Help with inverter grounding

rgk1
rgk1 Solar Expert Posts: 135 ✭✭✭
in Advanced Solar Electric Technical Forum #1
I am new to building a solar project as well as posting on any kind of forum, so be patient with me. First some detail of my first build which is off grid. I have a SureSine 300 inverter, and a Sunsaver MPPT charge controller all wired to a Midnite Solar DC disconnect panel which has breakers for PV disconnect and DC ground fault breakers. My inverter is wired as the manufacturer recommends, except that instead of battery connections going directly to the battery and ground wire going to grounding rod, they all make those connections inside the DC disconnect panel. My concern is that the ground wire to the inverter (on the DC side) also has the wire from the AC side connected to it to make one of the isolated AC outputs the neutral. It would seem to me that this puts AC neutral sharing the same ground buss as the DC. I can touch the metal chassis of the disconnect box...no shock. But, if you test for voltage between the "hot" wire on the AC side of the inverter and the metal chassis of the DC disconnect I get 113 volts. Is this a normal condition, same as checking for voltage between the hot side of a home outlet with grid power and a homes ground rod, or is something terribly wrong? I have considered a separate ground rod for DC and AC, but that appears to bring up a whole new set of issues. Any help is greatly appreciated.
4-Risen 320 watt in series/parallel, 8-215ah 6 volt GC2 batteries in series, Exeltech 1100 watt/48 volt inverter, Tristar 45 MPPT controller.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Help with inverter grounding

    Doesn't sound like anything wrong to me.

    Normally on the AC side of things the AC ground is connected to Earth, and the AC neutral is bonded to the ground at one point only. This is standard AC wiring. You will read something close to 120 VAC between AC hot and any safety ground point. It will vary due to resistance on the grounding side.

    You have a true sine wave inverter, so it is safe to connect the DC ground and AC ground. If it were an MSW-type inverter, it would have burnt up by now. On those the AC neutral must not be bonded to ground.

    As long as you don't get a Voltage reading between AC neutral and AC ground, you're fine.
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #3
    Re: Help with inverter grounding

    You should be able to put a meter probe on the hot side of the inverter, and the other probe on the grounded fuse box and see 120 vac. That would be normal. The big issue is (as we have discussed off line) is the grounding configuration of the entire system. I believe the proper installation is to have the battery/PV ground and the inverter ground share the same ground point. Multiple paths to ground is what causes problems. I think we have discussed this elsewhere on this forum, and I'm sure that BB will chime in with the definitive answer.

    Tony
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  • rgk1
    rgk1 Solar Expert Posts: 135 ✭✭✭
    #4
    Re: Help with inverter grounding

    Thats a funny thing I don't understand about the SureSine, there is no AC ground. Only hot and neutral output terminals. When checking with a voltmeter, I can only find voltage between the hot output terminal and the neutral terminal on the AC side or between hot on the AC side and anywhere there is a ground wire on the DC side..including the negative wires on the charge controller as they ultimately make a connection to the ground buss via the DC ground fault breaker.
    4-Risen 320 watt in series/parallel, 8-215ah 6 volt GC2 batteries in series, Exeltech 1100 watt/48 volt inverter, Tristar 45 MPPT controller.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: Help with inverter grounding

    From the install manual:

    "NOTE: The AC output is isolated, therefore AC line and neutral are interchangeable. Use UL Listed 12AWG (4 mm2) black wire for AC Line and UL Listed 12AWG (4 mm2) white wire for AC Neutral. The earth grounded leg defines AC Neutral."

    So you can ground either side and make it neutral. (In the case of the 220 V model neither side is grounded of course.)
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  • rgk1
    rgk1 Solar Expert Posts: 135 ✭✭✭
    #6
    Re: Help with inverter grounding

    That's the way i have it. Black wire for hot, white for neutral with the addition of another wire connecting neutral to ground. It was a bit unsettling to have an AC neutral in my DC ground system, but it sounds like all is ok. Thank both of you for your help.
    4-Risen 320 watt in series/parallel, 8-215ah 6 volt GC2 batteries in series, Exeltech 1100 watt/48 volt inverter, Tristar 45 MPPT controller.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #7
    Re: Help with inverter grounding
    rgk1 wrote: »
    It was a bit unsettling to have an AC neutral in my DC ground system.

