Wiring solar panel on the roof while waiting for inverter delivery

mi_cinmi_cin Registered Users Posts: 8
Hello there,

I have chosen a grid tie pv installation. Right now I have some guys on the roof installing mounting system. I ordered an inverter and I'm still waiting for a delivery.

Can the roofers install the panels and connect them together in the string (16 panels in the string, 29Vmp each) and leave it like that till the inverter come? I don't know if isn't that risky to have 464V hanging in the air on the roof? I just don't want to call them again next month, pay for their trip, time to build scaffolding again etc.

If they are on the roof now can they install everything, connect pv in series, leave just two wires (+ and -) and go home?

Marcin

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Wiring solar panel on the roof while waiting for inverter delivery

    They could install everything right up to where the inverter will be wired in. No connections on the install should be exposed, so any "loose wires" would be inside some type of junction box.
  • jaggedbenjaggedben Solar Expert Posts: 230 ✭✭
    Re: Wiring solar panel on the roof while waiting for inverter delivery

    It is fine to connect the panels together. Just do not connect them to any other wiring that does not have a connector at the other end.

    Here is what I would do:

    -Choose which end of the string will be the end with the junction box. Make this the positive end, leave the positive lead of that panel unconnected.
    -Run a "home run" wire from the opposite end of the string. You'll need to buy or make a USE-2 wire with a positive and negative connector. Plug the negative lead from the last panel into this wire, and bring the positive end of the wire to the junction box location.
    -Connect the rest of the panels in series, give your guys their money.
    -When you install the junction box, install two 'pigtails' into it, one with a positive connector and one with a negative. You'll need to buy or make a short USE-2 wire and cut it in half. Do NOT plug these in yet.
    -Splice the pigtails in the junction box and complete all the rest of your DC and AC wiring to the inverter.
    -Plugging the pigtails into the array is the very last thing you do,

    For a small additional cost in connectors, this is the safest and most convenient way to go about it.
    Alternatively, you could run the negative "home run" wire all the way from the junction box to the opposite end of the string, without the pigtail. But this means you have to leave it unplugged and then get under that panel when you are all done, which may not be convenient.
  • jaggedbenjaggedben Solar Expert Posts: 230 ✭✭
    Re: Wiring solar panel on the roof while waiting for inverter delivery
    They could install everything right up to where the inverter will be wired in. No connections on the install should be exposed, so any "loose wires" would be inside some type of junction box.

    The way you said that, I don't agree. They need to leave at least the ungrounded conductor unconnected on the roof.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Wiring solar panel on the roof while waiting for inverter delivery
    jaggedben wrote: »
    The way you said that, I don't agree. They need to leave at least the ungrounded conductor unconnected on the roof.

    No, I disagree; the ground should be connected solidly. As per NEC's DC GFI regs the panel frames/mounts would be connected to Earth ground which has nothing to do with the inverter install. The power leads from the array would be connected via the ground fault breakers, which should have its ground connected to the AC grounding system. No reason to leave grounding disconnected just because the inverter is not installed; it carries no current under normal conditions and does not present any hazard.
  • jaggedbenjaggedben Solar Expert Posts: 230 ✭✭
    Re: Wiring solar panel on the roof while waiting for inverter delivery
    No, I disagree; the ground should be connected solidly.

    I didn't say it shouldn't be, but realistically this won't be done until the inverter is installed, because the array EGC will be typically be terminated in the grounding bar in the inverter's integrated disconnect.
    As per NEC's DC GFI regs the panel frames/mounts would be connected to Earth ground which has nothing to do with the inverter install.

    Usually grounding on GT inverters is done according to 690.47(C)(3) in which case it makes all the sense in the world to wait until the inverter is installed.
    The power leads from the array would be connected via the ground fault breakers, which should have its ground connected to the AC grounding system. No reason to leave grounding disconnected just because the inverter is not installed;

    Again, you're not making sense, since the ground fault system is typically all in the inverter.

    Did you read this thread too quickly? Did you think we're talking off-grid instead of grid tie?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Wiring solar panel on the roof while waiting for inverter delivery

    Nope. If you don't know what the inverter is exactly (for instance a hybrid GT which uses a charge controller and batteries) you shouldn't assume anything on the panel output.
    I was merely stating that the panel frames & mount should be grounded now, while they're at it, as this is independent of the inverter.

    The grounding for the DC GFI is a matter of where it is located; internal of the inverter or external before it (either with or without a charge controller, depending on system). That is the ground which goes to the AC grounding rod and probably can not be connected until the inverter is installed because it will depend on which inverter and usually such wiring is 'daisy chained' back to the main panel.
  • jaggedbenjaggedben Solar Expert Posts: 230 ✭✭
    Re: Wiring solar panel on the roof while waiting for inverter delivery

    To get back to the OP's question...
    mi_cin wrote: »
    I have chosen a grid tie pv installation. Right now I have some guys on the roof installing mounting system. I ordered an inverter and I'm still waiting for a delivery.

    What kind of inverter have you ordered? Is it coming with an integrated DC disconnect?

    If it is not coming with a disconnect, then you could go head and install your DC disconnect, run the wiring to the disconnect, and then plug in the array to the wiring (make sure the disconnect is off!!). You could fully wire the disconnect and leave the wiring to the inverter hanging out somewhere. This would allow you to avoid going back on the roof after you install the inverter (unless you need to troubleshoot). Follow the instructions in my first reply above, just replace 'inverter' with 'disconnect'.

