Stray Voltage?

westend wrote:

Using a compartment door hinge, unless it is connected to the frame, is a poor contact point.

One of the first measurements I'd be looking for would be continuity from the male ground pin on the shore cord to the female ground on the other end. This will verify that you have a complete ground path through the cord and eliminate one suspect.

Next spot would be the integrity of the load center-> frame ground. Loosen the attachment fastener, spray some penetrant on the fastener and lug, turn back tight. If you remove the fastener completely you can also measure for voltage or current from the removed load center cable to frame, if plugged in. If you measure any voltage above above 2V, you have a wiring or device problem in the trailer.

These ground fault problems can be tedious. You may have to remove ground wires from each circuit to narrow where a fault is located. The cheap RV receptacles are known for losing connectivity with wires just sitting in the walls.

Best of luck with your ground problem.

These are all good troubleshooting methods, but here's a few more ideas.

First of all, one of the most common causes of the EGC ground wire potential varying by several volts above earth is a secondary Ground-Neutral bond somewhere in the branch circuit, or simply reversed Ground and Neutral wires somewhere in the wiring. Both cases will do exactly what the code tells you NOT to do. That is, the EGC ground cannot be used as a return for load current, only fault currents. In a secondary ground-neutral bond or swapped ground-neutral scenario, the normal 5 volts of voltage drop on the neutral will end up on the ground wire. In fact, measuring between the EGC ground wire and an earth-ground reference while varying the load on that branch circuit is a good way to find load-bearing EGC ground wiring without taking everything apart. These mis-wiring examples are more common than you might think since they may not be obvious. I'm aware of these since I do diagnostics for large sound system power, and even 1 volt difference in ground loop voltage will cause all sorts of hum and buzz in the sound system.

A better test for the shore power wire's ground integrity is to use a 12-volt automotive voltage tester that looks like a screwdriver with a light-bulb in the handle and a alligator clip. Be advised that this test must be done while unplugged from any shore power, but it's perfectly safe since only 12-volts DC are involved. I use these testers "backwards" by putting the alligator clip on the positive terminal of the 12-volt house battery, then use the screwdriver tip to test the ground pin on the shore power plug and watch for a solid light in the handle. You can get one of these automotive testers for $10 or so from a local auto parts store. Here's one example. Test Light

The beauty of this current continuity test is that it drives maybe 1 ampere of current through all the ground connections, which you can then flex and watch for a light bulb flicker indicating a corroded or loose connection. Start the test on the shore power plug, then add on any dog-bone adapters and extension cords one at a time, while testing each time for ground continuity.

If you have an extra $300 to spend and do this type of diagnostics on a regular basis (like I do), then you can get a Ground Loop Impedance Tester. I use an Amprobe INSP-3 or Ideal SureTest Analyzer all the time, which puts a single cycle 20-amp pulse between the hot and ground wires, then gives you an impedance measurement. So you can confirm if there's less than 1 ohm EGC impedance all the way back to the service panel's ground-neutral bonding point. Works great and only takes a few seconds, but you really need to understand power distro theory to interpret the results.

Hope this helps. As the previous poster said, ground loop problems can be some of the most difficult to diagnose. But the above methods are part of my personal test procedures for power distro problems.

Mike Sokol
No~Shock~Zone