chiropaul23@yahoo.com writes:

Paul,

This is an area that requires more than a casual knowledge of electricity. I
would highly recommend that you run over to Amazon and buy two books: Charlie
Wing's "Boatowner's Illustrated Electrical Handbook", and Nigel Calder's
"Boatowner's Mechanical and Electrical Manual". They cover in detail what you
need.

As for the ground, this is exactly what you need an isolator for. You should
use a 30 amp isolation transformer, and connect the ground on the output side
to the 12 volt ships (DC) ground. The incoming AC ground (green wire) goes to
the input of the transformer. It's critical that the incoming AC ground is
kept isolated from the ship's DC ground, especially on a wooden boat.

Scott Welch
FirstClass Product Manager
www.firstclass.com

"Things turn out best for people who make the best of the way things turn
out." - John Wooden

A bit of clarification here -  ABYC E-11.17 requires that the safety ground (green wire) of the
AC system ON THE BOAT be bonded to the "engine negative terminal or its bus". However, to
prevent galvanic corrosion, a galvanic isolator OR an isolation transformer is also needed.
While an isolation transformer is an excellent way to provide the isolation, they are big, heavy
and expensive. As such, the galvanic isolator that Paul proposed should be just fine for his
application.

If the boat uses a shore power system as used by many trawlers under 40' and as Paul described
(i.e., 30A, 120V, no isolation transformer, with a galvanic isolator), the green wire on the
boat side of the isolator MUST be bonded to the DC ground/engine block (see:
http://www.yandina.com/acrobats/GalvOwnManual.pdf).

An alternate way of complying with the requirements if you have the space and budget to do so,
is to add an isolation transformer to the circuit (see:
http://www.victronenergy.com/upload/documents/Datasheet-UK-Isolationtransformer.pdf). This
transformer sits between the shore power inlet and the main AC panel. The safety ground (green
wire) is galvanicly isolated from the shore safety ground, but the boat side green wire still
gets bonded to the DC ground system.

Kevin

----- Original Message -----
From: "KevinR"

REPLY
In my work  I have seen a few wooden boats nearly destroyed  because they
were wired to conform to ABYC standards.  What most people do not  recognize
is that  the standards was written to prevent shock hazard to people and
sacrificing the boat was considered acceptable.
The intent of the standard is to GROUND  the AC electrical system because
all the protection  like GFCI and circuit breakers rely on the current path
provided by the green ground wire.  Bonding the engine block  is a
convenience short cut.  This method is a quick way to connect to a large
metal mass  in direct contact with  the sea water. But if a driver saver
disk is installed in the shaft coupling then you hav ebroken this path to
ground.  some of the newer  engines are now deisgned not to have the block
as a DC current carrying  conductor in the start circuit. The end result  is
an engine that is still isolated.  this negates the intent of th eABYC
standad.

In wooden boats docked in waters  known to have stray current from shore
power facilities  it is common to see  this current passing in ( via thru
hul fitting) through one side of the hull;  follow the bonding wires and
exit the hull on the other side  which is closer to the land mounted
transformer. this will happen even if both a galvanic isolator or an
isolating transformer is used as long as th efitings are bonded per ABYC.
Not good!.
The wood around the thru hulls will soften as the lignin is destroyed by the
passing current.

ABYC  standards were originally formulated for non conducting plastic boats.
ABYC came into existence after the heyday of wooden boats had passed.  I
doubt the technical committees  really gave much thought to the issue. Their
focus was  people safety and shock prevention.
You can be compliant  to the standard and still get away  from  running
bonding wires to every thru hull fiting.  You need a separate ground plate
of approximately  one square yard or meter.  This will securely  ground the
AC electrical system  If the boat is fitted with an inverter some additional
wiring tricks  for the neutrals  and the green wire bonding bus  must be
observed.

cheers
Arild