Need expert electrical advice for GFI problem, please

[Frank Langer]

Hi,

Everything has been working fine on our 1984 E30+ until we moved to a new yacht club slip today. When I plugged in our shorepower cord to the 15 amp service the Ground Fault Circuit Interrupter on the dock immediately tripped. I turned off all electrical switches--the main AC, the charger, both DC battery switches, but still the GFCI tripped.

Folks on the dock and Nigel Calder's Electrical and Mechanical Manual suggested it is likely moisture in the shore power connection. I undid the shore power cord wiring, dried thoroughly with a heater and reconnected the shore power cord wiring. With the shore power cord plugged in at the dock but not on the boat, the GFCI did not trip, but it tripped as soon as I plugged it into the outlet on the boat even though all the electrical switches on the boat were turned off.

I then disconnected the shore power input wires--positive, neutral and ground--at the AC panel main breaker and bus bar. When I plugged in the cord at the dock with these wires disconnected, the GFCI did not trip. When I reconnected the shore power wires at the main breaker, the GFCI tripped again, even though I think everything is turned off. Could a faulty main breaker cause this problem?

A local boat mechanic/generalist suggested that sometimes the reverse polarity wire can cause this problem and suggested disconnecting it, but that didn't stop the GFCI from tripping.

A local electrician suggested that I systematically disconnect the wires in each AC circuit--the hot water heater, charger, recepticles, etc. to see if any of them are responsible for the GFCI tripping. That sounds reasonable, so I'll try that next.

But I could sure use advice or tips from anyone who has faced this problem or knows anything about detecting a GFCI fault.

Thanks in advance for any help!

Frank

 

[Loren Beach]

Our experience, FWIW

This last year we have converted a major number of our club's shore power posts to the new standard GFCI type. Several boats started having tripping problems when they had not had that happen in the past. We have a couple of electricians in the club and their best guess was that there was some tiny current leakage on the individual boats and that the owners needed to go through their AC system and trouble shoot until the problem was found. Failing that, there is a slim chance that the offending GFCI breaker itself was defective. I recall that out of over 70 outlets maybe one or two were replaced.

So, inconvenient as it is, the wiring on your boat needs to be checked out, circuit by circuit. You have done a lot already.
Nuisance project, but it's gotta be done.

One other piece of "breaker trivia" that we all had to learn was that these new types trip easily - even a light touch to the toggle might trip it. Worse, once it's tripped you can NOT reset it by just flipping it back to the "on" position.
If you do this it will refuse to reset, even if it seems to be in the right physical position. You have to move the toggle over firmly to the "off" position, count to ten, and then move it back firmly to the "on" position. That seems to work.

Best of luck to you.

Loren

 

[Frank Langer]

Thanks, Loren,

That's sort of what I'm thinking as well. I did test our shore power cord plugged into a neighbouring dock outlet which had not tripped with that boat plugged in, but it did trip when I plugged our boat in that outlet, so I'm thinking it's not a faulty dock outlet but rather some previously unknown problem in the wiring on our boat. Am I correct in assuming that the problem is only in the AC wiring, not in any of the DC circuits--bilge pump, cabin lights, water pressure pump, battery wiring, grounds to the engine,etc.? It would certainly decrease the scope of my investigative work if I can ignore the DC system and focus on checking the AC circuits.

Also, can a volt meter electrical instrument or any other tool help to locate the problem or is the best way simply to disconnect each of the circuits and test if the GFCI still trips?

Thanks again!

Frank

 

[bradh]

Some Thoughts........

Breakers trip when an amount of current passes through them; GFCI trip when the amount of current going through the hot is different then the amount of current returning through the neutral. Current in via hot must = current out via neutral; a difference in these indicates current is being lost somewhere.

The new GFCI may be more sensitive to the amount of imbalance. Possibly you have some place where your neutral and ground are tied together or are nearly tied together. This would allow current to be returned through the ground and would trip the GFCI.

Check the the resistance between the common and the neutral at the main boat panel (without shore power connected). It should be pretty high (in home wiring it will be very low as they are tied together at the breaker panel). You might try comparing your measured resistance to other boats in the marinia. I am guessing that your neutral at some point crosses your ground wire or pad.

Brad

 

[Frank Langer]

Thanks, Brad. I'll try that tomorrow and will look for any possible leakage between neutral and ground wires. Any additional advice is still very welcome!

Frank

 

[Frank Langer]

Thanks for that additional information. So if it's leaking into the ground, the DC system or into the water, what's the best way to find that leak? My current plan is to disconnect each of the AC circuits--hot water tank, charger, receptacles, etc. -- to see if that disconnect allows me to plug in the shorepower cord without tripping the GFCI. Then if I find a circuit which, when disconnected, affects the tripping of the GFCI, I will check all the connections to ensure all wires look good, connections look good and no wires touching each other when they shouldn't.

