Another grounding question

elesaver
elesaver Solar Expert Posts: 185 ✭✭
in Solar Beginners Corner #1
Please excuse the need for another grounding question. I have re-read some info on this issue that I had saved but I'm still not clear.

Here's the scenerio: I am switching to an Outback VFX3524 inverter. The former inverter (Cotek SK1500_) was not hardwired into the system but instead, utilized built-in outlets. This inverter was earth grounded. It has worked wonderfully well but it's time to upgrade. (Remember that we all know solar is addicting. But, I digress.)

The Cotek 1500 goes through a Midnite Solar mini dc disconnect. This time, I am going to wire the Outback inverter and an Outback psx-240 into an electric panel. This panel is not a sub-panel or connected in any way to the main service panel. It's as though it is a new service like at a cabin or something. I am going to move the circuit breakers that I want to use with solar from the main service panel over to the new panel. The new panel is 100 amp. so I won't be moving many.

The Cotek 1500 was earth-grounded at the lug on the case near the battery connections. The Outback also has a lug for grounding at the battery connections. I am going to move the Cotek battery connections and earth ground over to the Outback so nothing really has changed at this point except the inverter from the Cotek to the Outback.

Now, the Outback has to be hard-wired. There is AC hot, AC neutral, and a chasis ground. I will run the AC hot to the proper 25A circuit breaker and the neutral to the neutral busbar inside the casing for the transformer. The two wires exiting the transformer circuit breakers will carry 240A and I will attach them to the main shut off circuit breakers in the new panel.

So, here's the question: I would think the panel has to be earth grounded which I can do. But, meanwhile, I already will have an earth ground at the battery connections of the Outback 3524. All info I have read says to have only one neutral-ground connection at a time so which one do I ground...the lug by the battery terminals or run a ground from the Outback chasis ground to the panel ground bar and then to earth ground?

I hope I've explained the conundrum. Thanks for help. I will happily give more info if this is not clear. And, if the wiring plan that I am considering is not correct, of course I would need to know that, too.
1st system:  24Vsystem with 8 X 300W panels, Midnite Solar combiner box, Midnite Solar mini-dc disconnect, Midnite Solar Classic 150, Outback VFX 3524 with mate, 2 X 12V  fforklift batteries in series 938 aH,  (Outback PSX transformer, Honda EU3000is...not currently hooked up but available if/when needed)

2nd system:  24V system with 4 X 310W panels, Midnite Solar combiner box, Midnite Solar mini-dc disconnect, Midnite Solar Classic 200, Cotek 1500W pure sine inverter, Trojan 125 batteries (8 available but "currently" using 4)

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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Another grounding question

    DC side of the inverter has its negative grounded.
    AC side of the inverter has its neutral grounded.
    Case of inverter is grounded.

    Grounding the inverter case or the DC negative does not create the neutral-ground bond on the AC side.

    Only the AC hot needs breakers, so the neutral and ground wires on AC OUT can be run to the new panel and an N-G bond made there just as you normally would for a service box. Then the ground bus bar is connecting to the grounding rod, and the DC negative and inverter case are also connected to it.

    Simple enough?
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  • elesaver
    elesaver Solar Expert Posts: 185 ✭✭
    #3
    Re: Another grounding question

    It's only simple because you have explained it. :-) Thank you. The fog has lifted.
    1st system:  24Vsystem with 8 X 300W panels, Midnite Solar combiner box, Midnite Solar mini-dc disconnect, Midnite Solar Classic 150, Outback VFX 3524 with mate, 2 X 12V  fforklift batteries in series 938 aH,  (Outback PSX transformer, Honda EU3000is...not currently hooked up but available if/when needed)

    2nd system:  24V system with 4 X 310W panels, Midnite Solar combiner box, Midnite Solar mini-dc disconnect, Midnite Solar Classic 200, Cotek 1500W pure sine inverter, Trojan 125 batteries (8 available but "currently" using 4)

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  • elesaver
    elesaver Solar Expert Posts: 185 ✭✭
    #4
    Re: Another grounding question

    OK, I spoke too quickly. My brain was warm and the temps cool, so the fog is returning.

    Here's the problem in my mind: the VFX is connected to the PSX-240 which is connected to the electric panel. So far, so good. The transformer casing has a ground lug so I will connect that to the earth ground. The two wires from the transformer are both 120VAC so they would be connected to the two main circuit breakers in the panel allowing for the 240. Fog has set in for this discovery: Shouldn't there also be a neutral somewhere to connect to the panel? Any help for "fog elimination" would be greatly appreciated, as always.
    1st system:  24Vsystem with 8 X 300W panels, Midnite Solar combiner box, Midnite Solar mini-dc disconnect, Midnite Solar Classic 150, Outback VFX 3524 with mate, 2 X 12V  fforklift batteries in series 938 aH,  (Outback PSX transformer, Honda EU3000is...not currently hooked up but available if/when needed)

    2nd system:  24V system with 4 X 310W panels, Midnite Solar combiner box, Midnite Solar mini-dc disconnect, Midnite Solar Classic 200, Cotek 1500W pure sine inverter, Trojan 125 batteries (8 available but "currently" using 4)

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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: Another grounding question

    Yep: there's a neutral all right.

