AC Mystery

[karista]

Having heard of AC problems on a friend Catalina, I checked out my AC, using a Circuit tester (with the little lights) all outlets checked out correct. Also the GFCI green light showed it was operating correctly in addition the panel green light showed correct shorepower input. OK, I was happy , but just to be sure, I put on my voltmeter and it showed 120V between hot and neutral but also 120V between hot and ground, and 0 voltage between ground and neutral. Now, unless I am mistaken I should not have a voltage reading between hot and ground. So why is the circuit tester showing everything correct? Also any ideas how to "quickly" isolate?? The wiring diagram that came with the boat is pretty useless as it does not match the wire colors on my boat (Shows black but is red, etc) and is incorrect in several callouts,  I am the original owner and have not changed the AC wiring.

[Ted Pounds]

You are mistaken.  You should definitely have a voltage between hot and ground.  Otherwise hot would be shorted to ground  (or it wouldn't be 'hot').  Your wiring is OK.

Ted Pounds
B.S., Electrical Engineering, MIT class of '79

[karista]

Ted
Thanks for the reply! Can you tell me whether the DC ground and AC ground are connected somewhere in the boats wiring.
My AC ground is definitely connected somewhere to the boats DC ground. I disconnected the shorepower AC ground to check this and my meter still showed a AC ground reading. I further checked this be checking continuity from the shorepower boat receptacle ground to the engine ground and it continuity.

[BillG]

The infamous" Green Wire Controversy", these sites may answer your question.
http://www.boatus.com/boattech/Casey/36.htm
http://www.practical-sailor.com/newspics/charts/905greenwire.pdf

[Craig Illman]

That's why galvanic isolators or isolation transformers are a good idea. So a voltage leak coming from somewhere else in the marina on the AC ground won't erode your zincs or electrocute a person nearby in the water.

Craig

[karista]

Craig
I installed a Galvanic Isolator about 6 months ago and have found no improvements in Zinc replacement time. Here in the warm Gulf waters I have to replace the Zinc every 4-5 months. I thought the Isolator would help, but I see no difference. I tried to check my ground wiring and now have discovered that one of green wires on the AC ground connector panel is wired to the boats DC ground. This must be the standard Catalina set-up as this wiring is factory original. The Galvanic isolator is wired into the incoming AC ground wire which then goes to the AC panel connection.

[Craig Illman]

Have you checked continuity between the shore-side ground side of the isolator and the boat dc ground?  I don't think it will eliminate the current flow, but limit it. There's other reasons for zincs to corrode. I just put an isolator on a few months ago, so I don't have much of a history and my dock still may be pretty "hot". A transformer ($$$$) certainly would have been preferred.

Craig

[Ted Pounds]

Yes the AC and DC grounds are connected.  That's to prevent electrocution if there's an AC fault to the DC system. 

Karista, I'm in freshwater but I think 4 - 5 months is normal for zincs in salt water.  What do you saltwater sailors think?

[karista]

Ted
Yes, 4-5 months is normal for salt water, however this is precisely the reason why I installed a Galvanic Isolator, hoping that it would extend the lenght. It has not! For $180 I could have bought a lot of 1" zincs.

[Mike and Joanne Stimmler]

I've heard that some water heater companies require that you have a galvanic isolator for their warranties to be in effect. Any ideas on why?

[Ken Juul]

Zinc's only lasting a few months, is that normal in salt water? It's news to me.  Perhaps my location mid Chesapeake makes the water more brackish than salty. (but is sure tastes salty when in it!)  Luna Loca is in the water 11 months a year, I change my shaft zinc every sping haul out, but my estimation is it is only slightly worn.   I may be lucky, most of the boats surrounding me are either almost new with transformers or maintaing their batteries with solar so perhaps the water is free from too many stray currents.

[karista]

Ken
Before sailing the boat down to St. Petersburg, Fl, she was located in Deale, Md, which is approx 15 miles south of Annapolis. While there I could easily go well over a year w/o changing the zinc. I believe the water in the mid Chesapeake is more fresh than salt, as I also basically had no barnacle problems there.

[Ken Juul]

Karista thanks.  Were in Deltaville.  Heading to Annapolis next week, may spend a night in Herrington Harbor.  When I was boat shopping had a friend that worked for Clipper Bay Yachts.  Spent quite a few afternoons after an unsuccessful boat search drowning my sorrows  in that little outside eatery just south of the bridge.