"Glenn Ashmore" wrote in news:l_2kg.112247$Ce1.77235
@dukeread01:

http://www.bluesea.com/Article_detai..._ID=290&id=299

What this manufacturer of diode isolators DOESN'T tell you is that their
product does NOT protect your underwater metal parts from AC LEAKAGE
caused by connecting this wire.

These "isolators" are simply two rows of silicon diodes in series with
the boat's ground wire. Like this:

|--|-|-|-------|
ac gnd--| |----boat gnd
|--|-|-|-------|

Each diode has a forward breakover voltage of around .6V. By having two
rows in parallel, either a positive or negative voltage over, in my
example, 1.8V (AC or DC it matters not) across the device will make it
conduct. 120VAC will make one row conduct on one half cycle, the other
on the other half cycle, a virtual short if there is any kind of short OR
AC LEAKAGE in any appliance. Any leakage that will trip a GFCI, for
instance, will make this device ALWAYS conduct, rendering it useless, a
fact Blue Sea will never tell you, of course. Once it is conducting the
AC leakage current from the hot water heater's leaky element to the
grounded cabinet of the hot water heater, all the DC electrolysis
currents it blocked destroying your prop and zincs now pass through it as
if it never existed. The AC current through it provide the breakover
voltage that was supposed to block the electrolysis currents...either
way.

The solution to THIS malady is an isolation transformer of sufficient
power to isolate the boat without overheating, itself. Big yachts have
them in the bilge. They're beasts humming away in my bud's Hat 56 FBMY.
The only connection between the power company and a boat protected by an
isolation transformer is magnetic power in the core. NO DC current can
pass between the windings, at all, even if the hot water heater leaks
like a sieve.

By the way, if the boat had had an isolation transformer, the only way
the kids would have gotten shocked is if TWO appliances connected to the
water had a short on L1 on one of them and L2 on the other. The whole AC
power system on the secondary of the isolation transformer has NO PATH to
earth. The only way you can get shocked is if you get right across the
AC power leads, L1 to L2. Too bad the whole power grid doesn't simply
have NEUTRAL isolated from ground, making it impossible to get a shock by
touching one of the wires and ground.

Larry wrote:
"Glenn Ashmore" wrote in news:l_2kg.112247$Ce1.77235
@dukeread01:

http://www.bluesea.com/Article_detai..._ID=290&id=299

What this manufacturer of diode isolators DOESN'T tell you is that their
product does NOT protect your underwater metal parts from AC LEAKAGE
caused by connecting this wire.

These "isolators" are simply two rows of silicon diodes in series with
the boat's ground wire. Like this:

|--|-|-|-------|
ac gnd--| |----boat gnd
|--|-|-|-------|

Each diode has a forward breakover voltage of around .6V. By having two
rows in parallel, either a positive or negative voltage over, in my
example, 1.8V (AC or DC it matters not) across the device will make it
conduct. 120VAC will make one row conduct on one half cycle, the other
on the other half cycle, a virtual short if there is any kind of short OR
AC LEAKAGE in any appliance. Any leakage that will trip a GFCI, for
instance, will make this device ALWAYS conduct, rendering it useless, a
fact Blue Sea will never tell you, of course. Once it is conducting the
AC leakage current from the hot water heater's leaky element to the
grounded cabinet of the hot water heater, all the DC electrolysis
currents it blocked destroying your prop and zincs now pass through it as
if it never existed. The AC current through it provide the breakover
voltage that was supposed to block the electrolysis currents...either
way.


GFCI protection at the pedestal of the neighboring
boat causing the problem would have prevented the
problem at the source if it were a 125 volt circuit.

The solution to THIS malady is an isolation transformer of sufficient
power to isolate the boat without overheating, itself. Big yachts have
them in the bilge. They're beasts humming away in my bud's Hat 56 FBMY.
The only connection between the power company and a boat protected by an
isolation transformer is magnetic power in the core. NO DC current can
pass between the windings, at all, even if the hot water heater leaks
like a sieve.

