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  • junction between PV cables and THWN in conduit

    So many questions, I've searched but no definitive answers ...

    In my ground-mount, I'm trying to figure out the transition from the MC4-connector cables on the panels (which I'll connect into two strings) to the THWN conductors which will run in buried conduit to where the string inverter is located on the side of the house (near the load center). The conduit run will consist of a 10awg ground, and two DC pairs in either 10awg or 12awg. I've already buried an "L" of 1-1/4" PVC conduit in one of the footing/piers for my system (so it sticks up vertically beside one of the 6x6 posts, and emerges from the side of the pier at the 18" depth required for the conduit run).

    Clearly I need some sort of waterproof junction box, at least 9*2.5 = 22.5 cu-in (but hopefully a bit larger). I doubt I'll find one with a 1-1/4" opening (dunno if it's called "knockout" in a PVC box) that's not enormous and expensive, so I'll have to reduce that vertical PVC from 1-1/4" to 3/4". It also needs openings for the various wires that enter it, the 4 conductors for the two strings, and ground. I believe these openings require things called "glands" to seal where they enter the box. Is it one gland per conductor, so 4 for the DC pairs, and one for ground if it runs inside the conduit ?

    I'm unclear on the ground. I'll have bare solid 6awg running between clamps on the IronRidge rails and to a ground rod. Somehow I need to connect the conduit ground wire to this system. My inclination is to make the 10awg conduit ground wire be stranded and insulated and run inside the conduit; is this correct ?

    Sounds like for making the connections, wire nuts are considered to be questionable, unless they're the silicon-filled type. Maybe terminal strips are better ? If so, how to mount in the box, or just floating in there ?

    I'd appreciate comments on whether I have all this right, and pointers for buying the junction box, glands, connectors.


  • #2
    20200512_121245.jpg This works. You can get boxes of any size at a home center or hardware store. This is a 4 X 4 and deep. Note the label. I drilled the holes for the conduit, the glands and ground. I know they make models in 8 X 8 and 12 X 12. I think the manufacturer is Carlon.
    Inside I use a silicon filled connector called a Tap Conn. I found it at a home center and it floats inside. I am trrying to find a phote. It was about $3.00 Note the glands on the solar panel cable and they loop down then up for a drip loop. The copper ground is barely visible and doesn't use a gland because the hole at the bottom provides a way for moisture to escape. No matter how waterproof they are water can enter just through moisture in the air and condense.
    Last edited by Ampster; 05-12-2020, 03:30 PM. Reason: Add another photo
    9 kW solar. Driving EVs since 2012

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    • #3
      For the connectors, maybe you mean DryConn: https://www.lowes.com/pd/DryConn-Aqu...ectors/3377352

      Drip loop is a great idea. Do you have a link for that (or similar boxes) ? I need more openings for my two strings. I'm not sure NEC allows "modifying" a part by drilling holes; duh, I guess you have to though, because most of the boxes I've found have no holes or knockouts at all.

      I don't see the copper ground at all; you ran the copper inside the conduit ? But if the hole at bottom allows moisture to escape and that's good enough for the ground, which opens into the same box, seems kinda like you don't really need gland for PV wires either.
      Last edited by RShackleford; 05-12-2020, 03:53 PM.

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      • #4
        Like you, I was taught to never modify electrical components, as that violates the listing. But I'm not certain the exact wording on modification in the code.

        One of the vendors of these sealed boxes is Cantex. That's the brand carried by many big box stores. This video from the Cantex website is instructions for installation these boxes and specifically directs you to cut holes in the sides of the box. I guess that means that the box will not be modified by cutting holes, because that is the intended use method, just like knocking out metal coins.
        https://youtu.be/we5Y--w6fcw
        Cantex sells the same basic box in sizes from 4x4x2 to 12x12x6, and all carry UL listing and NEMA ratings for types 1, 3, 3S, 4, 4X, 5, 6, and 6P. NEMA 6P is pretty darn good, allowing "prolonged submersion at a limited depth". Cantex part numbers are 51337xx, where xx is two digits to specify the specific size box. Their catalog says:
        UL Category QCUP
        UL File #E205935
        Control #92CM
        I have no clue what all of that means.
        7kW Roof PV, APsystems QS1 micros, Nissan Leaf EV

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        • #5
          I tried to post a link and details but it delayed in moderation. In the meantime here is a photo and the name is Alumiconn alumiconn-wire-connectors-wire-terminals-95125-0-64_1000 (1).jpg
          9 kW solar. Driving EVs since 2012

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          • #6
            Originally posted by Ampster View Post
            I tried to post a link and details but it delayed in moderation.
            Yeah, this site does some annoying stuff. The latest thing is it seems to want me to log back in almost every time I come back to the site, multiple times per day when I'm this active in a thread.
            In the meantime here is a photo and the name is Alumiconn alumiconn-wire-connectors-wire-terminals-95125-0-64_1000 (1).jpg
            Looks nice, but it's only rated to 300v - not high enough for most string-based systems. Those DryConn's are 600v, cheaper, and seem like they'd work well.


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            • #7
              When I had a similar wiring problem, I elected not to run the big ground into my sealed junction box. My ground wire was AWG 6 stranded, and there was no feasible gland for stranded bare wire. I just ran the ground along the conduit with cable ties and to the ground rod. In retrospect, it would have been smarter to get insulated ground wire, but I would have still run it outside of the conduit.

