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deniseO30 03-20-2011 04:12 PM

shore power
Last time we were at a marina and plugged into the shore power outlet (30amp) got a reverse polarity short. ii wasn't a big concern since we were only there one evening. Never got around to cking the wiring on the boat until today, over a year later :laugher

So removed the 120 volt panel and traced out wiring.(this is wiring I know about, not a mystery like some DC stuff) Oh.. what a mess, strands running under bunks, no conduit. staples on the bulkhead to light and outlet boxes, no GFIs. BUT everything checked out. no shorts anywhere that I could detect with the ohm meter. The water heater element (new WH) the 2 outlets and one reading lamp all work.

Do marinas have more problems with wet,shorted,and unreliable shore power then I expect in my limited experience?

Options to conceal wiring on bulkheads, cabin ceiling, etc? Stapling stranded house wire is not an option :D

plastic wire-mold raceways come to mind. whats the word on that? I could make it out of mahogany if there isn't a "code" on such wiring on bulkheads and other areas of the boat.
thanks in advance!

Faster 03-20-2011 04:35 PM

I thought the 'rev polarity' indication meant that the marina had the hot and neutral crossed over in their outlets....

As far as containing wires, we use this stuff linked below.. it's nice in that you can open it and add wires to it, or to trace and troubleshoot. It can be applied with hardware or double sided tape (probably not the best choice on a boat). It comes in a variety of sizes, from about 1" square to 6x6 for more industrial applications. Also, unlike tubular conduits you can exit the 'duct' anywhere you like to peel a wire out for a fixture. Raw lengths are about 6 feet.

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mitiempo 03-20-2011 04:47 PM


It would have been the marina's wiring that was wired with the hot and neutral reversed. Your panel reverse polarity light is wired between the incoming neutral and ground connections. These should not show a voltage. But if the hot and neutral incoming are reversed the reverse polarity light is then connected between hot and ground, which would measure 115 volts or so.

Classic30 03-20-2011 05:31 PM

Happens all over the world.. :(

The solution: Some boats I've seen have a simple changeover switch to swap the hot and neutral to overcome this problem.

mitiempo 03-20-2011 05:41 PM

I've yet to see that. I think it is better to fix the problem than to install a switch that can be left in the wrong position. As well, the shorepower should go to a breaker before any switches.

Sounds like a crazy Aussie fix.:D

deniseO30 03-20-2011 05:48 PM

Thanks gentlemen! I'm sure it was the Marina's power, today I only had the boat connected with the 120 volt outdoor GFI and light duty extension cord "adapted" to the shore power plug. everything worked fine, spent the rest of the day removing the stapled wires and rip.. err.. removing the wiring that was "unacceptable" (re Holmes on homes) LOL I like that polarity reversing switch idea Hartley! woo..zzzzap.. crackle. bzzzt

Basic Electricity Tutorial - Switches

Classic30 03-20-2011 08:06 PM

That's the one.. :D

It isn't really possible to leave it in the "wrong" position, since if you connect up shore power and they have it wired the wrong way around, you'll get the reverse polarity light on the AC panel and you simply switch it over.

Yes, it should be wired up after the breaker and before the sub-circuits, so you can switch on the mains, check if polarity is correct, before you turn on the sub-circuits - but there are some (like this one) that are designed to go before the breaker.

To the best of my knowledge, the worst that would happen if polarity is wrong is you'll trip the shore power breaker - probably the dockside one. I certainly don't see how anything could get fried.

The most common instance of reverse polarity I've seen is the use of home-made extension leads for shore power connection. Of course, it'd never happen to me... :o ;)

mitiempo 03-20-2011 08:23 PM

I don't think reverse polarity would trip the shorepower breaker. It certainly would if the ground was in the wrong place, as ground and neutral are connected on shore if you follow it back far enough.

The switch would work if after the main breaker.

As long as the main is a double breaker that switches both hot and neutral there shouldn't be a problem I don't think. Now if the main only switches the hot as in some older boats that could be a problem. In that case if there is reverse polarity and the switch is turned off every circuit is still hot.

deniseO30 03-21-2011 08:32 AM

I actually don't like reverse switching.. been around large motors using them... Electric Chain hoists use reverse switches

Faster 03-21-2011 08:50 AM

From a practical point of view and given (what ought to be) the rarity of a bad marina source I think a (CLEARLY MARKED) pigtail made up with reversed lines that you could insert if needed would be better... obviously a deliberate act to use that as opposed to forgetting to flip a switch....

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