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junction between PV cables and THWN in conduit

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  • #16
    The kinginnovations website doesn't show any such animal as a 600v-rated Alumiconn; I guess people are talking about the similar (but more expensive) NSI Polaris ?

    Thanks for the wire-nut wisdom @Mike90250.

    Thinking that 4-port 985-GP-04 is the way to go.

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    • #17
      Originally posted by RShackleford View Post
      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.
      Definitely is allowed.
      Holes should neat and tidy of course - the whole "neat and workmanlike manner" rule.

      If you're doing PVC conduit (which it sounds like you are) I would make sure to put the hole far enough from the walls of the box. You want to be able to insert the "box adapter" through the hole to connect into the female PVC conduit opening that you're connecting to. If It works out nicely I have the bell-end of the conduit against the box, I think it looks nicer than a coupler - but sometimes you need to go into an LB or use a conduit coupling. BTW, I've been able to make some nice bends with a big pot of boiling water to heat the conduit - it's barely hot enough, but better that than winding up with a scorch mark.

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      • #18
        Originally posted by foo1bar View Post
        Definitely is allowed.
        Holes should neat and tidy of course - the whole "neat and workmanlike manner" rule.

        If you're doing PVC conduit (which it sounds like you are) I would make sure to put the hole far enough from the walls of the box. You want to be able to insert the "box adapter" through the hole to connect into the female PVC conduit opening that you're connecting to. If It works out nicely I have the bell-end of the conduit against the box, I think it looks nicer than a coupler - but sometimes you need to go into an LB or use a conduit coupling. BTW, I've been able to make some nice bends with a big pot of boiling water to heat the conduit - it's barely hot enough, but better that than winding up with a scorch mark.
        I've always used "male adapters" before - stick through the hole, apply a nut (and a rubber washer in this case, since it's exposed to elements), and then you can glue straight conduit (not a bell end) to it.

        As far as bending ... when I stuck that "L" conduit assembly into the form-tube for the pier nearest the house, it didn't come out quite right where it emerges from the concrete below grade. It's pointed maybe 20 degrees off from the direction I'm digging the trench to the inverter location. Not sure how to address. Was thinking to take a 45-degree elbow and just cut it off where the angle is right, but that would end up being not too far from the bell, and I'm not sure the cross-section is circular enough there for the bell of the next 10' length to fit over it. Maybe I should forget the elbow, just use a full section and bend it first. Or try to bend the elbow first. What do you recommend ?

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        • #19
          Forgive what is probably a stupid question, but is there a reason we don't use a larger junction box and use MC4 connectors to connect the string from the array to the wires going to the Inverter?

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          • #20
            Originally posted by scrambler View Post
            Forgive what is probably a stupid question, but is there a reason we don't use a larger junction box and use MC4 connectors to connect the string from the array to the wires going to the Inverter?
            If inverter is far away (on side of house, 30ft from my ground-mount array), I want to use regular wet-condition conduit wire (THWN) for that long run; MC4 terminated PV wire is kinda expensive and I'm not even sure it's rated for buried conduit. Given that, I suppose MC4 connectors could be used in junction box, if able to join them to THWN wire; and given that all the MC4 connections between panels are completely exposed, that might eliminate the need for any junction box at all (but at some point the wire has got to enter conduit, as it goes underground).

            Anyhow, what I plan to do (and I gather would be considered standard), is to buy a couple of cords with MC4 connectors at the ends, and cut those cords in two. Those would connect to the MC4 connectors at the ends of my two series strings of panels. The bare wires (from the cut cords) would go into the j-box through "glands". There I'll join the bare ends to the THWN wire that leads into the conduit, using one of the several methods debated above.


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            • #21
              I was assuming (maybe wrongly) that you can Crimp an MC4 Connector onto the regular wire used to pass in a conduit down to the Inverter.
              Still using a box to have a clean connection with the conduit.
              I was wondering if the Quality of the MC4 connector would not be better than any nut or terminal usually used in these boxes

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              • #22
                Originally posted by scrambler View Post
                I was assuming (maybe wrongly) that you can Crimp an MC4 Connector onto the regular wire used to pass in a conduit down to the Inverter.
                Still using a box to have a clean connection with the conduit.
                I was wondering if the Quality of the MC4 connector would not be better than any nut or terminal usually used in these boxes
                Do there exist crimpable MC4 connectors ? If the quality of the MC4 connection isn't good enough, then we're in real trouble, because when using string inverters there are a bunch of MC4s in series. Curious what the wise heads here think of this approach. If reasoanble, seems like the box could be dispensed with, since obviously the MC4-MC4 connections don't need to be in an enclosure; the only issue is how to reasonably seal the end of the conduit where the THWN passes into it.



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                • #23
                  Originally posted by RShackleford View Post
                  ; the only issue is how to reasonably seal the end of the conduit where the THWN passes into it.
                  You could use a rain head but where are you going to transition from exterior wire to THHN. You have to use a junction box for that connection because you can't put a splice in conduit.
                  9 kW solar. Driving EVs since 2012

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                  • #24
                    MC4 connectors can definitely be crimped, as far as I know this is how they make the custom length cables when connecting panels.
                    I would still use a Junction box to get a clean, sealed and long lasting connection with the conduit.

