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BigFly10's avatar
BigFly10
Explorer
Jul 30, 2013

Another inverter/solar grounding question for the experts

Hello all,

I have just recently installed and wired in my new solar system to my TT which includes the following:
- (4) Deep Cycle / Marine 12V batteries at 120Ah each
- Xantrex Prowatt SW2000 inverter
- GoPower 30A Automatic Transfer Switch
- Sub-panel for breakers to be powered from inverter
- 250W solar panel (plan on adding another 250W panel)
- Tristar MPPT-45 Charge Controller
- Trimetric 2025-RV battery monitor.

I have given it all a fairly thorough testing and it seems to be working pretty well except for one problem. When I run the microwave off the inverter, it "sometimes" trips the GFCI on the Xantrex inverter. When I say sometimes, it seems to be about 50% of the time. I can reset the GFCI and I am away to the races again, but this could be a real pain after awhile.

This got me to thinking about the grounding. I have a decent electrical understanding but not a whole lot of practical experience and am not familiar with the standard wiring practices in an RV. Thinking about grounding gives me a headache. I have done some searching and reading but am still not clear on what is required.

The trailer is basically brand new. Straight from the factory/dealer, the battery had "several" wires connected to the battery - most were from the positive terminal and only one #8 from the battery negative. There is no obvious place I can find where this negative wire is frame grounded I can only "assume" that it runs back to the converter ground terminal strip and that terminal strip is connected to the trailer frame. All these wires "disapper" into the underside of the trailer and it would be very difficult for me to trace exactly where they are going. Rather than changing them, I just left them all connected as they were when wiring in my new components.

When I connected my components, I ran the positive/negative from the battery to the inverter. The inverter has a separate grounding terminal. Then inverter instructions say to connect a cable from the inverter ground terminal to the trailer frame. I did not follow this exactly. From the inverter ground terminal, I joined this ground cable with the ground cable from my Tristar charge controller and from my solar panel, and then ran a bigger ground cable back to my converter which I connected to the grounding strip in the converter panel.

On the A/C side, my inverter comes with two GFCI outlets. I built a cable with a 3-prong plug that I have plugged into the inverter outlet and then ran that cable to my ATS. The other cable to the ATS comes from a 30-amp breaker in the main breaker panel. At the main breaker panel, the cable going to the ATS has positive terminated on the breaker outlet, neutral on the neutral bar, and ground on the ground bar.

The 3 cables at the ATS (2 in and 1 out) are connected to the positive and neutral connections provided in the ATS with the ground cables all connected to the ground terminal strip inside the ATS.

The outlet from the ATS is wired to a small sub-panel with 3 breakers which power my RV outlets and my microwave. The sub-panel has a separate ground and neutral strip which I terminated all of the cables to. This includes the main supply cable from the ATS and the 3 cables supplying the loads in my RV.

So the way I see it, I basically have all of my grounds connected together including my AC and DC grounds. I am assuming they are also connected to the trailer frame somewhere although I am not sure where. I am also wondering if maybe the neutral and ground are bonded together at the inverter although I am not sure how that is wired internally and maybe this is the problem. If the neutral and ground are bonded together at the inverter, could some of the current be returning via the ground instead of the neutral and causing the GFI to sense a fault?

I think I have everything wired okay but, like I said, I am not familiar with RV wiring standards and am wondering if something I have done is causing my GFI problems. Should I be running my inverter ground directly to the trailer frame as per the instructions? Should my AC and DC grounds be kept separate from one another? Is there something else I should be doing?

Thanks for the help everyone.
  • shooted's avatar
    shooted
    Explorer
    Aug 24, 2013
    Herb40 wrote:
    VintageRacer wrote:
    Make sure your sub panel does not have neutral bonded to ground. It must separate neutral and ground, the transfer switch must switch both neutral and hot to the inverter, which must bond neutral and ground. Neutral is always bonded to ground at one point only, and that is the source of the power. Remember that GFCI - ground fault circuit interrupter - is a bit of a misnomer. The device does nothing with ground at all and can be installed in a circuit that does not have ground (such is code-allowed for protecting old 2 conductor wiring in old houses). It does trip if there is any difference between the current flowing in the hot conductor and the current flowing in the neutral conductor. Having neutral bonded in two places can create such a difference.