              Yes, Alumiconns and DryConns are both very good. You could also check out Marathon 985-GP-xx connectors, where xx is the number of isolated circuits. These are rated 85A, 600VAC/DC. For example, a 985-GP-04 has four separate circuits, and each circuit accepts two large wires up to AWG 4 or multiple smaller wires. These are available from electronic distributors and also some dealers on Amazon, but not big box stores. Google the part number for specs and dealers. Here's a photo of a 985-GP-04, which is like four 600V 2-wire Alumiconns in one plastic block:
              9152946962462.jpg
              7kW Roof PV, APsystems QS1 micros, Nissan Leaf EV

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              • #8
                The more expensive NSI brand ones are rated for 600 volts. I did not realize the Dri Conns were good for 600 volts since I use them regularly for sprinkler wires. I am still not a fan of wire nuts and may swap out for the NSIs. I know @Mike90250 has an opinion on wire nuts.
                9 kW solar. Driving EVs since 2012

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                • #9
                  Last time I looked, NSI Polaris connectors were quite expensive, but good.
                  7kW Roof PV, APsystems QS1 micros, Nissan Leaf EV

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                  • #10
                    Originally posted by bob-n View Post
                    Here's a photo of a 985-GP-04, which is like four 600V 2-wire Alumiconns in one plastic block:
                    9152946962462.jpg
                    That looks perfect for my two strings, but about $20 to get one to my doorstep. The NSI Polaris are crazy expensive.

                    I think I'll try those DryConn wirenuts first. Don't understand mistrust of wirenuts. Yes, it's a potentially damp location, but the silicon seal seems to address that; a little confused how that works (in the DryConn) though. Almost seems like you could just use a regular wirenut and squirt some silicon caulk in there.
                    When I had a similar wiring problem, I elected not to run the big ground into my sealed junction box. My ground wire was AWG 6 stranded, and there was no feasible gland for stranded bare wire. I just ran the ground along the conduit with cable ties and to the ground rod. In retrospect, it would have been smarter to get insulated ground wire, but I would have still run it outside of the conduit.
                    How come outside the conduit ? I'm thinking I'll make my ground be 10awg/insulated/stranded, run it inside the conduit. Then just bring it outside the j-box through an appropriate gland, and tie it to the 6awg solid wire with a clamp-style connector.



                    Last edited by RShackleford; 05-12-2020, 08:23 PM.

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                    • #11
                      For ground, inside is fine and outside is fine. Whatever works in your system is fine.

                      I was thinking of the ground connected to the rails and panel frames. That wire goes directly to the ground rod(s). The house has another wire from ground rod to panel. In the event of a nearby lightning strike, we want the high-current pulse collected by the panel frame going right to earth, not going through other cables or the house wiring.
                      7kW Roof PV, APsystems QS1 micros, Nissan Leaf EV

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                      • #12
                        Originally posted by bob-n View Post
                        I was thinking of the ground connected to the rails and panel frames. That wire goes directly to the ground rod(s). The house has another wire from ground rod to panel. In the event of a nearby lightning strike, we want the high-current pulse collected by the panel frame going right to earth, not going through other cables or the house wiring.
                        Oh yeah, I'm doing that too - 6awg/bare/solid connecting the rails directly to a ground rod. Only question is best way to get wire coming from inverter (or main load center) to PV array connected to the 6awg.


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                        • #13
                          One ground wire from load center to ground rod. This is already in place before installing solar.
                          One 6-AWG ground wire from rails to ground rod.
                          One ground wire from load center to inverter. There will be a large screw-strip in the load center for grounds. You can simply run red/black/green THWN from inverter to load center. Red & black go to the breaker and green goes to the ground screw-strip.
                          7kW Roof PV, APsystems QS1 micros, Nissan Leaf EV

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                          • #14
                            Originally posted by bob-n View Post
                            One ground wire from load center to ground rod. This is already in place before installing solar.
                            One 6-AWG ground wire from rails to ground rod.
                            One ground wire from load center to inverter. There will be a large screw-strip in the load center for grounds. You can simply run red/black/green THWN from inverter to load center. Red & black go to the breaker and green goes to the ground screw-strip.
                            I'll actually put a new ground-rod in at the array.
                            The SunnyBoy wants a neutral connection too; I might run Romex, because the inverter is probably gonna be on the outside wall of the house, and the wires come out the bottom of the inverter, so it may easiest to go down into the crawlspace (using conduit) through the band joist, and then over and up into the load center - so pulling Romex through conduit that short distance may be easier than adding a box inside the band joist to transition from THWN to Romex (or running conduit all the way to the load center.


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                            • #15
                              I've seen too many scorched twist on wire nuts to be able to endorse them. Terminal blocks, polaris or split bolts are much more secure and less prone to invisible errors inside the spring cap.


                              > Almost seems like you could just use a regular wirenut and squirt some silicon caulk in there.


                              NOOOO !!!! Silicone caulk is corrosive to copper, it has a vinegar component to the cure cycle (smell it sometime) The expensive electrical cable rated caulk uses a neutral cure.

                              The weatherproof wire nuts use silicone GREASE in them.
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