question

I am having a similar issue.

As far as I can tell, my travel trailer operates just fine without the inverter, and does not trip any GFCIs I've been connected to. However, when I install the inverter, it trips the GFCI at various times. I can not consistently isolate a piece of equipment on the trailer side. e.g. I turn off all circuit breakers except the 50A mains from the inverter and then run one AC appliance at a time. I am able to successfully run each appliance from the garage outlet. I start adding a few appliances together, in no particular order, and it trips. Additionally, when storing the trailer, I turn off the two 50A main circuit breakers to the distribution panel, cutting off AC power to the rig, and place the inverter in charger only mode. It will bulk charge the batteries at 100A (limited by my settings), absorb and float normally; a few days later, it will trip the GFCI for an unknown reason.

I reached out to another individual who owns this model in their 5th wheel and they have no GFCI issues; their setup is practically identical to mine. I initially was thinking my new trailer had a ground fault; but after isolating each ground and neutral, and testing each appliance individually, I am back to the inverter as the cause. From what I can tell, the inverter leaks to ground, and when combined with multiple appliances, trips the GFCIs.

Any assistance would be appreciated.

@eluttkus I solved this issue. I had not properly grounded the Multiplus II to the frame of my camper. I ran a single strand of 6 AWG solid copper wire from the stand alone ground point of the Multiplus II frame and used a self tapping screw to attach it to the frame of my camper. Problem solved! I continue to be reminded that improperly grounded equipment will sometimes exhibit the strangest behavior!

I know this post is old, but I'm having a similar issue and wanted to post here for a couple of reasons: 1) someone might have an idea that would help, 2) my conditions are a little different and I want to be sure others don't have the issue so I will post back when I solve the issue.

My system is new and also installed in a Grand Design fifth wheel. It is a MultiPlus-II 24/3000/70. My Grand Design RV had the external shore power (a 4-wire cable) going to the breaker box with the white going to a neutral bus bar, the red and black going to their respective sides of a WFCO breaker panel and the ground going to a ground bus bar. As I remember, a wire goes from that bus bar to a common chassis grounding location where three grounds are tied to the chassis and there is red spray on the connectors and chassis (I assume this is some kind of no-ox anti-corrosion spray to keep the copper and bonding at a few milliohms).

I removed this wire and put it to the AC IN of the MPII (through a breaker on L1/L2/N), BUT I pulled the ground out and connected it directly to that chassis bonding point rather than running to the MPII. I then took a large solid copper wire and ran it from the MPII ground lug to the common chassis ground. The AC-Out of the MPII goes to the WFCO breaker box as before. I believe there is a ground wire from the ground bus in the WFCO breaker box to the common chassis ground and I will check this tomorrow. I did not connect anything to the PE connections on the MPII. So the only Earth connection is the large ground lug going to the common ground point. It seemed silly to run both of the AC-In and AC-Out grounds to that lug or to the chassis lug (to me anyway).

The thing that is different for me is that the unit runs a while before it faults. I have checked the power outlet with a soldering iron and it runs for days so it's a "legit" problem. I am connecting to the 15A GFCI receptacle with a 3-prong to 30A plug, then I have a ~25' 30A cord, then a 50A to 30A adapter and then camper's 50A supplied cable. I will check ground conductivity through all this tomorrow. The 15A to 30A adapter is loosely fitted except for the ground which is practically stuck in the outlet.

System drawing attached (of course it doesn't show the all-important ground connections!): 390RK Solar-11.drawio.pdf

Install picture (MPPTs and distribution are not visible):

System happily working in Assist mode (it's dark outside so no PV action at the time of the photo):