IDENTIFYING THE PROBLEM
So what is happening when you plug into shorepower, the pedestal trips, and suddenly you have no air conditioning? We know from these illustrations that an imbalance exists between the hot and back to ground through the green wire and through the water. Here are the possibilities:
1. At least one piece of AC equipment has a dangerous short between the hot and the equipment, in which case the black wire is making contact to ground where it shouldn’t. You haven’t been shocked either because you haven’t yet touched the wrong thing at the wrong time or because the green grounding wire is safely carrying away the bulk of the current.
2. You have at least one connection somewhere—and maybe several—between neutral and ground, allowing enough current imbalance to trip the ground fault device. 3. Both of the above. By placing a sensitive ammeter around the hot and neutral wires (fig. 7), excluding the green grounding wire, an imbalance can be detected. In the boatyards, we plug the shorepower cord into an adapter that we make up, with the green wire separated out. The ammeter must be capable of measuring current flow as little as .004 amps, and those meters cost somewhere in the range of $500 to $600. The test can begin by plugging into shorepower, turning on all AC breakers, and activating all AC loads. In other words, its not enough to turn on the air conditioning breaker; you must make sure the compressor runs. This test will provide a snapshot of the overall condition, and any reading above 4 mA indicates a problem. Of course, plugging in sounds easier said than done. It won’t be possible to run the test at a pedestal that immediately trips.
Before going down this rabbit hole, remember that the ground fault device on the pedestal trips when the total imbalance exceeds the rating. Let’s assume a device rated at 30 mA (even though some marinas have those easily tripped GFEPs rated at 5 mA). You arrive at the marina, plug in, and just like that, the device trips and several other boats lose power because of you. You’re the problem child and others on the dock glare at you. It is quite possible, however, that some if not all the other boats also have small neutral-to-ground leaks. Perhaps those leaks add up to 25 mA, or just under the trip threshold. You add