Another Grounding Question

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  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Another Grounding Question
    Fatawan wrote: »
    My main and subpanel(400A service) is on the basement wall right behind the meter in that picture. I still ponder where to do the connection. Since I will have 4 branch circuits, each will will need a 15A breaker somewhere along the line, and the utility requires a disconnect that is outdoors and not fused. Do I get a disconnect that has 4 inputs and go from there to the basement subpanel, or subpanel outside, then to disconnect, or ??? I guess I have to inquire about how the various setups would affect the Envoy communications for monitoring as well.

    I want to reassure you all that I am doing this all as a precursor to my actual electrician handling the wiring. First time solar install for him, so he too will appreciate all these little bits of info.

    Here's how I'd do it...


    At the array end:

    Outdoor breaker box (sub-panel) at the array with the 4 (?? Is that right? You're using 4 Enphase strings and 4 AC pigtails?) 15a DP breakers in it (8 (??) breaker slots used).

    Run the pigtails from the Enphase strings into that sub-panel. (It serves as the "junction box" described in the Enphase instructions.)

    Connect the Enphase pigtails to the breakers and the neutral bus bar. (The pigtails don't have a green EGC, so they don't connect to the ground bus bar.)

    Do not bond the neutral bus bar to ground in that sub-panel. If it's already bonded - isolate it.

    Drive a ground rod and run a continuous GEC (bare #6) through the PV frames/racking to that rod. Also run another continuous GEC through the Enphase ground lugs to the ground rod.

    (The question of course is: Can you just use one GEC for both? According to Wiles, you can.

    But I wouldn't. The PV is DC only. The Enphase...well...who really knows. It IS a device with AC in it somewhere, so I'd just prefer to treat its chassis as something that could possibly become hot with AC - in which case I'd prefer it have its own GEC rather than sharing with the PV. That's just my own personal kink though and no doubt I'm just being overly cautious.)

    OPTIONAL (I think...): Also run another #6 bare from the ground bus bar in the sub-panel, to the array ground rod. I would. This would also fulfill Wiles' description (in that link I posted) of tying the AC EGC, to the Enphase DC GEC. (The part where he describes connecting a bare #10 EGC from the j-box EGC to the #6 GEC.)


    At the house:

    Mount an outdoor non-fused 240v disconnect of appropriate size. Run a conduit (or whatever) from that disconnect to the main breaker panel.


    Tying it all together:

    Dig a trench, run a conduit from the disconnect at the house, to the array sub-panel. Pull in 4 appropriately sized wires - two hots, one neutral and one green EGC ground.

    Also lay a #6 bare solid wire in the trench next to the conduit.


    At the array end, connect the 4 wires to the appropriate bus bars in the sub-panel. The building EGC system *ends* there, because the Enphase system doesn't have an AC EGC conductor in its pig tails - unless you add the bare #6 from the sub-panel to the ground rod, in which case the building EGC is carried through to the last Enphase chassis at the end of the Enphase chassis GEC. That's how you provide the AC EGC to the doofy Enphase inverters...

    Connect the bare ground wire in the trench to the array ground rod.

    OPTIONAL: Install lighting arrestors. I would.


    At the house end, connect the two hot wires from the trench conduit to one side of the disconnect. Bond the green EGC to the disconnect box. Pass the neutral through to the main panel.

    In the main panel, install an appropriately sized breaker, and land the two hots from the other side of the disconnect in that breaker. Connect the neutral to the neutral bus bar, and the green EGC ground to the ground bus bar.

    Connect the bare #6 from the trench to the house ground rod.


    Call for inspection. If it passes, fill in the trench.



    Now, you don't have to do it exactly like that. You could run enough hot wires in the trench for all the Enphase hots, and just use a junction box to connect them to the Enphase pigtails - but you'll still have to combine them somewhere before the disconnect. If you gotta use a sub-panel anyway, it's cleaner to put it at the array end. It also gives you a means of disconnect at the array end, which is a good thing.


    Another thing to consider is: What are the utility company's requirements? Do they require a second meter socket for net metering? If so, then you have to add that in between the disconnect and the main panel.


