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Can I install a 120 volt receptical at my solar system racking?

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  • Can I install a 120 volt receptical at my solar system racking?

    This is probably a strange question best suited for the NEC experts.. I looked everywhere and couldn't find any information on it..

    I'm installing a 7.6kw grid tied (ground mount) solar system in my back yard.. The location just happens to be next to a high traffic area where we park the tractor, mower, etc and I would like to install a 120 volt outlet on the racking structure so I can plug in work tools, a battery charger when the mower battery dies, etc.

    My system requires a 120 foot cable run from my breaker box to the SMA inverter. While I could have gotten away with 6ga wires, I found some direct burial 4ga / 3 wire w/ground copper cable for scrap prices.

    Anyhow, since the 4ga cable is far too large to run directly into the SMA inverter's 3/4 conduit openings, I have to install a 12x12 inch square PVC junction box.. I will put a 3 pole distribution block into the box so I'll have both phases and a neutral available.

    I would like to tap off that distribution block and install a normal 120 volt household outlet at the same location. In fact, if its allowed, I might even install a 220 volt outlet for my welder.

    Is there anything that prevents this? From an electrical standpoint, I can't see there would be any issues but I'm wondering if there is some NEC code that prevents it.

    Thanks!

  • #2
    You can't just add an outlet, but what you could do is add a small sub panel to the area. The sub panel would be back fed from the array, and then the main feed would be the backfeed breaker you have in the main panel. Then you could put a few other circuits within the sub panel.

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    • #3
      First off you will need some type of over current protection (fuse or circuit breaker) to protect a receptacle or something like a remote power cb panel feeding the receptacle.

      I do not believe you are allowed to use split the output of a solar inverter going to your house panel and to a separate power panel although you can confirm that by talking to your local AHJ to find out.

      Each locality must meet some version of the NEC but also have their own rules which may or may not be more rigid then the latest NEC.

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      • #4
        Originally posted by Murby View Post
        since the 4ga cable is far too large to run directly into the SMA inverter's 3/4 conduit
        openings, I have to install a 12x12 inch square PVC junction box.
        I doubt anyone would fault you for taking a metal punch and putting the hole size you need at
        the position you need it, as happens here. Bruce Roe

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        • #5
          Originally posted by bcroe View Post

          I doubt anyone would fault you for taking a metal punch and putting the hole size you need at
          the position you need it, as happens here. Bruce Roe
          He is probably referring to the wire termination on the inverter not being big enough to accept that #4 wire.

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          • #6
            Absolutely you can. It just needs to be code compliant. Run a 3-wire circuit from your main beaker panel through a fuse. Or better yet find a circuit on your homes exterior walls and tap it. Any home built recently will have one dedicated circuit by the Air Conditioning compressor, Just tap it and be sure to use a GFCI recept.
            MSEE, PE

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            • #7
              Originally posted by Sunking View Post
              Absolutely you can. It just needs to be code compliant. Run a 3-wire circuit from your main beaker panel through a fuse. Or better yet find a circuit on your homes exterior walls and tap it. Any home built recently will have one dedicated circuit by the Air Conditioning compressor, Just tap it and be sure to use a GFCI recept.
              I believe the OP just wanted to tap the output of the inverter at the inverter for that receptacle.

              Can you basically wire the output of the inverter to the house panel as well as to a dedicated receptacle that is protected with an OC device?

              I wasn't sure but even if it is ok per the NEC is might not be ok with the AHJ.

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              • #8
                Is the inverter outside, at the array ?
                Anyway, you can't mix DC and AC wires in the same conduit.
                But you can run a feed from your main panel to the yard.
                Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                solar: http://tinyurl.com/LMR-Solar
                gen: http://tinyurl.com/LMR-Lister

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                • #9
                  The inverter is outdoors.

                  I've decided to do away with the junction box and distribution block and just install an 8 place sub-panel.. Its actually cheaper than having to purchase the box and distribution block and all the other garbage.

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                  • #10
                    Originally posted by Murby View Post
                    The inverter is outdoors.

                    I've decided to do away with the junction box and distribution block and just install an 8 place sub-panel.. Its actually cheaper than having to purchase the box and distribution block and all the other garbage.
                    Ok. To be clear you are installing a remote power panel that is connected to your main house panel. At the remote panel you are backfeeding the output of the solar inverter as well as feeding an outdoor receptacle.

                    Just make sure you follow the code when you size your remote panel including the breaker feeding it and the cable from the main panel.

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                    • #11
                      Originally posted by SunEagle View Post

                      Ok. To be clear you are installing a remote power panel that is connected to your main house panel. At the remote panel you are backfeeding the output of the solar inverter as well as feeding an outdoor receptacle.

