Obviously, that second feed needs to go through AN isolator, but I'm not sure you can use the same one.

Calling all elevtron heads: Help!


Jeff

Joe & Bill,
I'm not sure about the circuitry of the isolator, Doug can most likely help there. I feel there is a problem on either your boat or with the shore power. 1st thing is to eliminate your boat. Check to be certain that in the Air Conditioner circuits on board, the netural, white wire is not grounded to the hull or green conductor. If not on board then could be power cord or shore power. Swap cords to check out cords. Swap plugs on dock to check shore power.

Roger

I was studying the owners manual schematic for the 12DC system last week and I also took a quick look at the 120AC schematic. It shows the optional 2nd 120V supply. I'll check after work and see how that 2nd supply is tied into the rest of the boat.

-Karl

Under no circumstances connect the neutral (white) wire from the shorepower directly to the hull.

The stock galvanic isolator is probably a 30 amp unit - mine is and same for other correspondents. It is rated for the largest breaker in the circuit, since a short from hot to hull will pull a breaker.

I am not sure it is a good idea to connect the neutral (white) wires from two different shore power feeds together. There could well be some voltage between the two. And it is a bad idea to allow current from one hot to return through another neutral. I have no experience trying this, but it is a bad idea because it relies on the marina to provide a clean pair of neutrals and my experience has been to trust nothing to the marina.

My website (http://geocities.com/dougmrose/) shows, under Generic Marinette Wiring, the best information I have on how Marinettes were wired. Note that the double-ac diagram shows the neutrals tied together, in violation of what I just said. I would not do it, I would buy another 30-amp galvanic isolator for the second circuit. I have put a number of comments in red - this isn't the only thing I would change from the original.

All I can advise is to evaluate my reasoning and decide - and remember there is at least one actual professional electrician on this site, and we should hear from him....

Life (and boating) is never simple!

Jeff

Re-reading my post from last night, I realize that I wasn't making any sense. The green wire goes to the galvanic isolator, of course, and it is likely to be the same connection at the dock. I guess there would not be a problem connecting two greens together unless you were plugged into two different boxes on two different circuits. But again, that depends on the marina wiring...

The power to the dock is likely red-black-white-green, with red a 120 vac feed, black being an out-of-phase feed so that there is 240 vac from red to black, white being neutral, and green being the ground.

Often, there are two 30-amp twistlock connectors side-by-side at the dock, wired with the red on one and the black on the other. If you plug into both with a Y-adapter, you can get 240 vac for larger loads. This makes more sense than a second 120 vac feed but Marinettes are not wired for it, and I believe would blow the breakers if you hooked two 120 vac plugs like the schematic, but I don't have such a setup so I don't really know.

At my marina, the dock receptacles are always going bad from corrosion. So folks wander around, plug in hand, looking for one that works. As it happens, the two sides of the dock are on different circuits, and this could cause problems with the factory Marinette wiring for two plugs.

My 32 has two shore power inputs and both green wires are tied together entering the galvanic isolator. No problems after 12 years.

Rick,
Sounds like you've got the answer.

Is you isolator a Quicksilver, possibly like the one on my boat? If so, do you know the amperage rating?


Thanks, Joe

If there is a second shore power, then I would use it only to run the air conditioner, and not interconnect it with anything else. It would also be possible to run the hot water heater on it, perhaps. A 20,000 BTU unit will draw perhaps 15 or 18 amps and so will work well on a 30 amp breaker despite the starting load. This has been suggested already on this site but I don't remember where...

I would not connect the green for this circuit to the existing galvanic isolator, because there is no guarantee that this green is at the same potential as the green for the other circuit. Someone else's short circuit might flow in one green and out the other to find an easier path back to the power company. If your AC frame is not connected to the hull, I would simply connect it to that. Otherwise, I would buy another isolator.

I have an isolation transformer with four windings. This allows a choice of power input and output. This is a great way to go but I got it surplus and I have no idea where to get another one.

I see that a suitable 3.8 KVA isolation transformer, with 4 110 v coils, is about $600. This is the best of all worlds: no ground connection to the shore, either 110 or 220 volts in, and both 110 and 220 volts out. You can run each half of your ac panel from a winding, get 220 volts for the air conditioning and hot water, and be able to plug in anywhere. I bought mine for its scrap value, I think it was $15.

http://www.defender.com/...%7C1212797&id=614209