    You've done it right. I have two of them (SureSine 300), one in continuous operation 24/7/365, the other only as needed for dedicated loads, a number of times each day, for 3 years now. Awesome inverters, wish they had a bigger one.
    Don't so much think of having "an AC neutral in your DC ground system", rather just think of it as a common ground for both your AC and DC, which eliminates any voltage differences between the two grounds, that could exist if they were grounded separately, especially during lightening storms.
    Only fault I find with the SureSine 300 is that they shut down on over-voltage at 15 volts, which isn't all that hard to attain on a very cold but sunny winter day, especially if doing an EQ on the batteries. Would be awesome if they could handle 16 volts before shutdown.
    Still, I love them! Extremely well built and well behaved :-)
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  • Eric L
    Eric L Solar Expert Posts: 262 ✭✭
    #8
    Re: Help with inverter grounding

    I'd like to piggyback a short question on this thread. I also have the Suresine 300, and have wired it per instructions with AC neutral sharing the DC system ground. However, I don't go through a distribution panel, but rather have wired the inverter directly to a GFCI receptacle. That receptacle also has its own grounding terminal.

    Should I run a wire from that grounding terminal on the GFCI to the common system ground?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #9
    Re: Help with inverter grounding
    Eric L wrote: »
    I'd like to piggyback a short question on this thread. I also have the Suresine 300, and have wired it per instructions with AC neutral sharing the DC system ground. However, I don't go through a distribution panel, but rather have wired the inverter directly to a GFCI receptacle. That receptacle also has its own grounding terminal.

    Should I run a wire from that grounding terminal on the GFCI to the common system ground?

    Eric, is this in your RV? If so, ditch the GFCI because there is no Earth ground to connect to. The GFCI works by "measuring" (loosely speaking) the current going in and out Hot and Neutral. If it detects a difference of sufficient magnitude indicating power is flowing through some alternate path it shuts off power. Your neutral, ground, and DC (-) are already connected.


    GFCI's are often more trouble than they're worth, in my opinion. Remember for decades we had AC outlets that had NO ground terminal. Most of the time it was no problem. Arc-fault breakers are another case of "make people spend money for a false sense of security". And don't get me started on DC-side GF circuits. :grr

    Someone will no doubt disagree with me on one or all of these points.
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  • Eric L
    Eric L Solar Expert Posts: 262 ✭✭
    #10
    Re: Help with inverter grounding

    Coot,

    It's not an RV; the outlet is in my garage and I have an earth ground for my solar system. I used this GFCI receptacle only because it was one of the 'approved' outlets listed in the Suresine user's manual (actually it's the successor model to one of the approved receptacles).

    I haven't connected that ground wire on the outlet, but I'm wondering if it would be better if I did.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #11
    Re: Help with inverter grounding

    Eric;

    In that case connect up the ground. It will work as a safety measure where there is an actual Earth ground.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,631 admin
    #12
    Re: Help with inverter grounding

    The GFI outlet should work OK (as a safety device) without a Green Wire Ground connected...

    However, this will "float" any three wire AC appliances (not considered a good thing to do) and the push to test GFI button may not work (some use the green wire to run the test leakage current).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Eric L
    Eric L Solar Expert Posts: 262 ✭✭
    #13
    Re: Help with inverter grounding

    O.k., I connected it. Thanks guys.
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  • System2
    System2 Posts: 6,290 admin
    #14
    Re: Help with inverter grounding

    Now I'm using the SureSine 300 in my RV. Or should say I want to. I just bought it and am in the process of connecting it up.

    Again, considering only the black (hot side) and the white (neutral side) connected to the inverter (ac side). Operating manual shows you connecting the white side to earth ground. Well for my RV that would be the chassis. As well the neg side of the battery is also connected to the chassis.

    I’m just uncomfortable connecting things this way, but is this right?
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