stray voltage?

[victoria28]

Hi, 1992 Catalina #246 - I am installing a replacement Seaward 6 gal tank. While
using my multimeter to check the existing wiring to ensure that the power was
off prior to hook up I noticed that while there was no reading between black and
white, or black and green, I did get a reading between white and green - it
quickly fluctuated back and forth from 0.1V to as high as 1.2V.
Any ideas what is going on here? is this a problem? I have decided to not
proceed with the hookup until I feel confident about this.
Thanks

[mitiempo]

Easiest way to ensure the power is off is to unplug from shore power. If you were still plugged in do you have a double pole breaker (that you turned off) that breaks both hot and neutral? I don't play with AC unless I know the boat intimately (mine) so I always unplug the shorepower cable. I've seen AC that bypassed the panel on occasion. If you were totally unplugged from the dock I'd have to check a bit to see where everything goes and why you're getting a reading when you shouldn't. What does the AC have to do with a Seaward tank?

[hellosailor]

In a perfect world the green (ground) and white (so-called neutral) would both be at ground level but AC wiring usually isn't perfect. Two concerns: Why they are different, and why it is fluctuating.

I wouldn't call it "don't sleep tonight" dangerous, but it could mean a galvanic problem so either way you'd want to look into it. On boats, miswiring of chargers and generators is a good way to have green/white problems. You should be able to dig up a number of detailed threads about the problems on this and other boating forums.

Odds are that however this affects your tank installation--you can finish that, the AC troubleshooting will be somewhat more extensive and separate from the tank.

[mitiempo]

If the AC was either off (double pole breaker) or unplugged it has to be a DC leak through the common ground I think.

[Architeuthis]

Originally Posted by victoria28

... While using my multimeter to check the existing wiring to ensure that the power was off prior to hook up I noticed that while

there was no reading between black and white, or black and green,

I did get a reading between white and green -

it quickly fluctuated back and forth from 0.1V to as high as 1.2V.
Any ideas what is going on here? is this a problem? I have decided to not
proceed with the hookup until I feel confident about this.
Thanks

With boat wiring almost nothing can be taken for granted.

Is this an AC circuit? (I guessing yes but...) I suspect the jumping around could be the result of a frequency other than 60hz (meter may not like that). Some meters will measure the frequency (which can often say alot).

If it is the AC only then white is neutral and green is ground (just being clear). These circuits are not broken when breakers are opened (agian a reminder to me and being clear).

Unplug boat, measure voltage between green and white, record both voltage and frequency or record voltage when using AC voltage setting and DC voltage setting (be sure to use correct voltage setting for meter so you do not measure a 120volt circuit with 12 volt meter setting)

If voltage is zero with cord unplugged, but 0.1 to 1.2vac when plugged in then you have traced it down to just the AC circuit. Under idea conditions the voltage between these two points is zero but really they are not.

The only point at which they should be connected is back in the panel in your house (or close to the ground point for the AC system on shore) but really there are lots of other little connections (wet plugs for example) and inductive coupling.

If this was my boat and I had normal zinc use and everything worked fine, I would likely ignore it. If it was a customers boat I would start checking to be sure everything was clean and dry and the isolation system was working properly, ect ect then I'd say it was a shore problem.

Kinda hard to say it is a problem, depends on so many things, like zinc use. I expect that the DC negative is well grounded to the AC ground....and so on.

Another boat in the marina can cause this (voltage between neutral and ground) so sometimes shutting off power via breakers can give more info.

Thats all off the top of my head at this point.

[btrayfors]

Originally Posted by Architeuthis

With boat wiring almost nothing can be taken for granted.

If it is the AC only then white is neutral and green is ground (just being clear). These circuits are not broken when breakers are opened (agian a reminder to me and being clear). .........

Uhhh.....on AC circuits on a boat both the hot (black) and the neutral (white) should also be switched thru a double breaker. Only the ground (green) is unswitched, and it should ONLY be grounded at the source (shore power, generator, or inverter).

Sure is true, though, that on a boat NOTHING can be taken for granted.

Bill

[hellosailor]

"If it is the AC only then white is neutral and green is ground (just being clear). These circuits are not broken when breakers are opened (agian a reminder to me and being clear). "

As Bill notes, on a conventional [read: legal and built to codes] boat AC installation, the AC will come into a dual main breaker. That is installed to cut both the black and white (hot and neutral, but that's just "hot and hot" on my planet) lines and if either one trips, BOTH TRIP because they are physically pinned together.

Since neutral is just "hot by another name" there's no other safe way to do it.