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Thread: Voltage Drop

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    Voltage Drop

    I am running a 120v/20a circuit 500ft for a gate operator. Using copper and a 3.6volt loss in the Vd calculation I get a wire size of #1awg. The ground would calculate to the same using 250.122(B). Is this correct? It sure does not seem so!!

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    The resistance of copper wire at 20 deg C is about 14% less than at 60 deg C. I assume in your application the conductors would be running closer to 20 than 60 deg C? If so, that would probably be enough to let you use #2s and still meet your spec. (but admittedly still a lot of copper to buy for a 20A circuit). I would expect a significant reduction in temperature rise from self heating with #2s vs. #12s for example, because of the roughly 1/10th power dissipation per foot (at a given current) and the larger surface area of the wires. That is, unless you're planning to run it with other circuits that significantly increase the temperature of the conductors.

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    Quote Originally Posted by Informed View Post
    I am running a 120v/20a circuit 500ft for a gate operator. Using copper and a 3.6volt loss in the Vd calculation I get a wire size of #1awg. The ground would calculate to the same using 250.122(B). Is this correct? It sure does not seem so!!
    Yes! On 15, 20 and 30 amp circuits since the equipment ground is the same size as the power conductors when you increase the power conductors the equipment ground would be equal size.
    At my age, I'm accustomed to restaurants asking me to pay in advance, but now my bank has started sending me their calendar one month at a time.

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    Quote Originally Posted by synchro View Post
    The resistance of copper wire at 20 deg C is about 14% less than at 60 deg C. I assume in your application the conductors would be running closer to 20 than 60 deg C? If so, that would probably be enough to let you use #2s and still meet your spec. (but admittedly still a lot of copper to buy for a 20A circuit). I would expect a significant reduction in temperature rise from self heating with #2s vs. #12s for example, because of the roughly 1/10th power dissipation per foot (at a given current) and the larger surface area of the wires. That is, unless you're planning to run it with other circuits that significantly increase the temperature of the conductors.
    Good grief, Charlie brown
    At my age, I'm accustomed to restaurants asking me to pay in advance, but now my bank has started sending me their calendar one month at a time.

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    If the opener has a battery, the power merely recharges it, so you can practically ignore the voltage drop; maybe use #10.

    Disclaimer: this opinion is only my own, so take it with the appropriate amount of wariness.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

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    If you have 240V available, another alternative would be to run #10s and take about a 5% voltage drop to 228V. Then use a transformer with a 228V input tap and a 120V output:


    https://www.galco.com/buy/Jefferson-...?scrollTo=docs

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    Quote Originally Posted by Informed View Post
    I am running a 120v/20a circuit 500ft for a gate operator. Using copper and a 3.6volt loss in the Vd calculation I get a wire size of #1awg. The ground would calculate to the same using 250.122(B). Is this correct? It sure does not seem so!!
    Your gate opener is likely only 2 or 3 amps.
    For most economical, install 14 AWG 15 A circuit with a small UPS with small battery at the gate.

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    Quote Originally Posted by Informed View Post
    I am running a 120v/20a circuit 500ft for a gate operator. Using copper and a 3.6volt loss in the Vd calculation I get a wire size of #1awg. The ground would calculate to the same using 250.122(B). Is this correct? It sure does not seem so!!
    What is the actual load?
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

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    I just ran a 120V circuit out to a scoreboard 300 Ft. current drawn is 3.5 amps total. Using #10 I have a 1.85 voltage drop.

    Works fine. You should be ok with #10 if amperage is low.

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    Quote Originally Posted by infinity View Post
    What is the actual load?
    Good question. I'm with Junkhound on this. I can't see a gate opener taking anything like 30A.

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