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Thread: Fire Pump Service & Utility Company Responsibilities?

  1. #1
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    Fire Pump Service & Utility Company Responsibilities?

    Does the NEC's requirement for sizing overcurrent protection for fire pumps to accommodate the locked rotor ampacity of the motor apply to up-stream primary overcurrent protection (utility company's equipment), or does the NEC only cover overcurrent devices within or ahead of the fire pump controller (building equipment)?

    What I've got is a 200 HP 480V 3PH Electric Fire Pump with a dedicated utility pad mount transformer. The utility company wants to provide a 300 kVA transformer at 19.9 KV 3PH primary and 8 Amp primary fuses.

    The 200 HP fire pump LRA per NEC 430.251(B) is 1450 Amps at 480V 3PH. This locked rotor information for the motor would equate to about 1205 kVA and 35 Amps at 19.9 kV 3PH.

    Now, the NEC does not require conductors to be sized by the LRA nor does it require transformers to be sized for the LRA. But in order to meet NFPA 20 and be a "reliable service", wouldn't the utility company's transformer and primary fuses need to accommodate the LRA? The utility is saying they want to size the transformer for the 200 HP load and then protect their transformer, hence the 8 Amp fuses. This would not carry the LRA indefinitely as is required by the NEC. But does the NEC get to determine what the utility company does?

    Thoughts? Thanks!

  2. #2
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    Welcome to the forum.

    The NEC does not cover power company equipment. Basically the NEC starts where the power company ends and that is called the Service Point.
    Once in a while you get shown the light
    In the strangest of places if you look at it right. Robert Hunter

  3. #3
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    Agreed. I know they're not governed by the same set of rules as the rest of us. And they're really good at making that evident too! I guess the question then diverts to NFPA 20's definition of a reliable service (and AHJ's interpretation) rather than the NEC.

    NEC wants our fire pump to be connected to a reliable source and for our installation to be designed to allow operation at the LRA indefinitely (until equipment is destroyed). The utility company's source meets all conditions in NFPA 20 as far as reliable source is concerned. However, the utility company's equipment would not facilitate such operation at the LRA for more than a few cycles (inrush). Could the utility's service then not be considered "reliable" in the eyes of the NEC based on the fact that it won't allow indefinite operation at the LRA of the motor as NEC requires?

    Maybe this is where "under proper engineering supervision" and the AHJ's decision comes into play.

  4. #4
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    Quote Originally Posted by VBE View Post
    Agreed. I know they're not governed by the same set of rules as the rest of us. And they're really good at making that evident too! I guess the question then diverts to NFPA 20's definition of a reliable service (and AHJ's interpretation) rather than the NEC.

    NEC wants our fire pump to be connected to a reliable source and for our installation to be designed to allow operation at the LRA indefinitely (until equipment is destroyed). The utility company's source meets all conditions in NFPA 20 as far as reliable source is concerned. However, the utility company's equipment would not facilitate such operation at the LRA for more than a few cycles (inrush). Could the utility's service then not be considered "reliable" in the eyes of the NEC based on the fact that it won't allow indefinite operation at the LRA of the motor as NEC requires?

    Maybe this is where "under proper engineering supervision" and the AHJ's decision comes into play.
    I'm going to suggest the source is not "reliable" since 695.3(A) specifically says:

    (A) Individual Sources. Where reliable, and where ca-
    pable of carrying indefinitely the sum of the locked-rotor
    current
    of the fire pump motor(s) and the pressure mainten-
    ance pump motor(s) and the full-load current of the asso-
    ciated fire pump accessory equipment when connected to
    this power supply, the power source for an electric motor
    driven fire pump shall be one or more of the following.

    (1) Electric Utility Service Connection...etc

  5. #5
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    Client Coverage

    What I've done in the past is perform a voltage-drop calculation that determines the minimum size transformer based on starting and running VD per NEC 695. Then publish those findings to the Utility and the client. I would also plot the Utility's ocpd against the motor locked rotor amperage for determination of appropriate fusing.
    I think the client is covered because they've done their due-diligence and they only have control of the secondary devices.

