On Mon, 21 May 2007 23:08:46 -0400, Wayne.B
wrote:

Let's hope that
neutral and ground are not tied together somewhere.

Well, it seems that neutral and ground are tied together somewhere on
the boat. It's not entirely clear to me what the consequences are but
in the short run it is making it really difficult to identify the
wiring.

Wayne.B brought forth on stone tablets:
On Mon, 21 May 2007 23:08:46 -0400, Wayne.B
wrote:


Let's hope that
neutral and ground are not tied together somewhere.


Well, it seems that neutral and ground are tied together somewhere on
the boat. It's not entirely clear to me what the consequences are but
in the short run it is making it really difficult to identify the
wiring.


Please make sure that you have all your AC appliances unplugged when you
are checking...

bob
s/v Eolian
Seattle

RW Salnick wrote:


Please make sure that you have all your AC appliances unplugged when you
are checking...



Also, recall Paul's point that if the
neutral and ground are switched at just
a single receptacle, then the two will
be indistinguishable everywhere.

It is difficult to offer relevant advice
since we really don't know what you are
trying to do. Is it your plan to
correctly wire all the outlets and
appliances? Are there three of these or
thirty? We still don't know if you have
an isolation transformer on board. That
kind of stuff.

Chuck


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On Tue, 22 May 2007 15:10:54 -0700, RW Salnick
wrote:

Please make sure that you have all your AC appliances unplugged when you
are checking...

I had all circuit breakers off.

Wayne.B brought forth on stone tablets:
On Tue, 22 May 2007 15:10:54 -0700, RW Salnick
wrote:


Please make sure that you have all your AC appliances unplugged when you
are checking...


I had all circuit breakers off.


That is not enough - it removes the hot side connection, but the neutral
and ground connections remain. If the appliance has a leakage path
between neutral and ground, opening the breaker will not change
anything. Unplug everything.

bob

Whatever your original project was that got you asking this question
(I would like to know that answer also), your single minded priority
now should be either

1) finding a qualified electrician to take over the original project,
or who will at the very least evaulate your boat before you next plug
back into shore power. Such an evaluation can only be successful if
you labeled all the wires as recommended in this thread, and such
qualified electrican tests your work with a meter and inspects each
area you stated you modified.

2) if your not going to do #1 above, then identifying and
disconnecting the place in the boat where nuetral and ground are
connected together and undoing must override anything else your
thinking about doing next. You cannot reliable trace the wires, and it
is commonly recognized as bad wiring practice to have them connected.

3) If even better than #2, just stop and don't do anything if you
cannot do #1. If this project does not kill you, it could kill a
future visitor to your boat if the ground protection isn't working,
could kill someone in the water near your boat while it is plugged
into shore power, and can bring with it numerous problems of stray
current to your boat or those nearby.

On Wed, 23 May 2007 07:10:11 -0700, RW Salnick
wrote:

That is not enough - it removes the hot side connection, but the neutral
and ground connections remain. If the appliance has a leakage path
between neutral and ground, opening the breaker will not change
anything. Unplug everything.

Thanks, hadn't thought of that issue, interesting. I understand your
point but unfortunately I have a *lot* of hardwired stuff that doesn't
plug in at all, or the plug is inaccessible without major disruption.

I believe that I've finally found the bus bars where all of the
neutrals and grounds terminate. They are behind a panel in the engine
room instead of being near the breaker panel where you would think.
By lifting connections circuit by circuit at the bus bars I think I'll
be able to isolate the cross connect issue, as well as being able to
identify which is ground and which is neutral. Stay tuned!

On 23 May 2007 08:19:00 -0700, b393capt
wrote:

Whatever your original project was that got you asking this question
(I would like to know that answer also), your single minded priority
now should be either

The original project was to undo some haywire installed by a previous
owner for a battery charger. I also need to run in a new circuit to
an unused breaker on the AC panel.

Whatever the cause of neutral and ground being tied together
somewhere, I suspect it has been that way for quite awhile.

I'm probably missing something but I don't see too much immediate
danger unless we end up somewhere with the shore power backwards.
That's dangerous in any case.

What are the other risks?

Wayne.B wrote:


I'm probably missing something but I don't see too much immediate
danger unless we end up somewhere with the shore power backwards.
That's dangerous in any case.

What are the other risks?


First off, I get the impression you
don't know what you're really dealing
with on that boat. I have the impression
from your posts that the wiring is not
properly identified and there is
incorrect wiring of neutral and ground.
These are not indications of a safe
electrical system and "ordinary"
prudence based on the assumption that
the boat is safely wired may not be
appropriate.

To answer your question, the main risk
is that any current in the ground wire
will cause a potential difference
between different ground points. Grab
two appliances with "grounded" cases,
one with each hand, with a potential
difference between their cases and the
risk will reveal itself to you. Do you
know that cannot happen to you on your boat?

Chuck



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On Wed, 23 May 2007 12:46:41 -0400, Wayne.B
wrote:

Whatever the cause of neutral and ground being tied together
somewhere, I suspect it has been that way for quite awhile.

The discovery process continues, thanks to everyone who has chipped in
with advice.

Here's the latest:

The AC neutral and safety ground (normally white and green) are
definitely tied together. As I understand it, this is an ABYC
standard although somewhat controversial. The AC safety ground and
the boat DC grounds appear to be totally isolated however.

I was able to buy a non-contact AC current probe at Northern Tool this
afternoon for $16. It is very useful for tracing out circuits and I'm
beginning to make some sense out of the wiring scheme by turning on
one breaker at a time.

The two bus bars that I located earlier are both for safety grounds
not neutral wires. Tomorrow I'll remove some more panels and try to
find the neutral bus. It's got to be hidden away somewhere. Checking
all of the major circuits with a current probe, there appears to be no
detectable return flow to the safety ground bus bars.