By the way, if the boat had had an isolation transformer, the only way
the kids would have gotten shocked is if TWO appliances connected to the
water had a short on L1 on one of them and L2 on the other. The whole AC
power system on the secondary of the isolation transformer has NO PATH to
earth. The only way you can get shocked is if you get right across the
AC power leads, L1 to L2. Too bad the whole power grid doesn't simply
have NEUTRAL isolated from ground, making it impossible to get a shock by
touching one of the wires and ground.


ABYC and common sense would have you ground the
neutral of the isolation transformer secondary and
use that as your equipment grounding conductor.
That way you remain isolated from the AC systems
of the rest of the world, but you maintain the
safety benefit of equipment grounding. Even GFCI
protection on the secondary wouldn't work without
that ground. You don't need the green wire for
GFCI to detect a ground fault, but you DO need a
connection to "ground" for a ground fault to
occur. So if you leave off a secondary ground, you
prevent ground faults by allowing the hot wire to
short to an equipment cabinet undetected! Not
likely to be very popular, Larry.


Chuck

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chuck wrote in news:1150376821_9981
@sp6iad.superfeed.net:

ABYC and common sense would have you ground the
neutral of the isolation transformer secondary and
use that as your equipment grounding conductor.
That way you remain isolated from the AC systems
of the rest of the world, but you maintain the
safety benefit of equipment grounding. Even GFCI
protection on the secondary wouldn't work without
that ground. You don't need the green wire for
GFCI to detect a ground fault, but you DO need a
connection to "ground" for a ground fault to
occur. So if you leave off a secondary ground, you
prevent ground faults by allowing the hot wire to
short to an equipment cabinet undetected! Not
likely to be very popular, Larry.



If the equipment on my bench is plugged into my fully isolated isolation
transformer, touching either (BUT NOT BOTH) sides of the line is no shock
hazard whatsoever, the very reason for the isolation transformer in the
first place. No equipment ground is necessary.

"Ground" is just a point, a reference, that's way overrated....and
misunderstood. Voltage never killed anyone...Voltage DIFFERENCE does.

I looked for a video I had on my old computer that was posted from a
power company. The subject of the video was the guys who fly around very
high voltage transmission lines in a helicopter, drop off a man hanging
from that line, to replaces some of the gear on the hot end of
insulators, FROM the hot end of insulators you can only get near if you
are already at that potential, several hundred thousand volts above
"ground". The most impressive part of the video is the guy sitting on
the little platform beside the helicopter's skids with a buzz stick in
his hands sticking out as they approached the line. The high voltage
reaches out 10's of feet in a fairly amazing arc to the end of the buzz
stick until the helo gets close enough to actually attach the helo's
chassis to the high tension power line, putting them both at several
hundred thousand volts off "ground" so men and parts can be transferred
as the expert pilot holds the helo rock still against the line.

Sorry I can't find it in the stacks of CDRs and DVDs piled around here.
It was a great movie to watch. JUST DON'T TOUCH GROUND WHILE YOU'RE OUT
THERE AND YOU'RE FINE!...(c;

It's all about your "reference"....

Larry wrote:
chuck wrote in news:1150376821_9981
@sp6iad.superfeed.net:

ABYC and common sense would have you ground the
neutral of the isolation transformer secondary and
use that as your equipment grounding conductor.
That way you remain isolated from the AC systems
of the rest of the world, but you maintain the
safety benefit of equipment grounding. Even GFCI
protection on the secondary wouldn't work without
that ground. You don't need the green wire for
GFCI to detect a ground fault, but you DO need a
connection to "ground" for a ground fault to
occur. So if you leave off a secondary ground, you
prevent ground faults by allowing the hot wire to
short to an equipment cabinet undetected! Not
likely to be very popular, Larry.



