ground fault feed to motorhome trips

[rimrie]

With the Main breaker on the distribution panel off the GFI outlet feeding the motor home trips. If I disconnect leads at breaker GFI trips. Disconnect leads feeding panel at transfer switch GFI does not trip. Disconnected leads between transfer switch and distribution panel and ran a temporary feed from the transfer switch to Panel main breaker (open), GFI trips. Disconnect temperary leads from main breaker, GFI trips. output Jumpers to generator contractor left connected throughout this process. Can there be anything causing a ground by tightening the leads at the contactor?

 

[Alfa38User]

If the outside power to the motor home is off (via the breaker or unplugged), a GFCI outlet cannot trip BUT it will not reset from a previous trip either. A GFCI  outlet requires power on it before it can be reset. Be careful of an ordinary extension cord lying in damp grass (for example).

The electric Fridge heater element or the electric side of the water heater element are often found to be the culprits for GCFI tripping if it is the home GFCI. Most simply choose to power the motor home using a non-gfci outlet from the house if that is the one tripping.

For the motor homes own GFCI, the patio (often the culprit) or other outlets that are daisy chained to it may have moisture in them causing it to trip. Up to 6 ordinary outlets (with no test buttons) can be powered from one GFCI equipped outlet. The usual GFCI protected outlets are located in the bathroom (sink), kitchen counter, and patio but there may well be others like the outlet behind the fridge, depending on how the manufacturer wired the motor home/trailer. Not all are well designated with those little stickers. (Mine has NO stickers)

Can there be anything causing a ground by tightening the leads at the contactor

Not too likely but if stranded wire under a screw head is being used, watch carefully for a strand or two that can sneak out from under the connection.

 

[rimrie]

Found a stray screw that had dropped into the hole where the romex cables come up behind the refridg. that had rubbed through the white insulator and the ground paper. Apparently there is a potential difference between neutral and ground. Thank God for my looking down that hole.

 

[Lou Schneider]

It's not a difference in potential between neutral and ground.  GFCIs work by comparing the current going out on the hot wire to what's coming back on the neutral.

Both neutral and ground are at 0 volts.  With the screw shorting the two wires together, the return current had two paths to return to the main panel.  Part of the current went on the ground wire, reducing the current on the neutral wire.  Since the current on the neutral no longer matched what was being supplied on the hot wire, the GFCI tripped.

Congratulations on finding the culprit!