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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!!

    #2
    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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      #3
      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.

      Comment


        #4
        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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          #5
          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.
          Master Electrician
          Electrical Contractor
          Richmond, VA

          Comment


            #6
            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

            Comment


              #7
              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.

              Comment


                #8
                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 2017 NEC unless otherwise noted

                Comment


                  #9
                  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.

                  Comment


                    #10
                    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.

                    Comment


                      #11
                      Originally posted by kec View Post

                      Works fine. You should be ok with #10 if amperage is low.
                      Ya know, #10 is what I was thinking. I would probably use that without even thinking Much about it.
                      Ethan Brush - East West Electric. NY, WA. MA

                      "You can't generalize"

                      Comment


                        #12
                        Originally posted by synchro View Post
                        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
                        228 is voltage with a load, if you then make an input to a 228 v tap, you get what you want when loaded, but have overvoltage when not loaded.



                        If only a 3.6% VD for a gate motor - I'd probably do nothing for VD. Not a continuous enough load to have much concern about. If at a dwelling, maybe even less use of this motor. It only operates for 10-20 seconds to open, then another 10-20 to close and may sit there for hours before called upon again, it can probably handle the little bit of increased current because of VD if this is all the use it will normally see and has plenty of time to cool down before needed again.
                        I live for today, I'm just a day behind.

                        Comment


                          #13
                          This and I assume most gate opener manufacturers provide specific guidelines for the wire size to be used for a given wire length:

                          https://www.google.com/url?sa=t&sour...zJ2jV3#page=16

                          They also mention an optional heater (presumably for northern climates) which would add an additional load.

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