Larry wrote:
chuck wrote in news:haikf.8489$N45.4470
@newsread1.news.atl.earthlink.net:


providing an opportunity for a
potential difference between your DC ground system and the grounded

case

of an AC appliance. An improperly wired boat in the next slip can cause
real safety problems aboard you vessel.



Show me how. The water is earth ground, no matter how the joker's boat
is wired next door. If he's wired wrong, the AC current through the
water will trip the AC breaker on the dock. Try it.


Well, the classic example of this is when the guy on the boat next to
yours uses a 2-wire AC cord on an automotive-type battery charger. The
charger develops leakage between the hot AC wire and the 12 volt DC
ground. Won't trip any breakers because the current is too small. The
circuit could easily deliver 10 amps forever with nothing tripping.
Remember that the breakers are sized to trip before the wire causes a
fire; NOT before enough current has passed through a person to cause
electrocution. We're not talking about someone savy enough to use GFCI
outlets here which can detect small current leakages.

Alternatively, an automotive-type charger is plugged into a makeshift
extension cord with the hot and neutral wires swapped. No green wire at
all. Even without a leakage or short, the hot AC wire is now connected
directly to the neighbor's DC ground system to his propeller. Again,
nothing trips because the path through the water to the AC system's
ground/neutral junction is too high a resistance to carry 15 amps (or
whatever the breaker is rated at) with 120 volts applied.

Next, you grab your engine with one hand and open the door of your
fridge with the other as you reach for a cold one and you receive an
unhealthy dose of 60 Hz.


There is NO WAY for the guy's boat next door to raise the AC potential of
the whole ocean up off the AC shore ground potential my fridge is
connected to! He'd need a thousand amp breaker to raise it a tiny
fraction. The shore power ground is hooked to the earth/seawater.


What happens, Larry, is that your fridge cabinet is connected to the
green equipment grounding conductor and to an AC ground/neutral junction
on land. Your engine is connected through the water to the hot AC wire
on the neighboring boat. The voltage between those two pieces of metal
could approach 120 volts. Even a zinc/copper galvanic couple will result
in a measurable potential difference in seawater. No need for massive
currents and no need to think in terms of raising the potential of the
whole ocean. :-)

Draw out the circut and it will pop right out at you.

There are documented cases of swimmers and boaters suffering
electrocution from these problems. How probable? Different subject.
First let's establish how it could happen.

Chuck

chuck wrote in news:hAskf.8744$N45.1460
@newsread1.news.atl.earthlink.net:

Next, you grab your engine with one hand and open the door of your
fridge with the other as you reach for a cold one and you receive an
unhealthy dose of 60 Hz.



Wow...this scenario is pretty absurd, as I suspected, but I'll respond to
these unlikely events, anyways.

Point...there is NO PATH from your neighbor's boat prop to your boat prop
as the water between the boats IS EARTH GROUND....seawater to earth, a
great ground, even if it's a freshwater lake. The path from the
neighbor's absurd boat, taking the least resistance, is from the boat
into the conductive water to EARTH GROUND, back to the AC source. There
is absolutely no path to you and your absurd fridge. Don't believe me,
take ahold of the hot wire on the dock in one hand and simply touch your
finger to the water with the other. After picking up from the deck,
unplug the boat and try it again to see if there's more current...There's
not. You talk as if your neighbor's prop is only connected to your prop,
which just isn't so....

AS to the breaker trip. If you connect AC hot to the engine block in his
boat in seawater, I'd bet 50A would be just EASY! Seawater is a GREAT
conductor. Fresh water is a fair conductor. Try it yourself. Simply
drop the open plug from your boat into the water with the dock breaker
turned on. There'll be a little buzzing underwater before the breaker
overheats....and it eats the guts right out of the plug....

chuck wrote in news:hAskf.8744$N45.1460
@newsread1.news.atl.earthlink.net:

What happens, Larry, is that your fridge cabinet is connected to the
green equipment grounding conductor and to an AC ground/neutral
junction
on land. Your engine is connected through the water to the hot AC wire
on the neighboring boat. The voltage between those two pieces of metal
could approach 120 volts. Even a zinc/copper galvanic couple will
result
in a measurable potential difference in seawater. No need for massive
currents and no need to think in terms of raising the potential of the
whole ocean. :-)


Negative. The green wire is connected to EARTH GROUND. The engine is
connected to EARTH GROUND, too! The seawater IS EARTH GROUND!....and a
nice one it is. Your idea of floating the ocean 120VAC above that
grounded fridge cabinet just isn't gonna happen....

Hook a big ground symbol to the prop...That's the circuit....

