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    Parking lot, site lighting voltage drop requirement

    Do we need to limit 3% voltage drop for exterior parking lot and site lighting even if they are LED lights?
    Is this a code requirement? This will make a huge cost difference.

    #2
    Pretty sure that voltage drop limitations are recommendations only, and are there to help ensure loads are operating efficiently and won't die prematurely, but it isn't considered a safety issue. Also, do you have a fairly even/symmetrical lot lighting layout so you can use center of load to calculate voltage drop, instead of calculating voltage drop to the furthest fixtures?
    I'm offended.

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      #3
      More info helps, also. For example, some LED fixtures might be already specified for a wide voltage range. There are also other ways to mitigate voltage drop without upsizing the conductors, assuming this is your concern.

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        #4
        Originally posted by Kansas Mountain View Post
        Pretty sure that voltage drop limitations are recommendations only, and are there to help ensure loads are operating efficiently and won't die prematurely, but it isn't considered a safety issue. Also, do you have a fairly even/symmetrical lot lighting layout so you can use center of load to calculate voltage drop, instead of calculating voltage drop to the furthest fixtures?
        How do you do a center of load to voltage drop calculation?

        Sent from my Pixel 2 XL using Tapatalk

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          #5
          Originally posted by cburke1111 View Post
          How do you do a center of load to voltage drop calculation?

          Sent from my Pixel 2 XL using Tapatalk
          If you have multiple EQUAL loads, that are placed EQUALLY along the length of the circuit, find the center of the circuit based on the actual installation path that will be used. Calculate voltage drop to that point, instead of the furthest load. This takes advantage of the fact that the loads closer to the panel will have less voltage drop. That was explained to me by a really good electrical PE a few years ago when doing designs for big-box retail store parking lot lighting.
          I'm offended.

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            #6
            Originally posted by Kansas Mountain View Post
            If you have multiple EQUAL loads, that are placed EQUALLY along the length of the circuit, find the center of the circuit based on the actual installation path that will be used. Calculate voltage drop to that point, instead of the furthest load. This takes advantage of the fact that the loads closer to the panel will have less voltage drop. That was explained to me by a really good electrical PE a few years ago when doing designs for big-box retail store parking lot lighting.
            Thank you

            Sent from my Pixel 2 XL using Tapatalk

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              #7
              Originally posted by cburke1111 View Post
              How do you do a center of load to voltage drop calculation?

              Sent from my Pixel 2 XL using Tapatalk
              I think there's a formula in the American Electrician's Handbook that even allows for un-evenly spaced loads.

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                #8
                Originally posted by MAC702 View Post
                More info helps, also. For example, some LED fixtures might be already specified for a wide voltage range. There are also other ways to mitigate voltage drop without upsizing the conductors, assuming this is your concern.
                yeah. some led drivers are 120~277 off of one tap.

                they are gonna consume the wattage they are rated for,
                irregardless of the voltage. if the voltage is low, and you
                consume the same power, current will go up. if it goes over
                the breaker rating, you will save a lot of power, at the expense
                of illumination.

                look at your driver cut sheets.
                ~New signature under construction.~
                ~~~~Please excuse the mess.~~~~

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                  #9
                  Originally posted by MAC702 View Post
                  More info helps, also. For example, some LED fixtures might be already specified for a wide voltage range. There are also other ways to mitigate voltage drop without upsizing the conductors, assuming this is your concern.
                  Yes

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                    #10
                    Originally posted by Fulthrotl View Post
                    yeah. some led drivers are 120~277 off of one tap.

                    they are gonna consume the wattage they are rated for,
                    irregardless of the voltage. if the voltage is low, and you
                    consume the same power, current will go up. if it goes over
                    the breaker rating, you will save a lot of power, at the expense
                    of illumination.

                    look at your driver cut sheets.
                    Are you talking about constant current drivers?

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                      #11
                      Originally posted by anbm View Post
                      Are you talking about constant current drivers?
                      i'm talking about a 27 watt driver, with an input voltage of 120~277, for example.

                      it's gonna pull 27 watts with a power source between those voltages.
                      it's gonna take more current with less voltage to get 27 watts.
                      ~New signature under construction.~
                      ~~~~Please excuse the mess.~~~~

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                        #12
                        Originally posted by anbm View Post
                        Do we need to limit 3% voltage drop for exterior parking lot and site lighting even if they are LED lights?
                        Is this a code requirement? This will make a huge cost difference.
                        Unless you have an energy code or other NEC amendments to comply with, the 3% that is mentioned in NEC is in an informational note and is just that - information (suggestive information in this case).

                        Originally posted by Fulthrotl View Post
                        i'm talking about a 27 watt driver, with an input voltage of 120~277, for example.

                        it's gonna pull 27 watts with a power source between those voltages.
                        it's gonna take more current with less voltage to get 27 watts.
                        More current means more voltage drop which makes current go up even further - until there is a balance. Also means more line losses.
                        I live for today, I'm just a day behind.

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