Wayne.B wrote in
:

Is it possible to install the isolator external to the boat using the
right combination of connectors and junction boxes?

T

Sure. Buy the 30A or 50A isolation transformer he
http://www.charlesindustries.com/main/ma_iso_bost.html

Mount it in a ventilated NMEA enclosure next to the dock power pedestal so
it can cool itself. Run a short cable from the transformer to plug into
the dock pedestal, then, with the appropriate AC twistlock outlet for the
size of the transformer mounted on the outside of the NMEA box, plug the
boat into the box....KEEPING THE BOAT GROUND DISCONNECTED FROM THE DOCK
GROUND, PLEASE!

Both sides of the isolation transformer are isolated from ground. There is
no grounded neutral like shore power uses. The only way you can be shocked
is when you are directly connected ACROSS L1 and L2 on the transformer
secondary. That's why they call it "Isolated" in the first place.

Unconnected from dock ground and the grounded nonsense of the marina and
rest of the halfass-wired boats, your galvanic current ashore is zero,
leaving only galvanic currents caused by your boat eating the zincs.

I understand how NO ground connection is better than a typical setup with an
isolator, but if the isolator is functioning, isn't the effect very close to
the same?

Let me ask it another way. If I have about 0.2 VDC across the galvanic
isolator, would I see about the same between the shore ground and
neutral/ground on the boat side of an isolation transformer?

"Larry" wrote in message
...
"Mike" wrote in news:b8idnTRka-tz-
:

(without disconnecting from shore power for 90 days :-) )?



Install an isolation transformer with an ISOLATED GROUND. That allows the
AC to flow across the transformer windings but not the galvanic current,
which is DC.....unless some idiot hooks you boat ground to the dock ground
rendering the isolation useless.

Mike wrote:
I understand how NO ground connection is better than a typical setup with an
isolator, but if the isolator is functioning, isn't the effect very close to
the same?

Let me ask it another way. If I have about 0.2 VDC across the galvanic
isolator, would I see about the same between the shore ground and
neutral/ground on the boat side of an isolation transformer?


Larry may have answered your question
indirectly.

The short answer is yes. If you follow
the recommended practice of using one of
the transformer secondary wires as a
combination neutral/ground, then you
would measure the same 0.2 volts from
there to the shore power ground.

Chuck

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On Wed, 19 Jul 2006 18:28:19 -0400, Larry wrote:

Sure. Buy the 30A or 50A isolation transformer he
http://www.charlesindustries.com/main/ma_iso_bost.html

I understand the benefits of an isolation transformer but I was
looking for lighter, cheaper, etc.

Take a fairly decent digital voltmeter and measure the voltage across
the
Galvanic Isolator with the boat hooked up and normal loads turned on.
Check
the readings when refrigerators and AC are running and drawing current.

First measure the DC voltage (reversing the leads if necessary to get
the
right polarity if the meter doesn't correct automatically). This
voltage
should measure somewhere between about 0.l volts and 1.2 volts. If it
measures exactly zero volts (less than 0.1) this indicates the isolator
is
shorted out and needs replacing. If it measures above 1.2 volts this
indicates the isolator is open circuit and needs replacing or your
ground
circuit is broken somewhere.

Second, measure the AC voltage across the isolator. This should read
0.25
or less. If it is higher than this voltage then AC current flowing
through
the isolator will be decreasing the efficiency as much as 50% depending
on
the voltage.
AC voltage can come from:-
1. on-board AC equipment that is wired incorrectly and using the ground
return instead of the neutral.
2. on-board leakage that tends to build up on older boats due to salt
deposits on electrical items.
3. (the most likely one) a neighbors boat is using the ground for the
return
instead of the neutral and this introduces AC volts back into the
ground
connection of all the other boats on that ground.

Cu-
1. One by one turn off all the AC items and see if turning one of them
off
makes the AC voltage on the isolator go away. If you find a culprit,
then
check the wiring at the point of connection and in the device itself to
make
sure it is wired correctly.

2. There is no easy way to correct accumulated leakage. You have to
bypass
the AC leakage around the isolator with a galvanic capacitor. Some
Galvanic
Isolators have a capacitor built in but they are typically just a
woefully
inadequate size so they can advertise it. You will note they never
quote
the current carrying capacity of the capacitor in their specifications.
We
make a Galvanic Capacitor rated for 5 amps AC. No others come even
close to
this capacity. You wire the capacitor in parallel with the isolator -
see
the link below.

3. Turn off the main breaker at the dock. If the isolator AC voltage
remains across the isolator then it is coming from another boat through
the
ground lead. In cases like this I've had someone watch the meter about
mid-day when no one is on board and then turn your neighbor's dock
breaker
off for a couple of minutes and then back on. (Wait at least 2 minutes
so
you are not re-starting compressors under load). If that made the AC
voltage go away, THEY are the culprit with the mis-wired boat and you
need
to report it to the marina. I've had criticism for recommending this
in the
past but the bottom line is the same thing happens in a thunderstorm
blackout and that is an act of God so the boat should be able to
survive.

