Jim H. You're making it way too complicated! It's a simple matter of current sharing. If the green and white conductors are connected at both the source and the load, some of the current will flow through the white and some will flow through the green, causing an imbalance in the current in the black and white conductors. It's just that simple. The reason it's not tripping the GFI when connected to shore power is either that the green wire has been cut in the shore power cable or there is a galvanic isolator installed. Obviously if the green is cut, there will be no flow in it and the GFI won't trip. Galvanic isolators incorporate a pair of back to back diodes in series so that no current flows unless the voltage across the isolator exceeds about 1-1/2 volts. This voltage is low enough to protect a swimmer but high enough to prevent the normal electrolytic voltage of about one volt from flowing in the green wire and protecting the dock and other boats tied into the safety ground. So in order for current to flow in the green shore power conductor with a galvanic isolator installed and a short between the white and green wire at the load, the voltage drop in the white conductor must exceed 1-1/2 volts. Something not likely to happen on a smaller load. So all that needs to be done to rectify the problem is to locate and open the short between the green and white conductors. It could be in the boats wiring or in a device plugged into one of the outlets. Tom Collins, Misty Sea

Tom, Maybe... A short between green and white is a leakage current due to a wiring issue on the boat. That is one cause - perhaps the most common cause - of a GFCI blowing, but it is not the only cause. And, actually locating a crossed-connection on even a small cruising boat is entirely another matter! I don't know if Jim's response to my last was also posted to the list. It appears he's isolated the miscreant behavior to a battery charger which is wired into the port-side wiring of the boat. He didn't say if he only runs that battery charger on the genset. He only said that if he doesn't turn that battery charger "on," the GFCI doesn't blow. I assume we'll hear more when he finishes his investigations. That could be the home of a hiding cross-connected neutral. Or it could be a defect inside the device, or an HF harmonic, or perhaps a non UL-marine device design issue. Or it could be that he has caps charging somewhere and that just changing the sequence of how he powers things up could circumvent the GFCI blowing. We can only speculate until he completes the hard work of running it down. We don't know enough to come to a conclusion on causation just yet. Depending on the outcome, you may well be correct that he will also have to verify the shore power service connections and GI in order to complete and close the TR. Thanks, Jim On Sep 10, 2013, at 3:06 PM, TW Collins <admiral@ktb.net> wrote: > > So all that needs to be done to rectify the problem is to locate and open the short between the green and white conductors. It could be in the boats wiring or in a device plugged into one of the outlets. Peg and Jim Healy aboard Sanctuary Currently at Rock Creek, Pasadena, MD http://gilwellbear.wordpress.com Monk 36 Hull #132 MMSI #367042570 AGLCA #3767 MTOA #3436