twin power cords tripping gfi

[ramblin]

i have a 12 meter aft cabin with twin power cords. At my marina they have 30 amp GFI receptacles and when i run one line only all is OK. When I plug in line two (even if selector sw in boat is off) both GFI's on the dock trip. I've tried switching the power cords around but still the same thing. The fact that I don't even have line 2 turned on tells me it's not a short but rather something to do with the GFI's. Any idea?

[El L Sea]

Have the marina look at the pedestal. We once had something similar. Problem with the pedestal.

[WayWeGo]

Are there separate neutral bars in your panel for the two cords? If not, that would probably cause the pedestal GFCI to trip depending on how the selector switch is wired.

Do you have the factory wiring diagram and is it still accurate? If so, can you post a photo of the AC panel wiring and I will be happy to look at it.

[ramblin]

I hope i attached the file correctly of the A/C wiring diagram.

with the shore selector to line 1 and line 2 main breaker off, it would seem that line 2 white and black or not in the loop, only that green is going to bonding bar. I'm not very good at electrical but could it be a difference in in the green between the two power cords?

IMG_20200721_101226316.jpg (347.62 KiB) Viewed 9366 times

[El L Sea]

On our 1988 12m Sedan all neutrals are tied, which is correct.

20170914_092750.jpg (128.29 KiB) Viewed 9363 times

[WayWeGo]

Ramblin, I can't read the fine print on the schematic you posted. If there is any way to get a clearer copy, that would be great! Also a photo of your AC panel if you have it.

El L Sea, if you have a single power cord, having all the neutrals tied together is correct. If you have two cords, you cannot connect the neutrals together without risking the pedestal detecting a ground fault and tripping the GFCI.

A really good place to go for detailed boat wiring is https://gilwellbear.wordpress.com/ and refer to the directory on the right side of the page. Jim Healy has done a fantastic job of explaining an often complicated subject so the rest of us can understand it.

[WayWeGo]

The GFCI only looks at the current going through the line and neutral wires, not the safety ground (green wire). I don't think the ground has anything to do with it unless plugging in the second cable is causing some of the current that should go through the neutral to return on one or both of the grounds.

That makes me suspect you have the neutral and ground tied together somewhere on the #2 side of the panel. This would be common on a house panel, but not allowed on a boat. Maybe a previous owner was not aware of this?

[prowlersfish]

Very good info . I will be checking my panel .

[ramblin]

I've talked to other boaters in the marina and was asked how old my boat was (1989) and that they had issues before with a single grounded system with twin power cords. I read the responses and I'm thinking that when I turn on the 2nd cord it's ground and the 1st cords connect and cause the GFI's to trip. They said they replaced the dock breakers w/o GFI. Does this sound right?

When I'm at a marina w/o GFI's I don't trip the breakers

[WayWeGo]

That's a really bad idea! I do not believe you can legally replace the dock breakers with ones without GFCI. Even worse, it would be dangerous for anyone who was in the water near the dock due to electroshock drowning. I suspect the marina would be quite upset if they found out you had done that.

If you are tripping the GFCI breakers, there is something wrong on your boat and you need to fix it for safety reasons.

[WayWeGo]

Electroshock Drowning:

https://www.boatus.com/seaworthy/magazi ... lained.asp

Two deaths last week due to an electrical fault on a boat and bypassing the marina's safety system:

https://www.azfamily.com/news/boat-of-b ... de9e5.html

[P-Dogg]

That makes me suspect you have the neutral and ground tied together somewhere on the #2 side of the panel.

Perhaps in an appliance. Unplug all of them, then reconnect them one at a time.


But first, check the ground/neutral connection at the boat's shore power receptacles. What is the resistance between ground and neutral?

Mine read "open circuit" on ohm scale (on both my meters).

If you want to have even more fun, measure the current in the individual shore power wires. I made a contraption that exposes the individual conductors. Think short extension cord with no outer insulating sheath. Plug the boat into a non-gfci pedestal ( since you trip gfci immediately) with your test cord and your normal shore power cord connected in-line. Power up all the 120 volt appliances (you've got a panel mount ammeter for each shore power cord, right? If not, I highly recommend it). Put a clamp-on ammeter around each wire seperately in the special cord. Ground wire current should be zero. Hot and neutral currents should match.

Now the real fun begins, because ground wire current will most definitely not be zero. Zero is a very powerful quantity.

You can also put your clamp-on ammeter over your normal shore power cord while drawing a load. Again connected to non-gfci pedestal. I bet that it does not read zero either (#milliamplivesmatter). That means you are either sinking or sourcing current through the water, because all current should come and go to your boat via the shore power cord(s).

Armed with more data, you can now more finely search the internet.

Good luck, and do report what the problem is. That way it helps those folks who use the "search" function.

[WayWeGo]

Great minds think alike, as I have a couple of the breakout cables P-dogg mentioned. To see what they look like (I don't have a photo of mine and they are at the boat), go to https://gilwellbear.wordpress.com/categ ... for-boats/ and scroll down a little bit to see Jim Healy's version.