Rewire AC Shore Power

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April 2004 -- I wanted to add a Galvanic Isolator in the AC shore power line, and replace the wire at the same time, since the old wire was ... well ... old.

This Galvanic Isolator was on sale at Defender. It was a good deal because it doesn't meet current ABYC specs which require an integral
real-time tester with an LED display.
I'll take my chances.

It's screwed into a marine plywood plate that's epoxied under the starboard coaming. Note the standoff pieces of wood to allow air flow for cooling, to protect the diodes.

Once everything was apart,
the heat created by the resistance in the corroded wire was even more apparent.

It had melted the jack.


I think any boat that's been in a salt water environment for 20 years or more needs a serious wiring inspection.

A new plug rebuild kit was $20, vs. an entire new jack for $60. Of course the rebuild kit on the right was for a different jack than the one I have (nothing's easy)
so I reused everything except
the actual plug fitting.

I didn't want to replace the whole jack, because I just didn't feel like spending more money today.

Ya gotta pick your battles.

Here's where things got interesting!

Under the protective cover for the Marinco shore power jack, I found
an excellent example of corrosion.
In fact the corrosion had increased the resistance on the 'neutral' wire
to the point where it had
melted the cover on the wire.

Well, at least I know I don't have reverse polarity. (grin.)

I didn't bother to strip the wire back, but in other cases I've seen corrosion like this extend back as far as ten feet into the wire. The moisture wicks back along the strands.

I feel better about my decision to rewire the boat. 25 years in a salty marine environment takes it's toll.


Also, Note the smaller green wires attached to the terminals. I added a test lead from each terminal that leads back to the Nav Station, so I can connect a multimeter to them occasionally and test the diodes without crawling around in the stern.

[To test: With Shore Power Disconnected, place an Ohmmeter across the terminals.
Note the reading. Switch leads, and do it again. Ohm readings should match.
With the Multimeter in Diode testing mode,
the drop across the leads should be about .9 volts. ]


After the connections were set, I sprayed them with a Urethane coating.

There is 8 gauge wire going from the jack to the panel. That's hugely oversized, but there was
a perfect length of it sitting in
the 'extras' bin at a local boatyard,
and it was a good deal. I picked it up a year ago, in anticipation of this moment.
It's good to get it out of the way.

I think the primary AC feed is a fine place to use heavier wire.

It's really weird, but the Marinco is designed to just clamp down on bare wire. This will probably be the only wiring connection on the boat that isn't sealed and heat shrinked, and I don't like it. However, to put terminal lugs on the 8 gauge wire and screw it to the jack would cause me to redesign Marinco's fitting, and I'm just
not up for it right now.


After bolting the fitting on loosely, I injected LifeSeal caulk under the gasket, and between the gasket
and the jack cover.
Using a syringe kept the mess down.

This would have been a lot easier if I'd thought of it before bolting and caulking the jack onto the boat.
Tightening the screws forced enough silicone aside to make a good connection, and the silicone should keep the marine air away from the wire. Note that this will never harden, so that the jack can be disassembled and inspected in the future.

After some thought, I went back the following weekend and removed the wires, then packed the entire inside of the jack with dielectric silicone paste.

It took nearly the entire tube.


When putting the back cover on the second time I broke it. Rather than go buy a whole new shore power plug just for that little cheap plastic cover,
I made a cover out of marine plywood. After shaping it on my bench belt sander, I smeared it with Epoxy thickened with colloidal silica to seal it and fill any gaps in the plywood.

I slapped about 6 coats of paint on it and made little matching braces that go on the inside.

After roughing up the gelcoat inside the cockpit locker (and wiping it with Acetone to remove contaminants) I screwed the interior braces to the cover.

A sheet of wax paper is between the braces and the cover, so that I don't accidentally epoxy the cover onto the boat. I just want the braces epoxied on, and the cover screws onto the braces.