fire pump accessory equipment when connected to this power supply. The requirement to carry the locked-rotor currents indefinitely shall not apply to conductors or devices other than overcurrent devices in the fire pump motor circuit(s).

    695.6(D) Overload Protection Power circuits shall not have automatic protection against overloads. Branch-circuit and feeder conductors shall be protected against short circuit only. Where a tap is made to supply a fire pump, the wiring shall be treated as service conductors in accordance with 230.6. The applicable distance and size restrictions in 240.21 shall not apply.

    Exception No. 1: Conductors between storage batteries and the engine shall not require overcurrent protection or disconnecting means.

    Exception No. 2: For on-site standby generator(s) rated to produce continuous current in excess of 225 percent of the full-load amperes of the fire pump motor, the conductors between the on-site generator(s) and the combination fire pump transfer switch controller or separately mounted transfer switch shall be installed in accordance with 695.6(B) or protected in accordance with 430.52.

    The protection provided shall be in accordance with the short-circuit current rating of the combination fire pump transfer switch controller or separately mounted transfer switch.
    Charlie Eldridge, Indianapolis, Utility Power Guy
    Responses based on the 2011 NEC, unless stated otherwise.

  3. #3
    Join Date
    Mar 2003
    Location
    Missouri
    Posts
    54

    Re: Fire Pump OCPD

    Charlie, look at the NEC 2005 Handbook page 1043 sec. 695.3(B)(1) explanation. It states, if we have an on site generator, the overcurrent device for the fire pump are not required to be sized for the locked-rotor current and it is permitted to size it per article 430. Am I missing something?? Thank you.

  4. #4
    Join Date
    Feb 2003
    Location
    Indianapolis
    Posts
    6,102

    Re: Fire Pump OCPD

    The text you are referring to is:

    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 "allow instantaneous pickup of the full [fire] pump room load," as specified by 9.6.5 in NFPA 20. See 445.12(A).

    I am not familiar with NFPA 20 so someone else will have to help here. Sorry.
    Charlie Eldridge, Indianapolis, Utility Power Guy
    Responses based on the 2011 NEC, unless stated otherwise.

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