If you can't get rid of the AC voltage across the isolator you need a
Galvanic Capacitor.
http://www.yandina.com/GIsolCap.html

Finally, if the DC voltage is within limits and the AC voltage is less
than
0.25 volts then it is time to consider an instrument to detect galvanic
stray current issues. Rather than purchase one and attempt to do the
measurements yourself I would suggest getting someone who has a meter
and
extensive experience in tracking galvanic currents because the meter
just
gives you a stack of voltage readings. Analysis of these readings can
take
years of experience unless there is something very obvious.

Regards,

Ann-Marie Foster,

Some observations:

Be extremely careful in measuring the
voltage across a galvanic isolator. If
the isolator should be "open", there may
be a dangerous (possibly fatal) shock
hazard between the two isolator
terminals. This is all the more critical
since you usually suspect an electrical
problem when you have to resort to
checking your isolator.

A DC voltage reading across the isolator
of zero or near-zero volts is a highly
desirable situation! It means that
galvanic (and other DC) currents passing
through the shore power ground system
are negligible, and that is always
desirable. A reading of zero volts does
not automatically mean the isolator
diodes are shorted!

Similarly for AC voltage readings of
zero or near-zero volts. A reading of
zero volts AC means there is no evidence
of appliance leakage on your boat and no
reason to suspect problems with AC
wiring on neighboring boats.

Chuck

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Larry wrote:

115 is nothing compared to watching him "finger test" 3-phase 408VAC on a
motor panel trying to figure out what it's doing.

NEVER TURN YOUR BACK ON HIM! Your ear will suffer as he touches your
earlobe with one hand in the panel with that ****-eating grin on his
face....(c;

I think I've already met him, Larry. The
ear buzzing brings back a lot of
memories. Don't see much of that anymore.

Must be the dry callouses on the fingers
that help keep the body resistance at a
high and steady level. I'd be drenched
in perspiration just thinking about it,
despite which, I've acquired a badge or
two over the years. ;-)

Chuck

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chuck wrote:

Some observations:

Be extremely careful in measuring the
voltage across a galvanic isolator. If
the isolator should be "open", there may
be a dangerous (possibly fatal) shock
hazard between the two isolator
terminals. This is all the more critical
since you usually suspect an electrical
problem when you have to resort to
checking your isolator.

Before setting the DMM to DC, set it on a higher (start at 200V) AC
setting and measure across the isolator. If it reads zero, switch it
lower until you can see a 2V AC reading. If you see a high AC voltage,
the isolator is open AND you have a dangerous fault onboard. If it reads
a couple of volts AC, the isolator is OK, but you still have a fault (or
leakage). If it reads an AC voltage no higher than the diode drop,
you're OK. The switch to DC and check for galvanic currents.

A DC voltage reading across the isolator
of zero or near-zero volts is a highly
desirable situation! It means that
galvanic (and other DC) currents passing
through the shore power ground system
are negligible, and that is always
desirable. A reading of zero volts does
not automatically mean the isolator
diodes are shorted!

Similarly for AC voltage readings of
zero or near-zero volts. A reading of
zero volts AC means there is no evidence
of appliance leakage on your boat and no
reason to suspect problems with AC
wiring on neighboring boats.

Its always a good practice to check the AC voltage of anything first.

Chuck

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--
Paul Hovnanian
------------------------------------------------------------------
Marching to a different kettle of fish.

Excellent advice, Paul!

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Chuck, in over 20 years working on boats I've never encountered a boat
in the water on shore power that had zero volts across the Galvanic
Isolator. Just the zincs on your underwater metal will introduce about
0.5 volts DC. Getting a voltage reading does not in itself indicate
electrolysis unless it is over about 1.1 volts since that is the
purpose of the GI to block DC current from sources up to about 1.2
volts.

So a reading of zero is a fairly good indication that either the GI is
shorted internally or more likely there is another connection somewhere
on the boat that is by-passing the GI and rendering it inoperative.
One source to watch is the television cable if you have one. The
shield on this will probably be grounded at the dock end and depending
on how it couples to your TV or cable box it can easily be grounded at
the boat end too. This shorts out or bypasses the GI and voids the
electrolysis protection.

However you are correct that an AC reading of zero is a good indication
that there is no AC leakage.

Regards,

Ann-Marie Foster,




chuck wrote:
Some observations:

SNIP
A DC voltage reading across the isolator
of zero or near-zero volts is a highly
desirable situation! It means that
galvanic (and other DC) currents passing
through the shore power ground system
are negligible, and that is always
desirable. A reading of zero volts does
not automatically mean the isolator
diodes are shorted!

Similarly for AC voltage readings of
zero or near-zero volts. A reading of
zero volts AC means there is no evidence
of appliance leakage on your boat and no
reason to suspect problems with AC
wiring on neighboring boats.

Chuck