Ted G

iTrader: (1)

I kind of agree with Steve, it seems like you have some current leakage and it's only gonna get worse. What the lift guy told me about the galvanic corrosion is that the bolts corrode inside the pilings when moisture wicks up the pilings it is like the bolt being immersed in water. The current then travels through the lift when it's plugged in, through the bolt, and trashes the bolts, eventually the lift falls off the piling. They now install all their lift motors with short pigtails and plugs so you can unplug the lift right at the dock to prevent this. If you want go over to cbpba.com and ask about an electrician over there, I think there are a few in the club that could help.

GregP

First thing I checked was between the electic supply lines, both the lift 220 circuits and the 110 dock outlets, to the dock fittings, stair and bolts to see if there might be a short somewhere in that wiring, and there is no voltage between the AC grounds and anywhere on the dock or the lift.

bcarpman

Here's a couple of good links on Corrosion, but there's a lot of info there on electrical issues as well (since that's what causes corrosion), and how to properly wire your boat/dock.

http://www.boatus.com/boattech/MarineCorrosion.htm

http://www.boatus.com/seaworthy/galvanic/default.asp

GregP

After several hours with the DVM (and several more re-wiring) I finally tracked down the problem and corrected it. The short answer (no puns) is that the shore power line passed though an under-deck conduit along with several DC leads and the conduit had water setting inside in a low spot (which I've blown out with compressed air as best possible to try to dry it). Even though there were no breaks in the insulation, the resistance between the AC and DC circuits when wet (even though all the wire is boat/wet use rated) was only about 50,000 ohms.

I pulled out all the shore power wiring and re-ran it separate from the DC lines in adels inside the hull sides instead of in the underdeck conduit (I had to move the inlet recepticle, so I will have to patch the old mounting hole in the center console sometime).

I did confirm that, once the voltage leak was eliminated, the shore power ground is tied to the boat DC ground through the battery charger. Once re-wired the AC hot shows 110 VAC to the boat ground, and the AC neutral and ground both show about 3-4 VAC.

The thing that surprised me most is that a coil of wire laying on the deck, connected to nothing and pulled out of all the conduits, still showes a 4-5 VDC potential to the boat ground. The resistance between the wire just laying there and the boat tests out about 500,000 OHMs which is the resistance of me holding the leads.

Anway, after spending a lot of time proving that the boat sitting on the lift in mid air is not quite at the same potential as a true ground I was able to get everything re-wired and behaving as it should.

Thanks to everyone for the suggestions and lthe links.

-Greg