On Thu, 24 May 2007 19:11:33 -0700, Peter Bennett
wrote:

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.

NO! ABYC, CSA and probably other standards require that the shore
power neutral (white) and the safety ground (green) MUST NOT be
connected on board. (They will be connected somewhere ashore.)

OK, Peter and Dan, you are both being very helpful, thanks. Please
bear with me for one or two more iteration levels into my
understanding.

Here's the situation: The boat has two 120 volt, 50 amp AC legs,180
degrees out of phase with a neutral wire circuit in the middle similar
to house wiring. Each 50 amp leg can be isolated with its own double
pole breaker. All three wires (hot-neutral-hot) are easily
accessible.

I went out today and bought a digital clamp on ammeter. My theory is
that if I have leakage through a ground path, it should show up as a
current imbalance between the hot wire and neutral wire, similar to
the logic in a GFI.

So here is my next stupid question, sorry. If one of the loads has
the safety ground and neutral wire inadvertantly reversed, it seems to
me that this should show up as a current imbalance as I previously
outlined. In your opinion, is this a valid test for that condition?

If so, my next plan is to test every circuit and load, one at a time,
to make sure that nothing was haywired in the past, and that nothing
is leaking current to ground.

Stupid question number 2. I believe that if I have two equal
resistive loads, one on each leg, that the net neutral wire current
should read zero. Can you verify if that assumption is correct?