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Thread: Mismatched wire gauges in a 240 volt, one phase street lighting system

  1. #1
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    Mismatched wire gauges in a 240 volt, one phase street lighting system

    An inspector on a state highway project noticed that for a 240 volt street lighting system, the contractor has installed 1#6 and 1#8 conductors instead of the 2#8 called out in the plans. I know this is not standard practice for the conductors to be of different gauges but does the NEC specifically prohibit doing this? And what problems might this cause if any. The lighting system has LED luminaires.

  2. #2
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    No code issue or operational problems from on conductor being larger than what the circuit requires.
    Don, Illinois
    Ego is the anesthesia that deadens the pain of stupidity. Dr. Rick Rigsby
    (All code citations are 2017 unless otherwise noted)

  3. #3
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    The NEC doesn't care if the condcutors are different sizes. You would need to ask for a code reference to try and figure what he was thinking.
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

  4. #4
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    Mixing the sizes is no biggie.

    One problem that can arise is the size of an EGC when upsizing circuit conductors, 250.122(B).

    Is there an EGC?
    "Electricity is really just organized lightning." George Carlin


    Derek

  5. #5
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    Yes, there is an ECG. State Specs and NEC says it should match the size of the largest ungrounded conductor and hopefully this is what the contractor did.\
    Thanks.

  6. #6
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    120/240V or 240/480V single phase

    Is this for a 120/240V single phase or 240/480V single phase lighting system and are you connecting them 240 L-L or 240L-N? We used 240/480V single phase for street lighting projects in our area which is why I'm asking. I can't site a code source at this time, but if it is 120-240V and you have it connected L-L, I would think there would be a code requirement for same sized conductors, but I cannot cite it at this time.

  7. #7
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    Quote Originally Posted by tw1156 View Post
    Is this for a 120/240V single phase or 240/480V single phase lighting system and are you connecting them 240 L-L or 240L-N? We used 240/480V single phase for street lighting projects in our area which is why I'm asking. I can't site a code source at this time, but if it is 120-240V and you have it connected L-L, I would think there would be a code requirement for same sized conductors, but I cannot cite it at this time.
    no, requirement to match sizes. Conductors just have to have correct ampacity.
    "Electricity is really just organized lightning." George Carlin


    Derek

  8. #8
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    Possibly done to lower voltage drop enough to meet a goal, and only one conductor needed to be bigger to do so.

    Or he ran out of #8 and installed #6 instead of buying more.

    Nothing against Code to have half of an upgrade unless it adversely affects conduit fill, and is otherwise done properly.

    As mentioned, there is a Code that requires the EGC to be sized accordingly...

  9. #9
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    See #4
    4 answers to an electrical question
    1. Code answer
    2. AHJ answer
    3. Toms answer
    4. Truck answer
    Moderator-Washington State
    Ancora Imparo

  10. #10
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    You could run one conductor copper and the other aluminum if you wanted as long as minimum ampacity requirements are met and overcurrent protection rules are met.

    You can't mismatch conductors that are in parallel to one another for the purpose of making an overall higher current carrying capacity conductor.

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