    If your inverter is coming with a disconnect, it's probably not worth installing a second one, so just wait until it comes.
  • jaggedbenjaggedben Solar Expert Posts: 230 ✭✭
    Re: Wiring solar panel on the roof while waiting for inverter delivery
    Nope. If you don't know what the inverter is exactly (for instance a hybrid GT which uses a charge controller and batteries) you shouldn't assume anything on the panel output.

    And if you don't whether there is a CC and breakers or not, which you don't, then you shouldn't state that "They could install everything right up to where the inverter will be wired in." You could be telling him to energize his conductors to 600V before they are terminated anywhere. That's precisely what we should be advising him not to do.
    I was merely stating that the panel frames & mount should be grounded now, while they're at it, as this is independent of the inverter.

    No, it's not independent of the inverter, it depends what equipment specifically he is waiting for, whether it includes a disconnect and so on.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Wiring solar panel on the roof while waiting for inverter delivery
    jaggedben wrote: »
    And if you don't whether there is a CC and breakers or not, which you don't, then you shouldn't state that "They could install everything right up to where the inverter will be wired in." You could be telling him to energize his conductors to 600V before they are terminated anywhere. That's precisely what we should be advising him not to do.

    Wrong. All GT arrays are required to have a disconnect. Nothing would be energized. Without a completed circuit a panel's output is zero.
    No, it's not independent of the inverter, it depends what equipment specifically he is waiting for, whether it includes a disconnect and so on.

    Wrong again. The disconnect is required to be outside and accessible which the inverter may or may not be (preferably not). You could in fact put in everything except the inverter and it would all be perfectly safe. The biggest danger would be from the AC mains, for which you leave the back-feed breaker out.

    The only way such a set up could be dangerous is if someone started poking around inside it where they don't belong. That is dangerous with any power system in any state of assembly.
  • jaggedbenjaggedben Solar Expert Posts: 230 ✭✭
    Re: Wiring solar panel on the roof while waiting for inverter delivery

    When was the last time you ordered a GT inverter? And do you realize that typically the disconnect comes with the inverter these days?

    The bottom line is that he needs to avoid energizing his conductors until after they are terminated and he may not be able to do that, or may not wish to do that, until after his inverter is delivered.
  • vtmapsvtmaps Solar Expert Posts: 3,739 ✭✭✭✭
    Re: Wiring solar panel on the roof while waiting for inverter delivery
    jaggedben wrote: »
    When was the last time you ordered a GT inverter? And do you realize that typically the disconnect comes with the inverter these days?

    The bottom line is that he needs to avoid energizing his conductors until after they are terminated and he may not be able to do that, or may not wish to do that, until after his inverter is delivered.

    I believe that NEC requires a disconnect outside. Its also good to have a disconnect indoors with (or built into) the inverter. I don't see any reason the OP can't wire up everything to the inverter, as long as he has his external disconnect in place.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Wiring solar panel on the roof while waiting for inverter delivery

    The argument is fatuous because the wires will be just as energized when the inverter does arrive for connection as they are now, no matter where the disconnect is. You have to hook them up sometime.

    Anyone who is that concerned about it should leave the connections between two panels in each and every string of the array unplugged: absolutely zero Voltage potential from either positive or negative in respect to each other or to ground. Then when the disconnect is finally in place all wires are connected, re-joining the panels last, and the switch is thrown.

    But it is not the big safety hazard some would make it out to be.

    vtMaps; sometimes it is the local AHJ that wants the disconnect outside and accessible so that it can be switched off in case of fire. This may mean locating the inverter outside (bad idea in most climates) or having a second external disconnect. If the inverter's connections do not include the mandated DC GFI then that will also require a second disconnect in the form of the breakers for that.

    As always, no one has to heed my advice; it's not my money you're spending.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Wiring solar panel on the roof while waiting for inverter delivery
    vtmaps wrote: »
    I believe that NEC requires a disconnect outside. Its also good to have a disconnect indoors with (or built into) the inverter. I don't see any reason the OP can't wire up everything to the inverter, as long as he has his external disconnect in place.

    --vtMaps
    The NEC does not require a DC disconnect external to the inverter. It requires a DC disco, but (for example), the DC disco integral to an SMA Sunny Boy will suffice. Some AHJ's may not agree, but in those cases it's their extension of the NEC, not the NEC itself.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Wiring solar panel on the roof while waiting for inverter delivery

    You guys may be saying the same thing. I would advise leaving one of the home runs for each string disconnected from the array until the combiner box(es) and/or external (as in not integral to the inverter) DC disco, if either/both are present, are wired up so that you are not working hot, but after that, connect them. If the inverter has the home runs going directly into it, leave the home runs disconnected until the inverter is ready to rock. You should never be working on uninsulated bare ends if they are energized.
  • jaggedbenjaggedben Solar Expert Posts: 230 ✭✭
    Re: Wiring solar panel on the roof while waiting for inverter delivery
    But it is not the big safety hazard some would make it out to be.

    It is certainly a big enough safety risk that the OP, who does not necessarily sound that experienced, should be given advice on how to deal with it. I mean, if he had to ask the question...
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