  6. #6
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    Quote Originally Posted by mayanees View Post
    What I've done in the past is perform a voltage-drop calculation that determines the minimum size transformer based on starting and running VD per NEC 695. Then publish those findings to the Utility and the client. I would also plot the Utility's ocpd against the motor locked rotor amperage for determination of appropriate fusing.
    I think the client is covered because they've done their due-diligence and they only have control of the secondary devices.
    They may have control of only the secondary devices, but the AHJ is well within his/her rights to consider the fusing on the primary side in evaluating the reliability of the source. It puts the client in a tough spot if the utility won't budge. I would guess it gets passed on to the Board of Public Utilities or equivalent in that case.

  7. #7
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    Quote Originally Posted by gadfly56 View Post
    I'm going to suggest the source is not "reliable" since 695.3(A) specifically says:

    (A) Individual Sources. Where reliable, and where ca-
    pable of carrying indefinitely the sum of the locked-rotor
    current
    of the fire pump motor(s) and the pressure mainten-
    ance pump motor(s) and the full-load current of the asso-
    ciated fire pump accessory equipment when connected to
    this power supply, the power source for an electric motor
    driven fire pump shall be one or more of the following.

    (1) Electric Utility Service Connection...etc
    That's an interesting point, and I would say you are probably right.

    Quote Originally Posted by mayanees View Post
    What I've done in the past is perform a voltage-drop calculation that determines the minimum size transformer based on starting and running VD per NEC 695. Then publish those findings to the Utility and the client. I would also plot the Utility's ocpd against the motor locked rotor amperage for determination of appropriate fusing.
    I think the client is covered because they've done their due-diligence and they only have control of the secondary devices.
    True, they don't have control of the utility, but they do have the option of installing a alternate source. In this case, I would say the alternate source is required, unless the utility will increase the delivery capacity. That alternate source could either be a generator, or even a diesel motor pump.

    It's apparently been a while since I've designed electrical for a fire pump. The NEC 2011 handbook has some commentary I've never read before on some exact requirements for a "reliable source". It's extracted from NFPA 20.

    Overhead lines are not allowed since the fire dept. might have to cut them for firefighting. And any outages caused by other than natural disasters or grid management failure (i.e. regional blackouts) cause the utility to be considered unreliable.

  8. #8
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    Quote Originally Posted by steve66 View Post
    That's an interesting point, and I would say you are probably right.



    True, they don't have control of the utility, but they do have the option of installing a alternate source. In this case, I would say the alternate source is required, unless the utility will increase the delivery capacity. That alternate source could either be a generator, or even a diesel motor pump.

    It's apparently been a while since I've designed electrical for a fire pump. The NEC 2011 handbook has some commentary I've never read before on some exact requirements for a "reliable source". It's extracted from NFPA 20.

    Overhead lines are not allowed since the fire dept. might have to cut them for firefighting. And any outages caused by other than natural disasters or grid management failure (i.e. regional blackouts) cause the utility to be considered unreliable.
    Just to be clear, the prohibition on overhead lines is only on the user premises, not on the POCO right-of-way outside the property.

  9. #9
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    Quote Originally Posted by gadfly56 View Post
    Just to be clear, the prohibition on overhead lines is only on the user premises, not on the POCO right-of-way outside the property.
    Yes, I was trying to summarize, assuming the OP would refer to the full text in the handbook or even NFPA 20.

    Chances are, if you trace the supply back far enough, you are going to find some overhead lines somewhere

  10. #10
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    Quote Originally Posted by steve66 View Post
    Yes, I was trying to summarize, assuming the OP would refer to the full text in the handbook or even NFPA 20.

    Chances are, if you trace the supply back far enough, you are going to find some overhead lines somewhere
    In NJ that would be nearly everywhere.

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