Here, a much safer test. Plug the boat into the dock but leave the other
end unplugged from the boat. (leave the breaker off to be safer as we're
fooling with ground, not AC. Measure the resistance from the engine
block in the boat to the ground in the dropcord to the dock ground.
Unless you have a rubber shaft coupler somewhere...you'll find the
resistance VERY low through the water....salt water.

Still think the engine isn't grounded through the underwater metals?
Turn on the breaker and touch the black hot wire to the engine block and
tell me how big an arc it draws for you. Be careful the melting black
wire doesn't burn you....ok?

chuck wrote in news:hAskf.8744$N45.1460
@newsread1.news.atl.earthlink.net:

There are documented cases of swimmers and boaters suffering
electrocution from these problems. How probable? Different subject.
First let's establish how it could happen.

Chuck




Swimmers are electrocuted from being in the current path from his prop to
the bottom of the water. They're actually inside the conductor.

Measure the AC voltage from your engine block to the ground wire to the
dock....It's zero....(sigh)

chuck wrote in news:haikf.8489$N45.4470
@newsread1.news.atl.earthlink.net:

You can also isolate your underwater metal (prop,
shaft, etc.) from both the AC and DC ground systems, which may be what
you meant to suggest.


No, I mean to completely separate the DC negative bus/engine block from the
AC line Shore Ground bus....

There is no reason whatsoever for them to be connected together. The
transformer in the battery charger isolates them. The case of the battery
charger should be connected to the AC shore ground ONLY if it's made of
metal, which it no longer is any more. The metal case, if it has one, of
the AC/DC fridge should be connected to shore ground but NOT the battery
negative bus, either....

Shhhh....don't tell anyone.....Lionheart's HOUSE batteries are NOT
connected in any way to the STARTING battery's negative ground bus UNLESS
you reach under the aft cabin bunk and throw the grounding switch to
ON....allowing you to connect the house batteries to the engine for
emergency starting or charging the house batteries off the starting
battery's alternator in another emergency. Our house battery alternator is
connected to the house battery negative bus....NOT engine ground because
it's mounted to the boat on a separate bracket and uses a rubber belt.
Zincs last YEARS, not months. Nothing on the house circuit connects to
underwater that needs a zinc. There are no leakage paths....with even
separate DC negative busses.

Works great....(c;

(big snip)
There's absolutely NO reason why the independent DC system should be
connected to the AC ground bus I know of. Ours isn't.

One guy we know had a bozo miswire his shore cord, and while lying
along side his engine, grabbed hold of an AC grounded appliance frame. A
hearse was needed to transport him to the next event in his life.
Many of you have seen this waiting to happen, and maybe turned a little
skin into smoke.
Electricity is not foolproof! Eat your zincs out!

Lynn....... see these scars?

On 2005-12-02, Marc wrote:

Having disconnected and labeled all the 12 V wiring, the 110 AC is
now visable. It appears that all the AC ground wires (green) are run
to a common buss. But , then, the AC Ground buss is connected with
a 6 ga. wire to the DC negative buss. This doesn't seem right to me.
Is it?

unless the positive bus is connected to your hull (engine block etc...),
I see nothing wrong with grounding the negative bus

--

Bye.
Jasen

OK Marc,
These are the facts: first,on your incoming shorepower ground,you
would take care of any "stray current" problems caused by the marina or
other boats by installing a galvanic isolator....sometimes called a
zinc saver...almost all in-water boats made today have them installed
OEM...Second, your AC ground absolutely SHOULD be connected to the DC
ground buss, at 1 location only, to prevent ground loops....Why? Some
of these other posters have forgotten that just because you are not
connected to shore power,does not mean there is no AC power
present....ie.gensets and inverters....A gfi will do absolutely
nothing if there is no true earth ground, and if away from the dock,
that ground is seawater,via the ship ground(shaft, bonding system,
thru-hulls etc. Without that AC ground connection, you can become part
of the ground circuit if a fault occurs. That said, you should have a
seperate buss for each of the following: a neg. DC buss, a ship's
GROUND buss, and an AC ground buss...Note that the DC neg buss is for
connecting dc equipment to battery negative, the ship's GROUND buss is
for bonding all equipment and machinery and the protective anodes
together. Why connect the two? because in the event of a bad neg. DC
connection, say to an engine block, it prevents The DC current from
seeking an alternate path to the starter etc through seawater and the
bonding system itself. Therefore there should be 1 bond between the neg
DC and the ship's ground buss, and 1 bond between the AC ground buss
and either 1)neg DC buss, or 2) (preferred) Ship's ground buss. This is
not debateable or optional....it is absolutely necessary for
safety...Period.
If you have problems with rapid zinc consumption, you need to do a
complete corrosion survey with the proper equipment to determine the
source of the problem. Disconnecting the bond is like turning up the
stereo to make an engine noise go away...Someone else remarked about
the NEC and metal enclosures and sparks...He is wrong! each breaker IS
ignition protected...they don't use metal enclosures due to weight and
corrosion issues...This is a BOAT not a BUILDING, he needs to
familiarize himself with ABYC and Lloyd's Standards, they are the
applicable codes, and in almost all cases more stringent than the
NEC.,but written for the marine environment, not sitting on a piece of
dirt... Your SSB antenna better not be grounded or you'll cook your
radio the first time you send modulation.
SSB signals bounce off ground(called a counterpoise) which is seawater
connected by an RF ground, your bonding and thru hull system, a steel
hull, a metal fuel tank, or a dynaplate. This reflects the ssb signal
skyward. Marc, do it once and do it right...remember that your boat is
your total life support system when you're at sea... you can't walk out
the front door when there's a problem....think about that before taking
shortcuts or cutting corners to save money.
And not to stir up things, but I can tell you with certainty.....Listen
to Chuck, and forget
anything that Larry posted....Chuck is right on target,and knows
boats.....Guys like Larry are
responsible for a large portion of my income...
I have no problem correcting mistakes at $85.00/hour.. I'm not spouting
steam at you, I have over 25 years in the marine industry primarily in
electrical and electronics and plenty of schools and certs. It's
cheaper to do it right! Good Luck!
markvictor

