another grounding question

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hillbilly
hillbilly Solar Expert Posts: 334 ✭✭
in Off Grid Solar & Battery Systems #1
I'm in the process of adding some PV panels to my current system, and will need to utilize a second CC. I've been stumbling around with some of the installation specifics, notably GFP. Right now my system has a 63amp ground fault protection breaker installed. I get confused about how grounding would work if I add a second array and charge controller in the mix. As I understand it, the neutral to ground bond is accomplished via the GFP breaker, without it I would make a connecting wire run between the ground bus and neutral bus directly.

I'm having a hard time visualizing how a second CC would work relative to GFP; on the one hand it seems to me like it would need it's own GFP breaker, while on the other hand that seems like it would create a potential ground loop? I'll freely admit to being easily confused when it comes to grounding issues, so I did some searching here and it looks like there is some controversy regarding DC-GFP in off grid systems. Now I'm thinking that it might just be simpler (and possibly more effective) to just remove the GFP breaker I have now and go with a solid #6 wire to connect the neutral and ground buss bars?

I am curious for any thoughts or opinions on what others have done or would do in this case. I see three main options:
A) one GFP breaker only
B) Two GFP breakers, one for each CC
C) No GFP, tie neutral and ground together in the panel with solid wire connection.

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

    You're not alone in your confusion. This is one of the most confusing things that the NEC has come up with so far.

    My understanding (possibly wrong) is that each CC has its own array and GFDI. The negatives are no longer bonded to ground except through a small resistor. When the breaker detects current potential between ground and neutral (indicating positive is shorted to ground) it trips and breaks the positive line, leaving the negative connected to ground via the resistor (to eliminate potential negative Voltage sourcing).

    Outback's version: http://www.outbackpower.com/docman/1401103030655Ground_Fault_Detector_Interrupter_REV_A.pdf

    That show interrupting the positive from CC to battery. Midnite's shows interrupting positive from panels to CC. I'm still not clear which is right.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,443 admin
    #3
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    Re: another grounding question

    There is a thread over at the Midnite forum were I and a few others discussed the DC GFP system/requirements.

    Ground Fault Protection

    Short answer, I would disable/ignore the DC GFP system and tie a solid ground between DC Return and Earth/Frame ground (the ground bond has to be heavy enough wire to carry the maximum fault current you would expect--wire may need to be larger than 6 awg for large systems).

    Longer answer, each manufacturer's system and each installation is different--You will need to review the manuals and your system to decide what you want to do and how to accomplish it.

    Also, if yo have a building inspector involved, you may need to discuss your plans with them before you do a bunch of work. And I am not sure that the average inspector would have a clue/opinion about DC GFP protection unless you educate them.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • hillbilly
    hillbilly Solar Expert Posts: 334 ✭✭
    #4
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    Re: another grounding question

    Thanks for the replies:
    'Coot, I have an E-panel from Midnite Solar and it has the GFP wired between the PV IN and the CC (the actual wire path is PV+ --> 50amp breaker --->GFP--->CC--->50amp breaker--->Batt+), which is the same configuration that was illustrated in my user manual with the MX 60.

    Bill, it was that thread on the Midnite board that I found while searching for some further enlightenment on how to safely wire 2 parallel CC's. A bit of that went well over my head, but it did make me really think what exactly GFP does here (the good and the bad). As far as an inspection, this is an addition that I'm doing on my own and wont be inspected. I'm all for following code, and don't mind a bit of extra expense and/or work if need be, but my main concern of course is to make the installation as safe as possible. You made some pretty convincing arguments against using GFP at all, and I was interested to hear more opinions on these issues. I also wasn't sure if hooking up a second CC without GFP would create further issues or not. At this point, tbh, I'm leaning towards removing the GFP breaker that I have and just going with a normal neutral to ground connection.

    Thanks again
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