sorry up front at this may get a little long winded
First- Our boat has been in an "amentity free" harbor since '06. We don't even have culinary water. The entire dock consists of 22 10x20' single slips, we're at the end of it. the first 2 years our power supply consisted of running extension cords from the utility building about 200 feet away, which itself was connected to temporary power. in 2008 the harbor got a decent power supply installed, after that, I ran some 8 gauge wire from the building to the dock, and installed a 30 amp plug. From there, I ran the boat power using a 10 gauge contractors extension cord. Our boat has two 30 amp input plugs, and I rigged up a junction box that allowed me to feed both inputs using the same cord. When I installed the 30 amp socket I attempted to install a GFCI breaker, but it always tripped. So I just installed the outlet without the GFCI. There are three GFCI's in the boat, and they operate properly without issue. And I've otherwise had no problems with the power. In 2009 I ran all new 8-3 wiring directly to the boat, from a 50 amp knife switch electric box that's attached to the building. The two hot leads split at a junction box at the boat, and each lead feeds a 30 amp outlet. I've had absolutely no problem with this setup. I find no ground leakage, I've checked hull voltage and voltage from the hull to the water several times and I've never found any stray current other than a few millivolts.
Our friend sold the harbor in January, and now we have new owners. The Harbor property is leased from the state, and they will be doing an inspection soon, so I thought I should upgrade the boat's power connection. I picked up a 50 amp GFI service disconnect box, and an electronic kilowatt meter which I mounted inside a Hoffman fiberglass electric box. I spent the afternoon Sunday installing the box, running conduit and wiring, only to have the same problem with tripping the GFI breaker once it was all connected.
FWIW, yes, I'm still using the 8 gauge and I know I should be using larger, but this has always been at my expense, and the new owner is planning on installing "official" dock power within the next 2 years. Until then, this should continue to get us by.
Part of the new install included hammering a new dedicated eight-foot long ground rod just below where the box is mounted. The incoming power was originally connected to a large A/C unit, consisting of two hot leads and a neutral. The ground and neutral connections are separate in the new box. I ran several tests with the voltmeter; neutral to each hot measured 122 V, ground to each hot the same, and even though they were not connected within the box, the neutral and ground wires showed continuity. With power off I also checked continuity between all the box connections, everything was fine. All tests were made while the boat was plugged in. Interestingly, I found that the breaker would trip even with either or both load wires disconnected from the breaker. Only the neutrals were connected. I disconnected the GFI neutral test wire, and the breaker was fine until I touched it to the neutral bus bar, then it tripped.
Once I unplugged the boat, the breaker didn't trip.
As I understand how GFI's work (like from this online explanation): "In normal operation the current that flows in from the 'hot' wire must return in full through the 'neutral' wire, and only way there could be an imbalance in the amount of current flowing in to the hot wire, and the amount of current flowing back through the neutral wire would be if an external source is adding current or current is being leaked through an external source.
-- How can there be any current for the GFI to measure when the loads are disconnected? If there's no current, why is the breaker tripping?
Any ideas on where to start looking?
Thanks in advance!
Here's a pic of the new setup--