The easiest way to check for stray voltage is to disconnect your shore
power cord and connect a milliameter between the shore power ground
pin and the boats ground pin of the connector. If you get more than a
few milliamps DC current you have problems. If you check the voltage
between those two points it will probably be below .5 volts. But that
is still enough to cause current to flow.

An isolator has two back to back diodes in it and will not allow
current to flow when the DC voltage difference is below around .6
volts. That effectively breaks your ground connection for the low DC
current that causes the problems.

Regards
Gary


On 22 Apr 2004 15:09:22 -0700, (Chuck Baier)
wrote:

OK but if stray voltage entered the ground and was causing problems
for my boat or others through the shore power connections would that
not show up in my outlets on the boat. I don't have isolators as of
yet. All the tests I have run on my power cord (new) and my 110
outlets show nothing out of the ordinary. Chuck


Brian Whatcott wrote in message . ..
Here's one scenario.
The shore power distribution hardware carries a live 115 volt AC line,
a neutral line and a ground line.

As likely as not, the ground line is connected physically to the
neutral line at some closeby point. (For ALL slips)

Or if not, some misguided owner may connect his neutral lead to ground
return, with much the same effect.

This notional ground may have several volts imposed on it by the
voltage drop in the neutral return.
If you carry the ground on board to a through hull, this potential can
drive a current to the ACTUAL ground (below the water)

Brian W

On 21 Apr 2004 16:49:29 -0700, (Chuck Baier)
wrote:

Thanks for the input from everyone. One thing that is puzzling here.
Each slip is a separate home run to a meter. None of the slips are
interconnected. Each is independent. If this is the case leakage from
other bots on the ground shouldn't affect my zincs. We are looking for
a source that is outside the AC connections. At least that is what I
beleive.


"geneb321" wrote in message ...
There is an excellent article on testing for grounding problems between
shore power and boat at: http://www.yandina.com/electrolysis.htm
Gene
SV Sea Gypsy

"Chuck Baier" wrote in message
om...
Our marina has a problem at some slips with stray current. Some of the
boats are loosing zincs at a fast rate while others are not. Looking
for some help in trying to resolve this and what kind of equipment
will I need. Thanks. Chuck

In article ,
Rodney Myrvaagnes wrote:

On Wed, 21 Apr 2004 10:27:36 -0400, Jean Dufour
wrote:

Rodney Myrvaagnes wrote:

Chuck Baier wrote:

When we had the problem, we had no DC connection to the dock. We used
a trickle charger with isolation. We never have had a DC connection,
but when the ground was fixed, the zincs stopped going away.

Huh? DC to the dock? I presume you meant AC!?


No, I meant the direct coupling of the ground wire. When we used a
trickle charger it had an isolation transformer and was not grounded.
Hence, no DC connection even when there was AC.

Sorry that wasn't clear.

Careful, as some of those transformers tie the ground wire to negative
and the shielding.

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/

In article ,
Rodney Myrvaagnes wrote:

On Wed, 21 Apr 2004 10:27:36 -0400, Jean Dufour
wrote:

Rodney Myrvaagnes wrote:

Chuck Baier wrote:

When we had the problem, we had no DC connection to the dock. We used
a trickle charger with isolation. We never have had a DC connection,
but when the ground was fixed, the zincs stopped going away.

Huh? DC to the dock? I presume you meant AC!?


No, I meant the direct coupling of the ground wire. When we used a
trickle charger it had an isolation transformer and was not grounded.
Hence, no DC connection even when there was AC.

Sorry that wasn't clear.

Careful, as some of those transformers tie the ground wire to negative
and the shielding.

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/

On Tue, 27 Apr 2004 03:27:05 GMT, Jere Lull wrote:


No, I meant the direct coupling of the ground wire. When we used a
trickle charger it had an isolation transformer and was not grounded.
Hence, no DC connection even when there was AC.

Sorry that wasn't clear.

Careful, as some of those transformers tie the ground wire to negative
and the shielding.

--
Maybe so, but this one was isolated. I checked that as soon as I knew
there was a problem. It is easy to check with an ohmmeter.



Rodney Myrvaagnes Opinionated old geezer

Brutal dictators are routinely reelected by 90+%
margins. Only in a truly advanced democracy can
one win an election by a negative 600,000 votes.

On Tue, 27 Apr 2004 03:27:05 GMT, Jere Lull wrote:


No, I meant the direct coupling of the ground wire. When we used a
trickle charger it had an isolation transformer and was not grounded.
Hence, no DC connection even when there was AC.

Sorry that wasn't clear.

Careful, as some of those transformers tie the ground wire to negative
and the shielding.

--
Maybe so, but this one was isolated. I checked that as soon as I knew
there was a problem. It is easy to check with an ohmmeter.



Rodney Myrvaagnes Opinionated old geezer

Brutal dictators are routinely reelected by 90+%
margins. Only in a truly advanced democracy can
one win an election by a negative 600,000 votes.