    Brian

    Brian, my Todd PS250 ATS in our Beaver Monterey is 17 years old. It still works, but the shore power contactor in it looks slightly off-color (burned?) on the outer plastic. I am considering replacing the PS250 with a manual transfer switch. But the manual transfer switches I've found switch only the hot wires, not the neutral. According to what you've written above, it wouldn't be acceptable if I were to simply connect all of the neutrals together (shore, generator, output). What's the deal here? Why does the neutral have to be switched?


    Here is an option.

    Edit, with regards to the neutral, I copied my response from another thread that this question came up on.

    Isolating power sources is not something to be taken lightly. It is not only prudent but also required by code to isolate BOTH the hot and neutral. If done incorrectly there is a health risk.

    NEC 551.33 Alternate Source Restrictions. Transfer equipment, if not integral with the listed power source, shall be installed to ensure that the current-carrying conductors from other sources of ac power and from an outside source are not connected to the vehicle circuit at the same time.

    In this application the neutral would be considered a current-carrying conductor, and in the previous post the neutral from the inverter is tied to the shore power neutral with no means of disconnect.

    NEC 705.20 Disconnecting Means, Sources. Means shall be provided to disconnect all ungrounded conductors of an electric power production source(s) from all other conductors.

    With regards to this topic, the grounded conductor(neutral conductor), is ungrounded.

    Many inverters actually read 60 volts between the neutral and ground. If this neutral is not isolated from the shore power cord, the shore power cord will also have this 60 volts exposed on the plug! Ouch! Here is a final reference explaining this.
  • Herb40's avatar
    Herb40
    Explorer
    Aug 24, 2013
    VintageRacer wrote:
    Make sure your sub panel does not have neutral bonded to ground. It must separate neutral and ground, the transfer switch must switch both neutral and hot to the inverter, which must bond neutral and ground. Neutral is always bonded to ground at one point only, and that is the source of the power. Remember that GFCI - ground fault circuit interrupter - is a bit of a misnomer. The device does nothing with ground at all and can be installed in a circuit that does not have ground (such is code-allowed for protecting old 2 conductor wiring in old houses). It does trip if there is any difference between the current flowing in the hot conductor and the current flowing in the neutral conductor. Having neutral bonded in two places can create such a difference.

    Brian

    Brian, my Todd PS250 ATS in our Beaver Monterey is 17 years old. It still works, but the shore power contactor in it looks slightly off-color (burned?) on the outer plastic. I am considering replacing the PS250 with a manual transfer switch. But the manual transfer switches I've found switch only the hot wires, not the neutral. According to what you've written above, it wouldn't be acceptable if I were to simply connect all of the neutrals together (shore, generator, output). What's the deal here? Why does the neutral have to be switched?
  • BigFly10's avatar
    BigFly10
    Explorer
    Aug 14, 2013
    Well folks, I think I now have the problem "fixed".

    As per 3 tons suggestion, I tied in for the shore power supply to the ATS PRIOR to the main panel. This did not completely fix the problem but seemed to reduce the frequency of the GFI trips from about 20% to about 10%.

    I then "tuned" the system with an extra 25 feet of cable on the power feed line to the microwave outlet.

    After these two changes, I tried the microwave approximately 35 times with no GFI trips. The problem may not be 100% fixed but this is good enough for me.

    I don't really understand it but now that I think about it I have had the GFCI on my house trip on several occasions for reasons I don't understand either. Perhaps, as suggested, the removal of the "circular currents" from the main panel connection in addition to the capacitance from the longer cable creating a "smoothing" effect on the system was enough to make the GFI happy.

    Thanks very much to those that provided assistance and hung with me throughout this thread. This site is amazing.

    Ryan
  • BFL13's avatar
    BFL13
    Explorer II
    Aug 14, 2013
    You spilled something that got on the receptacle front and the MW plug that is conducting for the GFCI. As long as you don't put those two things together you are good.

    Or, you could wash off whatever it is on the cover and the plug. :)
  • pianotuna's avatar
    pianotuna
    Nomad III
    Aug 13, 2013
    Hi BigFly10,

    It doesn't have to the be fridge--it can be any 120 volt load, for example a 100 watt light bulb.

    BigFly10 wrote:
    pianotuna wrote:
    Hi,

    Seeing as the GFI is part of the inverter changing to another would be--hard.

    I've occasional had my inverter fail over when attempting to run the microwave. The work around for me was to place a small load on the inverter to "wake it up". The fridge works well for this at 300 watts.