If the equipment on my bench is plugged into my fully isolated isolation
transformer, touching either (BUT NOT BOTH) sides of the line is no shock
hazard whatsoever, the very reason for the isolation transformer in the
first place. No equipment ground is necessary.


The isolation transformer on my bench provides an
equipment grounding conductor on the secondary
side and also the ability to measure leakage current.


"Ground" is just a point, a reference, that's way overrated....and
misunderstood. Voltage never killed anyone...Voltage DIFFERENCE does.

I looked for a video I had on my old computer that was posted from a
power company. The subject of the video was the guys who fly around very
high voltage transmission lines in a helicopter, drop off a man hanging
from that line, to replaces some of the gear on the hot end of
insulators, FROM the hot end of insulators you can only get near if you
are already at that potential, several hundred thousand volts above
"ground". The most impressive part of the video is the guy sitting on
the little platform beside the helicopter's skids with a buzz stick in
his hands sticking out as they approached the line. The high voltage
reaches out 10's of feet in a fairly amazing arc to the end of the buzz
stick until the helo gets close enough to actually attach the helo's
chassis to the high tension power line, putting them both at several
hundred thousand volts off "ground" so men and parts can be transferred
as the expert pilot holds the helo rock still against the line.

Sorry I can't find it in the stacks of CDRs and DVDs piled around here.
It was a great movie to watch. JUST DON'T TOUCH GROUND WHILE YOU'RE OUT
THERE AND YOU'RE FINE!...(c;

It's all about your "reference"....


Just a few last comments.

Basically the world doesn't like the idea of hot
wires shorted to our equipment cases. But worse
than that, they don't like for it to happen
without some thing alerting us to the problem or
correcting it.

With your two-wire, groundless system, I know of
no way to detect and/or clear such a short. Your
proposed system effectively says: leaks happen.
Don't ask and don't tell. We've tossed the
equipment grounding conductor and now we're free
and safe.

But as I have said, GFCI will not work with your
system if there is no "ground". Yes, yes, the
device doesn't actually require a connection to
the equipment grounding conductor to work. But
there must be a ground for a ground fault to
occur! Otherwise there is no differential current
for the GFCI to detect.

Actually it is sometimes difficult to avoid
grounding an appliance case. Then what? What about
lightning protection?

I understand that you're making the point that the
use of grounding and bonding per the NEC is
sometimes the cause of problems. But the system is
what we have, and it prevents an awful lot more
electrical injuries than it causes.

Chuck

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I agree with Chuck on grounding. Only an idiot would NOT ground the AC
systems to other items on the boat. As an example suppose your hot
water heater developed an AC short to its case. You are standing in the
bilge hanging across the engine to reach the thing to work on it. The
engine is at ground via the shaft etc. If the water heater is not
bonded to the engine ground you get zapped!
This is only one example of what will happen if you don't have things
tied together on a boat. It is next to impossible to insure that there
will be no AC leakage in any piece of equipment especially in the
marine environment.

Even the boats that try to maintain isolated underwater (thru hull
etc.) items are a risk. As long as the items maintain isolation it
works ok but as soon as some worker comes aboard and "fixes something"
the chances of the isolation remaining drops.

The only cure for the galvanic problem is an isolator or better yet the
isolation transformer.

Testing to see if you have any faults with an ohmmeter to the marinas
ground pin on the shore cable is futile. There will usually be several
millivolts of voltage above ground on the shore power ground pin and
some DC offset voltage that will immediately invalidate your ohmmeter
reading.

Measuring for DC current between the shore ground and the boat ground
will tell you if there is a galvanic problem.

Regards
Gary

There is a solution to the degraded performance of galvanic isolators
in the presence of AC leakage. See the article at
http://www.yandina.com/GIsolCap.html

Larry wrote:
wrote in news:1150426885.033779.258180
@g10g2000cwb.googlegroups.com:

If the water heater is not
bonded to the engine ground you get zapped!


(click!) The GFCI just trips. Noone gets zapped.

Another case to make dock GFCIs MANDATORY at all marinas.


