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Thread: Branch Circuit with motor and non-motor load

  1. #1
    Join Date
    Feb 2015
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    Western PA
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    Branch Circuit with motor and non-motor load

    This is for a project in Ohio, 2017 NEC.

    Customer is adding a wash-water holding tank out back of their production facility. The water will be pumped into a tanker truck using a sump pump controlled by a manual motor starter (with overload protection) located at the tank (outdoors). Panel in the building is 208Y/120 3 phase.

    At the tank I want to power a 5 HP 3 phase pump (FLC = 16.7A) and a 1A light. Let's assume that the light is a continuous load. By 430.53(B) "If Smallest Rated Motor Protected" I can size the breaker (in the building) at 16.7 * 2.5 = 41.75, next size up is 45A breaker.

    To size the conductors, I use 430.24 "Several Motors or a Motor(s) and Other Load(s)" and calculate 16.7 * 1.25 + 1 * 1.25 = 22.125 A. In the conductor table in section 310, #12 Cu THWN is rated for 25 A in the 75°C column. However, because I am powering a non motor load, does 240.4(D) limit me to a 20 A breaker if I use #12 Cu to supply the light? In that case, I could opt for #10 Cu and a 30 A breaker, or if I went to #8 Cu, I would then be free to use the 45 A breaker?

  2. #2
    Join Date
    Dec 2007
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    NE Nebraska
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    37,504
    Tricky one since certain types of lights can go on a 50 amp circuit with tap conductors to individual luminaires. If you don't have a light with heavy duty lampholders the chances of even considering it get less though.
    I live for today, I'm just a day behind.

  3. #3
    Join Date
    Feb 2015
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    Western PA
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    Quote Originally Posted by kwired View Post
    Tricky one since certain types of lights can go on a 50 amp circuit with tap conductors to individual luminaires. If you don't have a light with heavy duty lampholders the chances of even considering it get less though.
    Thanks for this tip, I didn't consider Table 210.24 which requires the heavy duty lampholders.

    To clarify my original post, the light fixture is 120V single phase. Therefore the ampacity calculation was not quite right since I was mixing three phase with single phase, but it was conservative.

    I will probably go with a separate 120V circuit for the light, since it's only one extra wire (the neutral is not needed for the motor).

    The question still stands as to assuming that I have a heavy duty lampholder, do I have to follow the conductor sizing in Table 210.24 (#12 with 20A breaker, #10 with 30A breaker, etc.), or can I use the smaller conductors apparently allowed by 430.24?

  4. #4
    Join Date
    Jun 2017
    Location
    WI, USA
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    363
    Power the light with a separate branch circuit and call it a day.

  5. #5
    Join Date
    Jan 2007
    Posts
    3,552
    Since it's being controlled by a Manual Motor Starter at the pump location, If it were me, I'd install a 60 amp 4w feeder out to that location, install a 3ph subpanel with a 3p breaker to feed the pump and a 1p 20 to feed the light with some space in case a service receptacle may need to be added in the future.

    You'll never regret installing that distribution out there.

    JAP>

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