    It is interesting you say this because, as mentioned in my testing, when I run my fridge in the rear of the TT before the microwave, it doesn't trip the GFI. I usually don't run this fridge off the inverter though and I would prefer not to turn it on each time I want to run the microwave.
  • 3_tons's avatar
    3_tons
    Explorer III
    Aug 13, 2013
    BigFly10 wrote:
    3 tons wrote:
    Upon re-read,

    "The other cable to the ATS comes from a 30-amp breaker in the main breaker panel. At the main breaker panel, the cable going to the ATS has positive terminated on the breaker outlet, neutral on the neutral bar, and ground on the ground bar."


    Since your ATS switch receives it's A/C input from the main panel, your problem may be one of competing 'circular currents' causing the sensitive inverter GFI outlet to trip. Try powering the ATS from ahead of the main panel (where shore power first enters coach), not after (then divide entrance (in parallel) to main panel & ATS), and you should see a difference, problem corrected...

    Best Regards,

    3 tons

    I seriously considered wiring the system as you suggest when I set it up, however, I was concerned about how to limit the incoming current to the allowable 30 amps. If I tied off before the main breaker, then I could potentially be supplying up to 30 amps to the main breaker in addition to whatever the maximum is that could also be going to the ATS or sub-panel. It means that I would have to install an additional current limiting device upstream of where my parallel branch starts. To me it seemed easier just to use one of the empty slots in the main panel and then supply the sub-panel from the main panel.

    Regardless, what you say makes sense and I may end up going this route if nothing else solves the problem. Thank you for the suggestion.


    This (in my view - as wired) is an unnecessary safeguard that is causing your present problem in its entirety (circular currents that your GFI is sensing...), since (if power were to be somehow mismanaged/exceeded by you) the C/G pedestal will trip at 30amps anyway...

    A change will provide the relief you're looking for...As presently wired, a hard-wired inverter will solve the problem as well...
  • time2roll's avatar
    time2roll
    Nomad
    Aug 13, 2013
    I don't think it is a grounding issue but rather some start up imbalance issue. I believe the GFI will trip when current differential between hot/neutral approaches 5 milliamps.

    You might try running your home microwave on the inverter and see what happens.
  • BigFly10's avatar
    BigFly10
    Explorer
    Aug 13, 2013
    pianotuna wrote:
    Hi,

    Seeing as the GFI is part of the inverter changing to another would be--hard.

    I've occasional had my inverter fail over when attempting to run the microwave. The work around for me was to place a small load on the inverter to "wake it up". The fridge works well for this at 300 watts.

    It is interesting you say this because, as mentioned in my testing, when I run my fridge in the rear of the TT before the microwave, it doesn't trip the GFI. I usually don't run this fridge off the inverter though and I would prefer not to turn it on each time I want to run the microwave.
  • BigFly10's avatar
    BigFly10
    Explorer
    Aug 13, 2013
    MEXICOWANDERER wrote:
    "Actually, Ground Fault is correct terminology. It means that there is a fault to TO ground, ie a fault between one of the current carrying wires and ground, allowing some current to flow directly to ground rather than through the neutral."


    GCFI's are S-E-N-S-I-T-I-V-E

    If more than a PREDETERMINED amount of current chooses to go to earth rather than negative it will fault the device. It absolutely does not have to be even close to 1/100th the amount of current going to neutral. This is a THRESHOLD grade problem and if you allow it to it will drive you nuts - for no reason IMHO.

    A different BRAND of GCFI can cure this problem or "tuning" the feeder circuit like you are doing.


    Thank you. It is driving me nuts. I will continue trying to "tune" the system. Since it doesn't trip with the extension cord I may just simply "extend" the cable supplying the microwave outlet and see if that fixes the problem. I may also try replacing the outlet at the microwave with something different and see it that helps too. I will inspect the wiring in the ATS to confirm it looks okay too, but I am starting to seriously doubt that is where the problem is.
  • BigFly10's avatar
    BigFly10
    Explorer
    Aug 13, 2013
    shooted wrote:
    Is there no way of distinguishing between a ground fault or overload condition on this inverter? An overload condition is starting to make more sense than a ground fault condition
    Edit
    I now see the inverter has a standard gfci output, which when trips should easily be distinguishable from O/L condition.
    On a different note, the inverter is limited to 15 amps, not 20 from my reading of the manual.
    At this point I would have to agree with Mexs take on this.


    1800W continuous or up to 3000W surge, but the GFCI outlet is still a 20amp outlet. Interestingly, whenever it trips, it is IMMEDIATELY upon starting the microwave. As you mention, the GFCI trip is easily distinguishable from an overload - I am confident this is not an overload condtion.

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