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Electrical help

Post in 'DIY and General non-hearth advice' started by nate379, Jan 25, 2013.

  1. nate379

    nate379 Guest

    I got my solar setup inspected by the power company and I need to add a disconnect switch at my outbuilding.

    The disconnect is a Square D DU221RB http://www.altestore.com/store/Encl...-DU221RB-30A-240VAC-Unfused-Disconnect/p4165/

    I was thinking about mounting it on a J block (have vinyl siding on the building) and running the wiring through the back. There is one knockout on the back. Is it ok to run 2 wires through 1 knockout and grommet??



    Right now I have a 12/3 wire running from the "attic" in the building coming from my panels over to my breaker panel and connected to a 20 amp breaker.

    What's the easiest way to include this disconnect switch in this circuit without running a new wire from the solar panels?

    I have finished walls in the outbuilding so it wasn't too easy to route a wire into the panel, and won't be easy to run into the disconnect either.
    I was thinking maybe of making a junction in the panel as much as I hate to do it. Pull the wire off the breaker and make a junction that goes out to the disconnect. Then the wire coming back from the disconnect would run into the breaker.

    One last thing, the disconnect box doesn't have any obvious area to attach a ground wire. Is that normal? I thought it was odd that neutral isn't disconnected either, but this disconnect is a common one to be used on PV panels and the power company said it would work fine.

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  2. StihlHead

    StihlHead Guest

    Neutral is essentially ground, so there is no disconnect for that. You always want your white wire bonded to the panel box white bus bar with no interruptions. All you are disconnecting/interrupting with the switch box are the two poles: the red and black 120v phases that are hot.

    To ground the disconnect box get the grounding lug that they are advertising with it and bond that to the box (screw it into one of the holes in the back of the box), and run a ground wire to that. That is all you need. You do not need a neutral or ground wire in the disconnect run. Only one ground to the box from a grounding rod or from the panel box ground bus bar (use whatever size ground wire is required for code these days for that). You should be able to use 12/2 wire to and from the panel as you are planning, and mark the white wire red on both ends. It is similar to running a switch with one x/2 wire from a light box with power run to it first. You wire nut the white wire to the white side of the light and wire nut the black wire to the black wire running to the switch. That black wire is connected to one side of the switch, and the white wire is connected to the return line where it is wired to the black side of the light outlet. In that case, you use black tape on or mark both ends of the white wire running to the switch with a black marker to designate that it is hot and not neutral.

    That is essentially what you are doing with your circuit. You are running a line to and from the panel to the disconnect. Just use the right size wire and wire nuts. You can run more than one wire through a knockout, just make sure that you lock them where they enter the boxes (there are many types of knockout wire locks, some are plastic, and some have metal clamps). If you have any extra bare ground wires at either end, just bond them to the panel ground bus bar.
  3. begreen

    begreen Mooderator Staff Member

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    Stihl, are you sure about bonding the neutral to the box? I thought in WA state that the neutral bus must be isolated, independent of the ground. Nate, is this 240vac coming from the panels thru enphase inverters? If so, there is no neutral involved, just two hots.

    As for the other questions, I'm hesitant to answer without a clearer visual picture of the setup. When you ask about 2 wires are they in flex conduit or is this NM cable? When you say 12/3 do you mean 2 wires and a ground or 3 wires and a ground? Do you currently have them routed direct to the breaker in the panel? A picture or two would help here.
  4. nate379

    nate379 Guest

    Ok.... had to edit cause stuff got posted before I could post.


    Neutral isn't bonded to ground at my panel since it's a sub panel.

    There was something I was reading where there was worry that no disconnect on the neutral could in some way feed power or leave it floating. I can't remember exactly, but I think it applied to generator disconnects, which this sorta falls under.
    In any case the disconnect is correct for my application according to the power company, that's mostly what I need to worry about.

    I'm using NM wire. 12/3 from the Enphase inverters to the breaker panel that is in the shed. 2 hots, 1 neutral and a ground. Also a #6 ground that ties all the panels and inverters as well.

    I have a main disconnect at my house and I expected that it would be fine as a disconnect. Power company didn't agree, wanted a separate disconnect switch at the outbuilding so that's why I'm rewiring.


    A regular #12 ground wire.. (ie the one in the NM wire) from panel to disconnect will be ok? I have #6 run from the 2 ground rods to the panel.

    2/1 wire as in 2 hots, 1 neutral? I might end up doing that, Pretty sure I have a roll of 12/2 left over from when I wired the outbuilding.
    I could probably source a 4 conductor NM wire, like a 12/2/2 though I don't know how common it is.

    Is it ok to run more than 1 wire through a knockout? I'm using the plastic bushings kinda like these http://www.elliottelectric.com/Products/Detail.aspx?v=ARL&c=NM96

    I kinda have in mind how to get this all done, just wanted to pick some brains to make sure I'm doing it the best/easiest way.
  5. begreen

    begreen Mooderator Staff Member

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    You are not answering the questions. It's hard to follow and could be unsafe to answer without an accurate picture. Gen wiring is a non-applicable tangent.

