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A few on this forum were very helpful in helping me try and figure this one out last fall. But I am still not there- and am ready to splash down!

I am attached to dockside power- 30am cord to a 15 amp pigtail coverter to a dockside GFI outlet. I have used this outlet and these cords in the past without a problem. All of my circuits (except one) are functioning fine- I tried each. My problem is when I turn on the "AC Lights" switch which is supposed to turn on the galley light. This causes the GFI receptacle at dockside to pop. I reset it, test every other sircuit- all good, and then try the "AC Lights"- same thing, it pops. So I trust the GFI is doing its job and the problem is on the boat. One other symptom- when I pulled the prop, I felt the tingling sensation of some current- not terrible- but some.

I am not running any household appliances that might bridge ground to neutral.

So methinks I have a ground to neutral short somewhere on that circuit. I am not sure exaclty how to test it out though. Could it be the rocker switch itself? One of the light fixtures on the circuit? Something else? I KNOW THIS IS A DANGEROUS SITUATION, WHICH IS WHY I ASK FOR YOUR HELP.

Any ideas would be appreciated.

You could be right in a short to neutral to ground. To test it, disconnect the A.C. power. Remove the bulb or bulbs in question and go to the breaker and turn it off. From the load side of the breaker, take a ohms meter and go between Gr, N & Hot. You should read all opens and no shorts. Remember, a GFI only needs about 5 milliamp to trip. You could have corrosion in the lamp base or else were, in other words, leakage, not a complete short. The way you described it, the problem is in that circuit. If all else fails, you could rewire it.

When you got hit with current, when removing the prop, the GFI should have tripped. You don't have to tell me, but did it?? If it did not, I would be concerned.

When I got the current from the prop, I was out of the water and plugged into a nonGFI receptacle. I won't take this test in the water!!

Boat is 10 years old so corrosion not too likely, but this is a boat, right?

I will do the test you described. Test is only on that circuit right? (I don't need to be concerned with others) If from the panel I read a short (with bulbs and switches all off or out), then where is the most likely source of the short? I gather that based on what I described, this issues is somewhere between the panel and the end of this circuit right? So if I go switch by switch, fixture by fixture, I will find it eventually. Problem could be the switch itself too, right?

The tingling prop is what worries me most. Do you think based on what I described, these two are definitely related?

Thanks so much for the reply.

You are on the right train of thought! You do want all the switches in that circuit turned on. Again, pull all the bulbs out, if you don't, the filament in the bulb is connected between H & N and the ohms meter will see this as a short between the 2 wires. Yes, test only that circuit, as you stated it only trips when this one circuit is used.

Yes, is is a boat, I think . Thats way I try to make all my connections as water tight as I can & only use tinned wire. I just got my new boat and I am adding LED lighting, GPS, windllass... I am surprised, how much of the wiring is NOT tinned!! Marine wire is tinned & yes this is a boat.

The in the water thing scars me!! It COULD be coming from the boat next to you too. But thats just a guess, is your drive showing signs of corrosion? That would tell you too.

I will give the test a shot. Thanks for the help. If it turns out this is a neutral to ground short-would that explain the tingling in the prop? I think so.

Also- lets say the neutral on by rocker switch had disconnected itself, but hadn't made contact with a ground (not a short). Would that trip the gfi (i think so)? If yes, it would mean the prop tingling and this GFI are unrelated which means 2 problems instead of one.

Gotta love boating.

Thanks again for the advice.