                    You want this to last forever in harsh weather conditions, so you don't want to cheap out on that part.

                    Any views from the experts on MC4 inside the junction box?

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                    • #25
                      Originally posted by Ampster View Post
                      You could use a rain head but where are you going to transition from exterior wire to THHN. You have to use a junction box for that connection because you can't put a splice in conduit.
                      Ok, so the interesting suggestion of @scrambler boils down to a possible additional possibility for the PV-wire to THWN connection (in addition to the several mentioned earlier in this thread); the junction box must still be there.


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                      • #26
                        "Any views from the experts on MC4 inside the junction box?"
                        Not an expert.
                        But I wouldn't use an MC4 connector inside a junction box.
                        IMO it'd look weird.
                        It also probably is less cost effective than other connectors that could be used and be just as effective.
                        And I don't think it'd seal properly on the THWN like it does on PV-wire (probably not a critical thing since it'd be inside a junction box)

                        "since obviously the MC4-MC4 connections don't need to be in an enclosure;"
                        If one side is THWN, they probably aren't weathertight like they are with PVWire. So I'd want it in an enclosure. And THWN can't be outside of an enclosure/raceway - so you'd have to have one anyhow.

                        "MC4 terminated PV wire is kinda expensive and I'm not even sure it's rated for buried conduit."
                        PVWire isn't usually dual-rated for direct burial, but I believe that buried conduit is just the same as any "Wet" location so I think PVWire could be run inside buried conduit.
                        (You'll have to do the conduit fill calculations - so need to know the size of the wires since they aren't as standard as thwn)

                        "Anyhow, what I plan to do (and I gather would be considered standard), is to buy a couple of cords with MC4 connectors at the ends, and cut those cords in two. Those would connect to the MC4 connectors at the ends of my two series strings of panels. "
                        Reasonable approach.
                        I bought PVWire and bought a high quality MC4 crimp tool. But your approach should be workable too. You'll probably want to pre-plan the wiring so you have the right lengths. And plan for some waste in your PVWires. But it's a reasonable plan.

                        "when I stuck that "L" conduit assembly into the form-tube for the pier nearest the house, it didn't come out quite right where it emerges from the concrete below grade. It's pointed maybe 20 degrees off from the direction I'm digging the trench to the inverter location"
                        ...
                        "Maybe I should forget the elbow, just use a full section and bend it first. "

                        There are 22 degree elbows.
                        But I'd probably just bend the end of a full section.
                        Think about how you're going to get it hot enough to be flexible. I've used boiling pot of water and I've used heat guns and I've used propane torches. A boiling pot of water will not get too hot and wind up with a scorch mark, but can't be applied to something in the middle easily. The conduit starts firming up very quickly when you take it out of the water - the evaporating water cools it quickly and it's just into the flexible temperature to begin with. If you've got a turkey fryer (big pot, big big burner to use outdoors) that'd probably work well. - can stick the conduit in without having to worry about hitting the ceiling.
                        And think about how you're going to measure to get the right bend. If you're right by your trench, you can check right where it's going to be. if you're inside, you probably want some sort of template or something to get your bend to be close and not have to bend it numerous times.

                        If you do a more direct heat source like a heat gun or torch, it's easy to scorch/burn the conduit. I've had to throw out a few attempts where the color went from grey to brown. (oops) Even had one where it had some black.

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                        • #27
                          Thanks for confirmation my plan is good; and I found one of those 985GP04 terminal blocks on ebay for $10, so that's covered. Seems like it'll be easier to deal with if it's fixed in place, and it doesn't have screw mounting ears, but maybe I can epoxy it to the bottom of the j-box.

                          On bending PVC, the bend needs to be near the end, so shouldn't be too bad to get into a pot on boiling water. But I've been wanting to buy a heat gun. Would be the second tool that this project has given me excuse to buy, and that's always a good thing . But a 22-degree elbow sounds a lot simpler, probably close enough, with the wiggle one can put into a joint ...

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                          • #28
                            Depending on the PVC diameter, you can get these flexible couplings, they will easily bend to what you want.
                            https://www.lowes.com/pd/Dura-Plasti...E&gclsrc=aw.ds

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                            • #29
                              Originally posted by scrambler View Post
                              Depending on the PVC diameter, you can get these flexible couplings, they will easily bend to what you want.
                              https://www.lowes.com/pd/Dura-Plasti...E&gclsrc=aw.ds
                              There's also this one(hose with clamps), which. is the 1-1/4" size I'm using (yeah, oversized for five 10awg wires, but it's cheap and makes things easier). Thing is, I believe this, and the one you linked, are meant for plumbing PVC. Dunno if they are fit-compatible, and if they are listed, for use with electrical conduit.

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                              • #30
                                Not exactly sure which conduit you are using, there are also some flexible electrical conduit with compatible connectors. Something like below maybe
                                https://www.google.com/search?q=elct...egtQXEtK7wBw50

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