Problem Solved - Using GFCI for Shore Tie
I have had my Roadtrek 3 years and it has always had a problem tripping GFCI outlets used as shore tie. I have run down many a rabbit hole trying to find the cause and rectify the problem. I owe much of my recent success to fellow forum member "Booster" who is one of the most knowledgeable folks I have met on RV electrical.
I have also seen many posts on this forum and elsewhere describing problems using GFCI's for Shore Tie power. My remedy has been to carry a standard plug with me and swap out the GFCI at the homes of friends (with permission of course) while I was hooked up.
So I was between trips for a few weeks and decided to really dig in and find the problem. First, a few facts about GFCIs and why identifying a cause can be so elusive:
A ground fault circuit interrupter is a protective device specifically designed to break the circuit every time there is an imbalance between incoming and outgoing current. The GFCI responds to a fault by breaking both the Hot and Neutral legs in the circuit. Because a GFCI measures and responds to current in the Neutral leg, in searching for a faulty circuit, you cannot simply turn off breakers to see if the fault goes away.
What frustrated me at first was that every 120v breaker was open and the tripping still occurred. To find the at fault circuit it is necessary to isolate each neutral from the bus inside the distribution/breaker panel. To do this secure all 120v sources (including generator and inverter - especially if these are set to come on automatically). Use a tester set to resistance and measure from the Neutral Bus Bar to the Ground Bus Bar. If this reads any continuity (resistance other than Open Line or OL) there is a circuit connected that is the cause of the problem. With no power source connected, the Neutral to Ground Bus Bars should show Open Line (infinite resistance).
Selectively remove the neutral wire from one circuit at a time and recheck the reading. When the resistance across the bus bars goes to OL, the disconnected circuit is your problem. Check the disconnected circuit Neutral to Ground wires and you will likely see some continuity.
In my case for all this time it had been the electrical side of the Hot Water Heater. I have a Suburban SW6DE which runs on 120vac and Propane. it also has 12v control system (although 12v does not heat the water, but operates the controls and propane igniter).
I found multiple problems with the heater. I had assumed the water heater was propane only (which functioned fine) and never noticed the electrical components that were well hidden. I had wondered why I had a breaker labelled Hot Water Heater and thought maybe it was mislabeled.
I believe the water heater had been energized (on electric) with the tank empty (by a previous owner). This would be easy to do because it the 120v and 12v systems have independent thermostats. The Roadtrek control panel has a Hot Water heater switch, but this only controls the 12v side. Turning off the 12v switch does not turn off the 120v - that must be done using the breaker or the cutoff switch located on the back of the heater. Turning on the 120v side with the tank empty, or emptying the tank with the 120v side still energized will instantly blow the element. In my heater this historical event also partially fused the well hidden 120v cutoff switch, melted a solid wire jumper on the 120v thermostat, and blew multiple holes in the heating element. To remove the element and cut off switch the gas burner tube and manifold tube have to be removed. In that process the manifold tube broke off at both ends, so I ended up replacing those components as well.
The pics show the blown heater element, the location of the switch and element and the completed unit with the burner tube hiding the electrical components.
Another note on Neutral to Ground Bonds. Each 120v Source should establish its own N-G bond when it is on line. Shore tie is easy, it is made in the main panel where the Neutral and Ground Bus bars are connected. Your generator and inverter can be checked by first checking the Neutral Bus to Ground bus with all 120v secured, and should read OL. When either the generator or inverter are on, there will be a continuity showing across the two bus bars. If per chance there are multiple simultaneous Neutral to Ground bonds when the shore tie is connected it can cause a GFCI trip. An Automatic Transfer switch that breaks both the Neutral and Hot legs should prevent this hazard.
Since making the repairs, I have been able to successfully power the Roadtrek from a GFCI outlet.
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