House GFI trips when I run MH generator

BTW All RVers should plug their rig into a GFI periodically, many CGs have a 20A GFI. Turn all appliances on/off to help verify any potential problem.

There are periodic posts with someone getting shocked from their rig frame. So a ground fault and open ground (which can easily occur on any CG pedestal) could be a shocking experience.

ktmrfs wrote:
However, when under generator power, the transfer switch connects the trailer ground and neutral together, just like the main breaker panel in your house.

So when the transfer occurs, there is a moment when the house sees ground and neutral shorted before it disconnects the house hot and neutral feeds. Bingo, house GFI trips.

Good explanation. But the ATS should be a break before make relay. Both the hot and neutral shore lines should disconnect before the gen hot and neutral connect. Ditto for both hots on 50A.

I'm also wondering if you could have some appliance situation causing the problem. Try turning off all CBs in the rig - does the problem still occur? Have you used a household analyzer to verify that all plugs in the rig are wired correctly? While buying my rig the kitchen plugs had an open ground. Turned out that Monaco had not connected the grounds in the slide out junction box, so simple fix.

And it's a potential backfeed problem that needs to be resolved.

I'm kinda mystified too. My rig when on shore power feeds through the transfer relay which is in the normally deactivated position, when the generator is started, a time delay switch(solid state, non-adjustable) energizes the transfer relay coil and switches from shore to onboard. The relay is designed and set to brake both sides of shore power, pass through an non-contact phase and then close the generator line side supply to the converter. Note: line and common only, not earth or chassis grounds are involved. In trade terms it is a break before make relay.


I don't have any reference material with me but I bet that the AC + and -, are breaking and there is cross feed between the grounds. Too many times there is a problem discussed here when using a GFCI outlet at home on in a campground.

There are CEMF when the converter chargers energize and de energize and the spikes may be following nthe grounds.

I suspect what may be happening is that when the transfer switch goes between house and generator, there is a moment when the house GFI sees a ground neutral short in the trailer. Which will trip a GFI.

Why is this happening?? Well, by code the trailer ground and neutral are isolated, just like all the outlets in your house.

However, when under generator power, the transfer switch connects the trailer ground and neutral together, just like the main breaker panel in your house.

So when the transfer occurs, there is a moment when the house sees ground and neutral shorted before it disconnects the house hot and neutral feeds. Bingo, house GFI trips.

However, normally the generator is second in line behind the shore power so the generator shouldn't switch on or trigger the transfer switch unless you loose shore power.

darsben wrote:

sch911 wrote:

enblethen wrote:
You should be un-plugging the garage power or any shore power before starting genset.

I agree it sounds like a bad transfer switch holding both sides on, but you shouldn't need to unplug from shore power to run the generator. After all that's what the transfer switch is for in the first place!

You do need to unplug or at least turn off the shore power before the generator picks up the load. It is an automatic transfer switch made to go to shore power first then genny if NO shore power available.

At least that is the way it is on my Southwind

For safety reason there should be NO BACKFEED through shore power cord.
Electrocution hazard

sch911 wrote:

enblethen wrote:
You should be un-plugging the garage power or any shore power before starting genset.

I agree it sounds like a bad transfer switch holding both sides on, but you shouldn't need to unplug from shore power to run the generator. After all that's what the transfer switch is for in the first place!

You do need to unplug or at least turn off the shore power before the generator picks up the load. It is an automatic transfer switch made to go to shore power first then genny if NO shore power available.

At least that is the way it is on my Southwind

I would think it has to be the when transfer switch opens or closes the contacts to the shore power line is causing the GFCI to trip. I don't think you have a problem. Just The GFCI doing it thing. As posted above disconnect your shore power before starting Gen.

enblethen wrote:
You should be un-plugging the garage power or any shore power before starting genset.

I agree it sounds like a bad transfer switch holding both sides on, but you shouldn't need to unplug from shore power to run the generator. After all that's what the transfer switch is for in the first place!

Your transfer switch is trying to energize from the genset while there is power coming from the garage.
You should be un-plugging the garage power or any shore power before starting genset.

I am not sure if I understand your comments or not...

Are you saying while you are still hooked up to the house/garage 15/20AMP receptacle using a RV30-15A Adapter that when you fire up your motorhome installed generator you trip the breaker in the house/garage.

I am also aware that the MH should have an active POWER TRANSFER SWITCH that would separate the trailer 120VAC circuits and the 120VAC shore power cable when the MH generator starts up.

If you are truly backfeeding the house circuits I would expect the house/garage breaker to trip if the MAIN HOUSE/GARAGE circuit breaker is still bringing in commercial power for the house.

You would be feeding the house electrical system with two separate 120VAC sources at the same time. Something has give up????

IMO There is two things wrong with this type situation... The most important reason to always flip the house main circuit breaker when feeding the circuits with an external generator is to protect any electrical workers on the commercial side working on the lines or equipment near your house. They have no idea the line coming from your is ACTIVE being fed by your generator. This is why most house emergency setups all use a POWER TRANSFER SWITCH either manual or automatic when connecting an external generator to the house circuits. The other reason is you may be in big danger of having your external GENERATOR blow up on you. Obviously the commercial power feeding your house is much stronger than your external generator and guess which one will lose the battle...

If I have misread your comments than disregard all of the above....
I am no expert on this subject - just an Illinois Corn Field Plow Boy from Horse Creek country...

Just my thoughts here
Roy Ken