    A picky inspector might require another breaker in the sub-panel at the array, and land the two hot wires coming from the house into that so it serves as a main disconnect for the sub-panel. It wouldn't be required if the sub-panel was a load only, since there is a breaker in the main panel that feeds it - but since it is a supply panel...inspector's choice I think. I wouldn't put it in unless he asked for it - but I would use a sub-panel with a few extra breaker slots just in case. The extra slots also allow the sub-panel to be used as a normal sub-panel to supply a few circuits for a convenience outlet or a sprinkler timer or outdoor lights or whatever.
  • FatawanFatawan Solar Expert Posts: 71 ✭✭✭
    Re: Another Grounding Question

    dwh:

    Thanks so much. That is perfect! That took a great deal of effort and I appreciate it(and so will my electrician, and the inspector, and .........)
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Another Grounding Question

    let us know what your electrician thinks and how it goes on inspection too.
    good luck.:D
  • FatawanFatawan Solar Expert Posts: 71 ✭✭✭
    Re: Another Grounding Question

    .....and 3 months later, I am close to inspection! Electrician will be here in next few days. I have followed dwh's excellent plan. The panels are in, micorinverters mounted and connected, conduit run in 18" trench along with a bare #6 wire in the same trench, the pigtails are hanging there waiting for the subpanel(mounting post for subpanel installed). I have run #6 bare copper to each inverter. My question is more about technique. I had to do the ground in two separate wires because #6 copper wire sucks to mess with and I wasn't able to feed it through all the mounts and such in one continuous piece(note to self--do it before mounting panels next time--DOH!). So i have two tails of #6 hanging from the low edge of the array, about 6' from the ground rod, 2' off the ground. I will also have a run of 12 AWG wire from the frames of the panels(Sanyo install instructions said to use it, and inspector said "follow install instructions"). I will also run a piece of #6 for the railings. So, do I hook all these wires up to separate lugs at the rod? Can I gang up wires on one lug? Do I need to put them in conduit from the spot where they leave the array to where they connect to the rod or can I bury them in the earth and over to the ground rod? Essentially, how to get all the dangling ground wires over to the rod in a code=friendly manner :D

    Thanks for helping me to this light-at-end-of-tunnel spot!
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Another Grounding Question
    Fatawan wrote: »
    .....and 3 months later, I am close to inspection!

    Nice!

    Electrician will be here in next few days. I have followed dwh's excellent plan.

    I'm interested in his opinion of the layout.


    The panels are in, micorinverters mounted and connected, conduit run in 18" trench along with a bare #6 wire in the same trench, the pigtails are hanging there waiting for the subpanel(mounting post for subpanel installed). I have run #6 bare copper to each inverter. My question is more about technique. I had to do the ground in two separate wires because #6 copper wire sucks to mess with and I wasn't able to feed it through all the mounts and such in one continuous piece(note to self--do it before mounting panels next time--DOH!). So i have two tails of #6 hanging from the low edge of the array, about 6' from the ground rod, 2' off the ground. I will also have a run of 12 AWG wire from the frames of the panels(Sanyo install instructions said to use it, and inspector said "follow install instructions"). I will also run a piece of #6 for the railings. So, do I hook all these wires up to separate lugs at the rod? Can I gang up wires on one lug? Do I need to put them in conduit from the spot where they leave the array to where they connect to the rod or can I bury them in the earth and over to the ground rod? Essentially, how to get all the dangling ground wires over to the rod in a code=friendly manner :D

    Thanks for helping me to this light-at-end-of-tunnel spot!

    First of all, make sure that the ground wires are secured...i.e., strapped to something. I don't like it when ground wires are left hanging in some state that can allow them to be disturbed.

    For instance, I've seen them ripped loose from the ground rod when some gardener got his lawnmower caught on it and just yanked back and ripped it loose. I've also seen them ripped loose when someone used a hanging loop as a handy stepladder.


    Next, use a separate ground clamp for each ground wire. Don't combine them.

    This is my favorite style of ground clamp:

    Ground-clamp.jpg

    As you can see, the lower jaw has teeth on the outside. In the pic, it's configured to clamp to a pipe, but you can flip the lower jaw and it works on a ground rod as well.

    It also has a small clamp at the top, beside the lug where the wire goes through. That's in case the local authority requires the ground to be "armored". If they do, then the wire goes through the lug and the big screw holds it, and the armor gets clamped as well.