    You said you have 12/3 coming from the panels but it sounds like you may have 12/2 NM (which has a black wire, a white wire and a bare ground wire). That's the first thing I'm trying to get clear so that I can answer the question about the bushing. Do you intend to butt the disconnect right next to the breaker panel with a 1/2" knockout connecting them?
  6. nate379

    nate379 Guest

    disco.jpg Img_0058.jpg Yes it's 12/3 NM. 2 hots, 1 neutral and a ground.. black, red, white and copper.

    The breaker panel is inside the building and the disconnect will be outside. Give me a sec and I'll see if I have any photos to put up here.

  7. StihlHead

    StihlHead Guest

    I am not saying bond neutral at the solar panel box, or at the disconnect box, but that it will be bonded at the main service box. My read is that he has a new 220v circuit running to and from the main service bus to a solar panel box. As such, the neutral is going to be bonded at the main service box (to ground), and the 2 poles there lead to a breaker. He can either disconnect the 2 hot poles in the main service box and add a run to and from the disconnect box, or he can disconnect the 2 poles in the solar panel box and run lines to and from the disconnect and splice them there. Either way it adds a disconnect to the 2 poles. He could also run a 12/3 from the solar panel to a disconnect, and 12/3 from the disconnect to the main panel, in which case the neutral would be wire nutted through and not bonded to the disconnect box. But that would take more wire... romex is not cheap these days, and he already has the 12/3 wire run in place.

    The solar panel and the additional breaker panel is not going to be bonded (to neutral) and there will not even be a neutral in the disconnect loop with the first two options. Standard 12/3 is one ground and 3 lines; red, black and white. 12/2 is one ground and white and black. Conduit or bendix line does not matter, as long as it is inside a waterproof building. Otherwise it has to be run in exterior grade Romex, regardless.
  8. StihlHead

    StihlHead Guest

    If I am seeing your photos right, all you have to do is add a short 12/2 wire pair run from the solar panel box (I am assuming that is the box next to the door) to the disconnect on the other side of the wall. Then just splice the wires inside the solar panel box so that they disconnect the solar panels from the solar box, or the solar panel from the main panel (I am not sure which you need here, but you can wire it either way).
  9. begreen

    begreen Mooderator Staff Member

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    Ok, got your additional info now. We're cross-posting. So do you want to tie the back of the breaker panel to the back of the disconnect switch? Is that correct? Have you checked to be sure that the exterior location ok with your inspector? I don't know, but would ask first. Enphase uses the neutral as a communications link according to their docs. Does the inspector wants the neutral from the Enphase also switched at the disconnect?

    Running a couple of #12 wires through a 1/2" close nipple is fine. I have used something like this: http://www.grainger.com/Grainger/RACO-Chase-Closed-Nipple-3LP48?Pid=search Use an all weather disconnect and a longer nipple with no J box.
  10. nate379

    nate379 Guest

    The box in the shed is the subpanel that feeds the whole building (lights, outlets, 240v air compressor, etc) The solar panels are connected into that box.

    Looks real easy to do in that pic, but that was before I insulated and sheathed the walls ;)

    It's not so much an inspector but rather an engineer from the power company. He just did a quick check to make sure my system was safe to feed power into the grid (that's all they care about).

    The location was ok'd with him and the disconnect box is fine with him as well. I was just asking about the neutral as an FYI for me.

    I need to measure, but I think I'll be able to put the disconnect in the same stud cavity but more or less under the panel. It should put that switch at around 5ish feet from the ground.
    I could possibly do back to back but there are no knockouts on the back of the breaker panel. I wasn't sure if it's allowed to just make my own so I wasn't really considering it.
  11. StihlHead

    StihlHead Guest

    Yah, you are better off going under the sub panel to the disconnect. There are no wires there to get in the way in your photo (but there are above). I would use a hole saw for doorknobs and drill out below the inside wall of the panel, giving yourself enough room to do the wiring. Then when you are done wiring attach a 4 inch wood slat behind the hole and screw it with drywall screws on either side, and screw the hole cut out to the center of the slat. I have done that many times with many types of materials (rock, paneling, OSB, & plywood). It also can be later removed and fixed or inspected if they give you any shyte. The engineer will just want to see that it works, and not likely care how it is wired. County/state code enforcement will not care if an engineer is signing off on it.

    Solar in Alaska? Man, I thought that the 45th parallel was way too high for any ROI on solar. We get a lot of cloud cover here though. I measured 850 watts per square meter at noon on a clear day during the week of the winter solstice. With snow cover a week later on a clear day it shot up to 1100 watts. With any overcast it goes under 100 watts.
  12. begreen

    begreen Mooderator Staff Member

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    Reading back over this thread Stihl, you were exactly correct. I should not try answering questions at that hour. Way past my normal bedtime.
  13. nate379

    nate379 Guest

    I should be able to fish tape from outside into the bottom of the box. Worst case I'll cut a small hole in the exterior OSB to where I can nail it back in place. Little tuck tape over the house wrap and will be good as new.

    Was going to knock it out this weekend but it got colder than heck. Didn't want to chance trying to pull the vinyl at -15* not to mention the wire is near impossible to work with at those temps. Have had the sheathing just BREAK off before!

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