I always heard you NEVER mix the AC and DC ground together. Never.

Of course, I'd like to know if this is true, but it makes a lot of sense
not to.

You guys have bumped into the "green wire controversy". Some "authorities"
say you should not connect AC and DC systems. Charles Payne is of this
opinion in his book. I'm not sure, but I think Nigel Calder also thinks its
a bad idea. On the other hand I think Dave Gerr recently had an article in
Sail or Cruising World in which he said they should be connected together.
I think this may also be the current ABYC recommendation. The rational is
that if you somehow get 110V AC into your DC system you can be electrocuted
by touching the DC if it has no earth ground. Personally I think the
chances of getting AC into my DC system are so low that I intend to leave my
systems as the original manufacturer installed them, ie. separate.

"WaIIy" wrote in message
...
On Wed, 21 Apr 2004 19:37:43 -0400, Ed wrote:

All metal (on most boats) is bonded together (green wires). This
includes the outdrives, shafts, thru-hulls etc. The bonding wire is
usually connected to ship's ground (Negative battery) and to the Green
side of the 110/220 sytem. SOMETIMES... there is a device that sits in
the middle to help save your zincs in areas with lots of current in the
water... this aside... the Ground wire on your shorepower is connected
to the bonding system.

As far as shock issues... if you touch a hot wire... or are on the swim
platform when a wave hits you and the generator... or if the plug gets
wet and you touch it (or any number of things...) you will get
shocked.... GFIs help but will not eliminate the issue.

Ed


I always heard you NEVER mix the AC and DC ground together. Never.

Of course, I'd like to know if this is true, but it makes a lot of sense
not to.

Yes, there is lots of info out there.
In my original post I mentioned Charles Payne. Actually the name is John C.
Payne and the book is "Boat Owners Electrical and Electronics Bible". He is
against connecting the two systems. This is a fairly old book though.
I checked my Nigel Calder books and he basically points out the benefits and
the problems. He concludes that you shouldn't connect the systems unless
you use a galvanic isolator or isolation transformer.
I suppose before galvanic isolators became readily available the general
consensus was to leave these two systems unconnected. Adding the isolator
and grounding the AC system to the DC system gives you some extra safety
provided the isolator and its circuit continues to function as intended so I
guess the current thinking is to go this route.

"WaIIy" wrote in message
...
On Thu, 22 Apr 2004 19:36:29 GMT, "Gordon Wedman"
wrote:

I always heard you NEVER mix the AC and DC ground together. Never.

Of course, I'd like to know if this is true, but it makes a lot of
sense
not to.

You guys have bumped into the "green wire controversy". Some
"authorities"
say you should not connect AC and DC systems. Charles Payne is of this
opinion in his book. I'm not sure, but I think Nigel Calder also thinks
its
a bad idea. On the other hand I think Dave Gerr recently had an article
in
Sail or Cruising World in which he said they should be connected
together.
I think this may also be the current ABYC recommendation. The rational
is
that if you somehow get 110V AC into your DC system you can be
electrocuted
by touching the DC if it has no earth ground. Personally I think the
chances of getting AC into my DC system are so low that I intend to leave
my
systems as the original manufacturer installed them, ie. separate.

Thanks for the info. I found a bit of stuff....

AC Ground
See Practical Sailor August 15, 1995 for a detailed treatment of the
green wire. The best solution is a heavy and expensive isolation
transformer. The acceptable solution (for the rest of us) is to install
a light and inexpensive Galvanic Isolator in the green wire, between the
shorepower cord socket on your boat, and the connection to the boat's AC
panel. Then, connect the grounding conductor (green) of the AC panel
directly to the engine negative terminal or its bus. Note that this
meets ABYC's recommendations. In choosing Galvanic Isolators, make sure
that you select one that has a continuous current rating that is at
least 135% the current rating on the circuit breaker on your dock box.
Certain Galvanic Isolators (e.g. Quicksilver) include large capacitors
in parallel with the isolation diodes, which in certain situations
theoretically provide better galvanic protection. Unfortunately, these
units cost substantially more than conventional Galvanic Isolators. If
you feel like spending real money on galvanic isolation, you might as
well do it right and buy an isolation transformer.