    In some areas of Los Angeles, we are required to run a continuous unbroken *armored* ground wire, from the panel, to a water pipe and then to a ground rod. In that situation, we use two of these ground clamps, back to back at the water pipe. We take the armor off the wire from the water pipe to the ground rod, run the wire throught the back to back clamps and then slide the armor back on. That way both pieces of armor are clamped at both ends.

    Whether or nor your locale requires the ground be armored or in conduit is something that your local electrician can answer.

    If you don't need armor, then you can get the same style but without the extra clamp for the armor.

    I'm also a fanatic, so I leave an extra inch of wire. That way, after it goes through the lug and the screw clamps down on it, I can then bend that extra inch back over the clamp which is just a little extra insurance that it won't get pulled out. (Inspectors love details like that as well.)




    I'm not sure what the #12 is for. Sanyo install says use it you say? For what? PV frame ground?

    Well, if you've run #6 through ground lugs on the PV frames, then that is *more* than the #12 Sanyo recommends, so I don't see needing a #12 as well.

    But if you used #12 for the PV frame grounds *instead* of #6...well I guess it would be up to your inspector if he passes that.


    Looking forward to hearing the outcome.

    And where are the pics? (If there are no pics, it didn't happen! :D )
  • FatawanFatawan Solar Expert Posts: 71 ✭✭✭
    Re: Another Grounding Question
    dwh wrote: »
    Nice!




    I'm interested in his opinion of the layout.

    He opted not to connect the subpanel at the array to the array ground rod. He said if he did do that, he would have to pull a larger wire in the conduit and add a main breaker in the subpanel. Otherwise, he agreed with and implemented everything you said.




    First of all, make sure that the ground wires are secured...i.e., strapped to something. I don't like it when ground wires are left hanging in some state that can allow them to be disturbed.

    For instance, I've seen them ripped loose from the ground rod when some gardener got his lawnmower caught on it and just yanked back and ripped it loose. I've also seen them ripped loose when someone used a hanging loop as a handy stepladder.


    Next, use a separate ground clamp for each ground wire. Don't combine them.


    I'm also a fanatic, so I leave an extra inch of wire. That way, after it goes through the lug and the screw clamps down on it, I can then bend that extra inch back over the clamp which is just a little extra insurance that it won't get pulled out. (Inspectors love details like that as well.)

    Done



    I'm not sure what the #12 is for. Sanyo install says use it you say? For what? PV frame ground?

    Yes, Sanyo instructions for frame ground.
    Looking forward to hearing the outcome.

    And where are the pics? (If there are no pics, it didn't happen! :D )

    Pics to follow.

    Outcome? Such a letdown for an ending! I bet the inspector was here for one minute total. He looked at the subpanel, looked at the disconnect, signed the OK, and was gone. That's it. I am sure glad you folks helped me with how to do it correctly.

    Thanks again.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Another Grounding Question
    Fatawan wrote: »

    Outcome? Such a letdown for an ending! I bet the inspector was here for one minute total. He looked at the subpanel, looked at the disconnect, signed the OK, and was gone. That's it. I am sure glad you folks helped me with how to do it correctly.

    Thanks again.
    The level of inspection you get depends on where you are. Here in Austin the inspector looks at everything and may fail you for a drooping wire, but when I had an inspection of a system out at a lake house, the utility guy showed up, put a meter on the system side of the disconnect, threw the switch and saw that the anti-islanding worked, and signed off on it. Thirty seconds, max, and he was down the road.
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Another Grounding Question
    Fatawan wrote: »
    He opted not to connect the subpanel at the array to the array ground rod. He said if he did do that, he would have to pull a larger wire in the conduit and add a main breaker in the subpanel. Otherwise, he agreed with and implemented everything you said.

    So he's using the house rod for the AC system equipment ground, and the array rod for the PV frames and racking. That works too.

    Outcome? Such a letdown for an ending! I bet the inspector was here for one minute total. He looked at the subpanel, looked at the disconnect, signed the OK, and was gone. That's it. I am sure glad you folks helped me with how to do it correctly.

    Thanks again.

    Yea, often inspectors have inspected many jobs from a particular electrician, so they know they can trust his work to be done right.

    Congrats on passing! Good job!
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