                      Just make sure you follow the code when you size your remote panel including the breaker feeding it and the cable from the main panel.
                      My plan is to install an 8 place (16 circuit) 125amp sub panel with main lugs (NOT Main Breaker). It will be fed by a 4ga/3wire +grnd direct burial cable. The breaker in my home will be 70 amps and the 4ga will feed directly to the lugs with an isolated neutral wire. From there, I will install a 30 amp (2pole) breaker to the inverter, then single pole 15 amp (GFCI) breaker to an outlet and a 10amp breaker to a auxiliary yard light.

                      I will be sure that the inverter feeds the sub panel at the opposite end of buss bar from the main lugs. The inverter is 6kw.

                      Does that sound like a good plan?

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                      • #12
                        Originally posted by Murby View Post

                        My plan is to install an 8 place (16 circuit) 125amp sub panel with main lugs (NOT Main Breaker). It will be fed by a 4ga/3wire +grnd direct burial cable. The breaker in my home will be 70 amps and the 4ga will feed directly to the lugs with an isolated neutral wire. From there, I will install a 30 amp (2pole) breaker to the inverter, then single pole 15 amp (GFCI) breaker to an outlet and a 10amp breaker to a auxiliary yard light.

                        I will be sure that the inverter feeds the sub panel at the opposite end of buss bar from the main lugs. The inverter is 6kw.

                        Does that sound like a good plan?
                        I assume that both the 70A will be at the opposite end of feeder for it's busbar, as well as the 30A will be at the far end from the lugs on it's busbar

                        I *think* there's some weirdness in one of the versions of NEC that it could be interpreted that you need to use the 70A in your 120% rule calculations on the main panel.
                        1> figure out which version of NEC you're on.
                        2> draw up your plans exactly as they'll be installed and talk to the plan inspector to make sure what you're planning is fine. (logically it's obvious you'd only have 30A backfeed at the main panel. But I could see a plan inspector going with a theory that the bigger breaker could theoretically allow someone in the future to add more backfeed at the remote panel without them tripping that 70A breaker.)

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                        • #13
                          Originally posted by foo1bar View Post


                          I *think* there's some weirdness in one of the versions of NEC that it could be interpreted that you need to use the 70A in your 120% rule calculations on the main panel.
                          The calculation of the 120% rule in recent cycles is pretty clear that the OCPD size at the inverter is used for all busbar calculations, and was replaced with using 125% of the inverter's rated output current in 2014 NEC.

                          The weirdness that I'm aware of relates to sizing the feeder to the sub panel. There are cycles and interpretations that would require it to carry both the 70 A from the main panel and the 30 A from the PV, or 100 A total.
                          CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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                          • #14
                            Originally posted by foo1bar View Post
                            I assume that both the 70A will be at the opposite end of feeder for it's busbar, as well as the 30A will be at the far end from the lugs on it's busbar

                            I *think* there's some weirdness in one of the versions of NEC that it could be interpreted that you need to use the 70A in your 120% rule calculations on the main panel.
                            1> figure out which version of NEC you're on.
                            2> draw up your plans exactly as they'll be installed and talk to the plan inspector to make sure what you're planning is fine. (logically it's obvious you'd only have 30A backfeed at the main panel. But I could see a plan inspector going with a theory that the bigger breaker could theoretically allow someone in the future to add more backfeed at the remote panel without them tripping that 70A breaker.)
                            I'm not sure how it would make any difference.. If there's a 70 amp breaker, the wire can't pass more than 70 amps in any direction either coming from the main panel or being back fed from the sub panel.

                            Even if someone hooked up a generator to the sub panel, there's no way to back feed more than 70 amps through that 4ga wire because it has a 70amp breaker on it. Now you could hook up a generator and feed much higher amperage into the sub-panel and then into the various breakers and connected loads, but you could do that with any panel.. and so long as each circuit has a breaker, the amperage can't exceed what the wire can carry.

                            Am I missing something?

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                            • #15
                              Originally posted by Murby View Post

                              I'm not sure how it would make any difference.. If there's a 70 amp breaker, the wire can't pass more than 70 amps in any direction either coming from the main panel or being back fed from the sub panel.

                              Even if someone hooked up a generator to the sub panel, there's no way to back feed more than 70 amps through that 4ga wire because it has a 70amp breaker on it. Now you could hook up a generator and feed much higher amperage into the sub-panel and then into the various breakers and connected loads, but you could do that with any panel.. and so long as each circuit has a breaker, the amperage can't exceed what the wire can carry.

                              Am I missing something?
                              What you are missing is that the earlier versions of the NEC assume that you could someday have either a fault or a newly installed load attached somewhere along the length of the feeder which would take power from both ends and therefore would not be protected by OCPD at either end.
                              This unrealistic assumption was effectively rejected in the 2017 code version.
                              SunnyBoy 3000 US, 18 BP Solar 175B panels.

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