Does that sound like a reasonable approach or is there an easier or better way to solve this problem?

Thanks for all your replies so far--I really appreciate the help after a long day of little progress!

Frank

 

[Christian Williams]

I know nothing, but I would borrow somebody else's dock power cord and try that.

I know of two cases in which the power cord looked fine but shorted out, including Mark Herrcat, whose cord literally blew up one night last year while he slept in his bunk in the slip.

 

[Frank Langer]

Thanks, Christian, I will borrow a cord as you suggest. But I will be surprised if it's the cord because I took apart, cleaned and reconnected the end of the cord and then tested it with my voltmetre--I had 120 volts as it should be. Also, when I connected the shore power cord but disconnected the hot, neutral and ground wires in the AC panel, the GFCI did not trip, but when I reconnected the wires in the AC panel, the GFCI tripped again. So I'm thinking it has to be in one of the AC circuits. I'm puzzled though as to how this can be because the main breaker and all other electrical switches are turned off, and the GFCI still trips--there should be no electricity flowing at all! I wonder if the main circuit breaker could be faulty, but I'm only guessing now.

Thanks again!

Frank

 

[Tom Metzger]

I wouldn't worry about the hot leads. The problem is in the neutral wire and the ground wire. Somewhere on your boat there is a connection between the neutral and the ground which allows enough current in the neutral wire to trip the GFCI. It doesn't take much. Less than 0.004 amps.

Lift the all of the branch circuit neutral leads and reconnect them one at a time to find which is the problem. If with all of the neutral leads off the GFCI trips then I obviously don't know what I'm talking about.

 

[Frank Langer]

Thanks, Tom. I'm assuming you mean all the neutral wires in only the AC system, since it's the AC shore power GIFC that's tripping. Others have suggested that maybe it's leaking into the DC system, but if I can find the source of the leak in the AC neutral wires/connections, that should solve it if I understand your post above.

Removing only the AC neutral wires would save me significant time, so I like that suggestions. I sure hope I can find the problem this way! In reading about troubleshooting GFCI tripping on the internet this evening, I'm finding that lots of boaters have this problem and it's hard to solve, sometimes being even in the way the boat was constructed rather than a fault developing. I hope I can sort it out.

Thanks again for your relpy!

Frank

 

[bradh]

That's an idea

Tom (and your dockmates) have a good point. If your AC side is not isolated from your DC side, you could be leaking current from the AC neutral onto the DC side. In addition to checking the resistance (aka continuity checking) between your AC neutral to AC ground, check the resistance between the AC neutral and the DC negative (drag the shore end of the power cord over to your negative battery terminal is one way to do that). Both values should come back very high (MOhms).

Brad

 

[Frank Langer]

Final outcome--Ground Fault Circuit Interrupter problem and fix

Hi,

Thank you all for your helpful input. After doing some of the initial investigative work yesterday and this morning, I hired a local marine mechanic/electrician that I have used with success previously to confirm what I was finding and help me find a good solution and we did.

By checking each of the AC circuits we identified the one that when disconnected, didn't trip the GFCI switch on the dock shorepower. It was the circuit with an older Heart Interface Inverter/Charger. When we removed it we found some "fried" inside parts. As fixing it with new parts would still leave me with old technology and would be about as costly as buying a new inverter and charger, I opted to buy new. When we installed this, all the electronics worked without tripping the shorepower GFCI switch--success!

Electronic stuff that can seem so daunting can often be solved through a systematic problem-solving approach one step at a time. While I believe this, I still find some of these problems daunting.

Thanks again for all your replies!

Frank

 

[Tom Metzger]

This would be the DC leak fault that was brought up as a possible cause for the GFCI trip.

The facts are:

I turned off all electrical switches--the main AC, the charger, both DC battery switches, but still the GFCI tripped.

There was no 120 VAC voltage; there was no 12 VDC voltage.

The leakage was between the AC neutral and the shore ground. The voltage powering this leakage current comes from Frank's boat being a long ways away from the point on shore where the neutral is grounded. The neutral is carrying current from other boats so there is a voltage drop on the wire. You can measure this voltage.

The GFCI tripped because there was current on the neutral and none on the hot line. The cause could have been any grounded device, or as Christian suggested, a cable.

 

[eknebel]

As always, Tom is right. It is not uncommon to find 1 to 1.5vac measured neutral to ground, caused by poor connections, or overloading.

 

[Tom Metzger]

As always, Tom is right. It is not uncommon to find 1 to 1.5vac measured neutral to ground, caused by poor connections, or overloading.

I must have bought Ed a beer when I was in Annapolis last year. Nice guy.