Nice Post Mark. Thanks

"markvictor" wrote in message
oups.com...
OK Marc,
These are the facts: first,on your incoming shorepower ground,you
would take care of any "stray current" problems caused by the marina or
other boats by installing a galvanic isolator....sometimes called a
zinc saver...almost all in-water boats made today have them installed
OEM...Second, your AC ground absolutely SHOULD be connected to the DC
ground buss, at 1 location only, to prevent ground loops....Why? Some
of these other posters have forgotten that just because you are not
connected to shore power,does not mean there is no AC power
present....ie.gensets and inverters....A gfi will do absolutely
nothing if there is no true earth ground, and if away from the dock,
that ground is seawater,via the ship ground(shaft, bonding system,
thru-hulls etc. Without that AC ground connection, you can become part
of the ground circuit if a fault occurs. That said, you should have a
seperate buss for each of the following: a neg. DC buss, a ship's
GROUND buss, and an AC ground buss...Note that the DC neg buss is for
connecting dc equipment to battery negative, the ship's GROUND buss is
for bonding all equipment and machinery and the protective anodes
together. Why connect the two? because in the event of a bad neg. DC
connection, say to an engine block, it prevents The DC current from
seeking an alternate path to the starter etc through seawater and the
bonding system itself. Therefore there should be 1 bond between the neg
DC and the ship's ground buss, and 1 bond between the AC ground buss
and either 1)neg DC buss, or 2) (preferred) Ship's ground buss. This is
not debateable or optional....it is absolutely necessary for
safety...Period.
If you have problems with rapid zinc consumption, you need to do a
complete corrosion survey with the proper equipment to determine the
source of the problem. Disconnecting the bond is like turning up the
stereo to make an engine noise go away...Someone else remarked about
the NEC and metal enclosures and sparks...He is wrong! each breaker IS
ignition protected...they don't use metal enclosures due to weight and
corrosion issues...This is a BOAT not a BUILDING, he needs to
familiarize himself with ABYC and Lloyd's Standards, they are the
applicable codes, and in almost all cases more stringent than the
NEC.,but written for the marine environment, not sitting on a piece of
dirt... Your SSB antenna better not be grounded or you'll cook your
radio the first time you send modulation.
SSB signals bounce off ground(called a counterpoise) which is seawater
connected by an RF ground, your bonding and thru hull system, a steel
hull, a metal fuel tank, or a dynaplate. This reflects the ssb signal
skyward. Marc, do it once and do it right...remember that your boat is
your total life support system when you're at sea... you can't walk out
the front door when there's a problem....think about that before taking
shortcuts or cutting corners to save money.
And not to stir up things, but I can tell you with certainty.....Listen
to Chuck, and forget
anything that Larry posted....Chuck is right on target,and knows
boats.....Guys like Larry are
responsible for a large portion of my income...
I have no problem correcting mistakes at $85.00/hour.. I'm not spouting
steam at you, I have over 25 years in the marine industry primarily in
electrical and electronics and plenty of schools and certs. It's
cheaper to do it right! Good Luck!
markvictor

Thanks John,
I hate to see people get screwed up by bad info..
One of the most common things I hear on service calls is "my buddy
hooked it up for me" or "my buddy said all I had to do was..."
I hate to tell them, but he's not their buddy, he's MY buddy!
Sad but true.....
markvictor