question

Jangeja avatar image

Multiplus 12/3000/120 use with only 1 hot leg of 50 amp 120/240 service

Hello everyone,

My use case is probably pretty unique, but here it is.

I’m converting a big box truck into an RV as a hobby of mine. I installed a 50 amp 120/240 receptacle on the vehicle and my idea for how the electrical would go is:

Shore power L1, L2, N, Gnd -> 50 amp 2 pole main breaker

Main breaker L1, N, Gnd -> subpanel

Main breaker L2 -> multiplus AC input

Sub panel N, Gnd -> multiplus AC Input

Multiplus AC output L1, N, Gnd -> subpanel (other hot leg)


Is there any problem with doing this? Any issue with the power assist since the neutral from shore power is forwarded to the subpanel from the main breaker

MultiPlus Quattro Inverter Charger
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2 Answers
Jangeja avatar image
Jangeja answered ·

Just in case anyone is wondering. I’ve answered this question myself.

I’m a self proclaimed electrical hobbyist, with a degree in computer engineering. I know that title holds no weight especially when working with heavy duty electronics like the multiplus. It’s something I enjoy which is why I took this project on, even if that means doing something potentially dangerous. I’m building an RV out of a used haul truck.

Well here goes nothing.

I can post my electrical diagram tomorrow, but here’s a summary of it.

I had my 50 amp shore power receptacle feed into my progressive industries surge protector. My surge protector fed the L1, N, Gnd to my multiplus, and I fed L2 from the surge protector directly into the 2 pole 50 amp gfci breaker. My multiplus fed L1, N, Gnd to the 2 pole 50 amp gfci breaker. The 2 pole breaker fed L1, L2, N, Gnd to my main panel.


Here is where it got interesting. I plugged my shorepower into a single pole 20 amp house outlet. The pigtail adapter for my receptacle essentially shorts L1, and L2 So they are electrically equivalent. When I plugged into shore power, with the multiplus in the charger only state, everything worked fine. My batteries were charging and my ac loads worked. However, when I switched the multiplus to on (inverter) something interesting happened. The house 20 amp gfci breaker popped. No matter what i did, the home gfci breaker would pop. Even with all of my trucks AC breakers turned off.

So that got me thinking. It couldn’t be a short or ground fault within my truck because none of my trucks ac breakers popped. In fact, they were all off! I started to think about a ground fault occurring from my shore power receptacle to my house plug. And that’s when I realized it was because of the neutral bond that the multiplus does when inverting mode.

Because I pass L2 from the surge protector to my breaker, it completely eliminates the multiplus’ inverter ability to unbond the neutral ground before passing on the neutral, line, ground from AC in. Also, even with my trucks breakers off, it would still trip the house gfci. This is due to a very small residual current flowing on L2, which the neutral ground bond existed still since the inverter was running. This caused my house gfci to trip, and none of my trucks breakers to trip because the ground fault occurred between my multiplus and the house breaker. Disconnected L2 from the surge protector, and everything worked!


Kind of a long read, but very interesting to a newbie like me. Would love to have some sort of a relay to pass through L2 from the surge protector without having to buy another multiplus, as they are quite expensive.

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mrseas avatar image
mrseas answered ·

You may want to consider removing the 50 amp GFCI breaker(s) and replacing them with non GFCI type. Some folks have reported issues with GFCI breakers and inverters. Plugging into a GFCI socket and running that through a GFCI breaker may have something to do with your issue. If You do try it please report back and let us know what happened.

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