    Basic autotransformer wiring: two identical sides; black & white for one, red & white for the other. Feed 120 VAC to black & white, you get a mirror image on red & white. Connect two white wires together and the two 120 VAC sides 'stack' to form 240 VAC. Guess where the neutral is? Center of the transformer: the two white wires that are connected together.
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  • elesaver
    elesaver Solar Expert Posts: 185 ✭✭
    #6
    Re: Another grounding question
    Cariboocoot wrote: »
    Yep: there's a neutral all right.

    Basic autotransformer wiring: two identical sides; black & white for one, red & white for the other. Feed 120 VAC to black & white, you get a mirror image on red & white. Connect two white wires together and the two 120 VAC sides 'stack' to form 240 VAC. Guess where the neutral is? Center of the transformer: the two white wires that are connected together.

    OK, I'm with you so far...but I can't go any further on my own. I see within the psx-240 case that there are two neutrals attached to the neutral bus bar within the case. Are you saying that's all the neutral that is needed...nothing to go into the electric panel itself? I am to just attach the two 120VAC wires exiting the transformer to the main breakers and it's good to go...except for the ground, of course which we've already discussed.
    1st system:  24Vsystem with 8 X 300W panels, Midnite Solar combiner box, Midnite Solar mini-dc disconnect, Midnite Solar Classic 150, Outback VFX 3524 with mate, 2 X 12V  fforklift batteries in series 938 aH,  (Outback PSX transformer, Honda EU3000is...not currently hooked up but available if/when needed)

    2nd system:  24V system with 4 X 310W panels, Midnite Solar combiner box, Midnite Solar mini-dc disconnect, Midnite Solar Classic 200, Cotek 1500W pure sine inverter, Trojan 125 batteries (8 available but "currently" using 4)

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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
    Re: Another grounding question
    elesaver wrote: »
    OK, I'm with you so far...but I can't go any further on my own. I see within the psx-240 case that there are two neutrals attached to the neutral bus bar within the case. Are you saying that's all the neutral that is needed...nothing to go into the electric panel itself? I am to just attach the two 120VAC wires exiting the transformer to the main breakers and it's good to go...except for the ground, of course which we've already discussed.

    No, you'd run a wire from that transformer neutral connection into the electrical panel for the neutral line connections there. Otherwise none of the 120 VAC circuits would work properly owing to a lack of neutral.
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  • elesaver
    elesaver Solar Expert Posts: 185 ✭✭
    #8
    Re: Another grounding question

    OK. Now, once again, the fog is lifting. Temporarily again? I hope not. You have served me well, Cariboocoot. Thank you for your patience. I'm actually rather pleased that I knew there should be a neutral in that electric panel! One of these days, I'm going to PM you with some info. You may get a kick out of it.

    Anyway, a HUGE thanks for making this clear.
    1st system:  24Vsystem with 8 X 300W panels, Midnite Solar combiner box, Midnite Solar mini-dc disconnect, Midnite Solar Classic 150, Outback VFX 3524 with mate, 2 X 12V  fforklift batteries in series 938 aH,  (Outback PSX transformer, Honda EU3000is...not currently hooked up but available if/when needed)

    2nd system:  24V system with 4 X 310W panels, Midnite Solar combiner box, Midnite Solar mini-dc disconnect, Midnite Solar Classic 200, Cotek 1500W pure sine inverter, Trojan 125 batteries (8 available but "currently" using 4)

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  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    #9
    Re: Another grounding question

    Depending on how you do it you sometimes end up with an AC earth bus and a dc earth bus. The NEC provides 3 different ways you can resolve this.

    a) two earth stakes
    b) one stake, with two EGCs.
    c) dc earth linked through the AC earth bus.

    see article 690.47, which is summarised here:

    Grounding and Bonding PV Systems
    http://solpowerpeople.com/wp-content/uploads/2012/08/Grounding-and-bonding-PPT-copy.pdf

    And if you want to read the gory details see page 633:
    https://archive.org/details/nfpa.nec.2014

    All 910 pages of it is now creative commons. The whole of article 690 relates to PV systems and is interesting reading.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


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  • elesaver
    elesaver Solar Expert Posts: 185 ✭✭
    #10
    Re: Another grounding question

    Thanks for the links, zoneblue. I will read these. It'll be slow...but sure!
    1st system:  24Vsystem with 8 X 300W panels, Midnite Solar combiner box, Midnite Solar mini-dc disconnect, Midnite Solar Classic 150, Outback VFX 3524 with mate, 2 X 12V  fforklift batteries in series 938 aH,  (Outback PSX transformer, Honda EU3000is...not currently hooked up but available if/when needed)

    2nd system:  24V system with 4 X 310W panels, Midnite Solar combiner box, Midnite Solar mini-dc disconnect, Midnite Solar Classic 200, Cotek 1500W pure sine inverter, Trojan 125 batteries (8 available but "currently" using 4)

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