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Thread: Wire size reduction for branch circuits

  1. #1
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    Wire size reduction for branch circuits

    My company installed LED lights in a school. The branch circuit is a 20 amp breaker with 12-2 wire. We installed 40 watt LED panels and a ceiling sensor with 14-3 MC from the switch leg box. The inspector failed us do to the fact the breaker is 20 amp therefore all wire must be 12 gauge. The ceiling sensor only draws 3 amps and has 18 wire hooked up internally. I referenced 240.5 (B)(2) witch states 14 can be used as fixture wire on a 20 amp breaker, but also went to table 402.3 and THWN is no listed. Is there any other code I should reference?
    Thanks all

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    The reference is that the inspector is correct. The sensor is part of the branch circuit not part of the fixture wiring so it must be 12 awg, IMO @D_Norris
    Last edited by Dennis Alwon; 05-01-19 at 05:37 PM.
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    Quote Originally Posted by D_Norris View Post
    My company installed LED lights in a school. The branch circuit is a 20 amp breaker with 12-2 wire. We installed 40 watt LED panels and a ceiling sensor with 14-3 MC from the switch leg box. The inspector failed us do to the fact the breaker is 20 amp therefore all wire must be 12 gauge. The ceiling sensor only draws 3 amps and has 18 wire hooked up internally. I referenced 240.5 (B)(2) witch states 14 can be used as [Red]fixture wire on a 20 amp breaker, [Red]but also went to table 402.3 and THWN is no listed. Is there any other code I should reference?
    Thanks all
    Fixture Wire is the wire that is located on the inside of light fixtures. The Branch Circuit wiring is the wiring from the breaker to the outlet box.

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    I agree, the #14 conductors are part of the branch circuit and must be a minimum of 20 amps unless you want to install 15 amp circuit breakers.
    Rob

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    All responses based on the 2014 NEC unless otherwise noted

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    Quote Originally Posted by xformer View Post
    Fixture Wire is the wire that is located on the inside of light fixtures. The Branch Circuit wiring is the wiring from the breaker to the outlet box.
    But what is the wire in the whip of a troffer? I always thought that was "fixture wire", as I dont see how it could be so small if it isnt.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

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    Quote Originally Posted by electrofelon View Post
    But what is the wire in the whip of a troffer? I always thought that was "fixture wire", as I dont see how it could be so small if it isnt.

    That would be a fixture tap and fall under 402.5 and 240.5(B)(2).
    Rob

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    All responses based on the 2014 NEC unless otherwise noted

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    Quote Originally Posted by electrofelon View Post
    But what is the wire in the whip of a troffer? I always thought that was "fixture wire", as I dont see how it could be so small if it isnt.
    If it is part of the fixture and its listing it is not under the NEC.

    Roger
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    Wire from remote ballast can be #14, #16 depending on distance.
    It's considered part of the fixture. Or was code could have changed from the last time I did any work.

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    190506-2136 EDT

    Any wiring in series with branch circuit wiring that can carry total branch circuit current, in this case rated 20 A, must be able to handle that rated current.

    The wire in a load that only connects to a branch circuit only has to carry the current to that particular load. Somewhat the assumption is that the current in the load is only the current of that load, and over normal current is not expected in the individual load. Under some sort of shorting conditions the current in the individual load could be higher than its normal current and might overheat the insulation of the smaller wire. But this is tolerated by the way the code is written. Extension cords are an example of a possible problem, and overloaded extension cords have caused fires.

    To understand this problem you need to consider that many branch circuits have several parallel loads on the circuit. These loads are individually smaller than the circuit rating. Thus, current to an individual load is smaller than the total circuit load. But when you look at the total circuit, then the circuit current is the sum of all the individual loads.

    This is why you need to understand circuit theory and analysis.

    .

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    Just change the breaker to 15 amp.

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