If the water heater is on a 250/125 volt
circuit there can be no GFCI.

Do you see a lot of water heaters
operating at 125 volts?

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chuck wrote:
Larry wrote:

wrote in news:1150426885.033779.258180
@g10g2000cwb.googlegroups.com:

If the water heater is not
bonded to the engine ground you get zapped!


(click!) The GFCI just trips. Noone gets zapped.

Another case to make dock GFCIs MANDATORY at all marinas.


If the water heater is on a 250/125 volt circuit there can be no GFCI.

Do you see a lot of water heaters operating at 125 volts?

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There are a lot of 6 to 12 gallon hot 125 volt water heaters on sailboats.
krj

When I asked my original question, I had no idea that there is no
apparent consensus on how to wire a boat for safety and for galvanic
corrosion protection. Maybe those are mutually exclusive. Not being an
electrical engineer, or electrician, just a long-time boat owner, I
would not know which of all these conflicting replys to trust. And a
search of Boat.us and the ABYC also indicates more confusion. Is there
no governing body, such as UL, with a scientific, well reasoned
approach? What about brand new quality boats? How does Viking, Hatteras
or Cabo do it? All three of those manufacturers are lauded for their
wiring systems installations.
Russell
krj wrote:
chuck wrote:
Larry wrote:

wrote in news:1150426885.033779.258180
@g10g2000cwb.googlegroups.com:

If the water heater is not
bonded to the engine ground you get zapped!


(click!) The GFCI just trips. Noone gets zapped.

Another case to make dock GFCIs MANDATORY at all marinas.


If the water heater is on a 250/125 volt circuit there can be no GFCI.

Do you see a lot of water heaters operating at 125 volts?

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There are a lot of 6 to 12 gallon hot 125 volt water heaters on sailboats.
krj

Russell wrote:
When I asked my original question, I had no idea that there is no
apparent consensus on how to wire a boat for safety and for galvanic
corrosion protection. Maybe those are mutually exclusive. Not being an
electrical engineer, or electrician, just a long-time boat owner, I
would not know which of all these conflicting replys to trust. And a
search of Boat.us and the ABYC also indicates more confusion. Is there
no governing body, such as UL, with a scientific, well reasoned
approach? What about brand new quality boats? How does Viking, Hatteras
or Cabo do it? All three of those manufacturers are lauded for their
wiring systems installations.
Russell
krj wrote:
chuck wrote:
Larry wrote:

wrote in news:1150426885.033779.258180
@g10g2000cwb.googlegroups.com:

If the water heater is not
bonded to the engine ground you get zapped!

(click!) The GFCI just trips. Noone gets zapped.

Another case to make dock GFCIs MANDATORY at all marinas.

If the water heater is on a 250/125 volt circuit there can be no GFCI.

Do you see a lot of water heaters operating at 125 volts?

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There are a lot of 6 to 12 gallon hot 125 volt water heaters on sailboats.
krj


I think if you follow ABYC standards,
you will be squarely in the mainstream
of boat wiring. Many insurance companies
require ABYC compliance. Many marine
surveyors inspect of ABYC compliance.
The key books covering marine
electronics (by Calder and Wing, for
example) are based on ABYC standards.
They both discuss safety and corrosion
issues. One could do worse than reading
the relevant chapters of these books. It
would surprise me to find any
significant discrepancy between ABYC
standards and various tips and how-to
literature available at WM and BoatUS.

The NEC is a pretty iron-clad set of
standards and should guide us as far as
it goes. However, it doesn't contemplate
boats actually floating on the water and
so is silent about some things. The
philosophy, however is very robust.

Many of the posters enjoy challenging
some of the sacred cows from time to
time, but I think they're all supportive
of accepted standards at the end of the
day. (Just my opinion, of course)

What is not always covered adequately in
the standards is defensive strategies to
protect you from non-complying nearby
boats.

Good luck, Russell.

Chuck

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