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

So you're saying not to ground the AC ground at the boat, but to rely on the
shore ground? Everything I've read says you must ground it at the boat as
a safety precaution against faulty grounding at the dock. Did I
misunderstand something?

I can't (conveniently) isolate my house DC from ground since I have a
non-isolated ground alternator.

Don't SSB antennas need to be grounded? Do the radios isolate the antenna
ground from DC ground?


"Larry" wrote in message
...
"johnhh" wrote in
:

So are you complaining that the AC ground and DC negative are both
connected to the boats ground
"Boats ground"? What's that? The boat is made of PLASTIC, an insulator.
It has no "ground". It has a negative battery bus. It has an AC supply
ground connected to the shore power ground system. What's the "boats
ground"?

I hear this a lot. It doesn't exist. The battery negative bus has no
relationship, whatsoever, to the AC shore power ground as the two systems
are totally isolated from each other unless there is something wrong with
your battery charger, dual-voltage fridge or other AC/DC components.

Touching the AC shore grounded appliance, already hooked to AC shore
ground, with one hand and touching the engine block connected to the sea
and DC ground bus results in no hazard...unless the AC shore ground is
defective PLUS the appliance or device is defective. Touching an AC
grounded device with one hand and a defective 2-wire toaster with the hot
lead of the AC line hooked to its metal case has the SAME SHOCK as
touching the DC ground bus hooked to the engine block....unless, of
course, the boat has a proper GFI that should, but is not, required
aboard the boat....just like proper NEC-approved breaker panels are not.
(A bunch of little plastic breakers on a plastic panel screwed into a
flammable wooden box made of some exotic, expensive wood is NOT up to the
National Electric Code of the USA or any country with any brains. AC and
DC panels in boats are made that way to SAVE MANUFACTURERS MONEY. They
are NOT "safe", from fire (flammable) or explosion (not sealed against
fumes) at all!

Ok, back to the buses connected together for some stupid reason.....

If the DC bus hooked to the zincs by virtue of the DC bus being connected
to the engine block....is connected directly to the AC bus ground back to
shore power ground through the boat's impressive yellow shore cable, this
connects the boat's zincs STRAIGHT TO THE BOTTOM OF THE HARBOR...not to
mention every other boat wired this stupid way. YOUR zincs are hooked to
HIS underwater metal parts through the common-connected AC shore power
ground wires.

So? What happens now?........(you ask).....

Ever notice the metal conduit hanging loose under every dock on every
marina in the country? See how it hangs into the water? If I hook MY
zincs to that metal conduit (by the AC shore power ground wire from the
boat with the DC negative bus hooked to AC shore power ground), MY zinc
will fizz away protecting the rotting plating on that sagging conduit,
every little ground wire touching anything conductive hooked to the
water, and even the ground rod back at the feed point from the power
company! Isn't that nice of me?

Is it any wonder some people are going through those amazingly-expensive
zincs at an alarming rate in your marina? Zincs protect what they are
CONNECTED to. They are a virual shorted battery, the zinc one plate, any
metal part making connections with the water the other plate and seawater
as the electrolyte. In order for the battery to DISCHARGE, eating the
zinc, it has to have a DIRECT DC PATH from the zinc to that plate.
Unhook the path, you've opened the shorted battery circuit. The only
battery plate the UNHOOKED boat makes a battery with is the metal part
the zinc is mounted on and is protecting, not every neighboring boat
connected to the AC power shore ground.

Every AC device in the boat, with, of course, the exception of insulated,
UL-approved, appliances-electronics-doubleinsulated drills-etc....should
be hooked for safety to the SHORE GROUND, to prevent the AC line from
appearing on the metal cabinet parts of it. Of course, it would be nice
if the damned AC panel, ITSELF, on pleasure boats were so connected.
They're not. Look into the wooden box. Metal breaker panel hooked to
green wire? Not most.

If you disconnect the DC negative bus from the AC Shore Ground green
wire, you measure the DC potential caused by the zincs...the
electroplating voltage trying to destroy the zincs. It CAN'T have any AC
voltage between the Shore Ground hooked to a ground rod somewhere and the
DC ground bus hooked to the engine block....doesn't wash.

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)

"johnhh" wrote in
:

So you're saying not to ground the AC ground at the boat, but to rely
on the shore ground? Everything I've read says you must ground it at
the boat as a safety precaution against faulty grounding at the dock.
Did I misunderstand something?



The boat is made of PLASTIC. You cannot ground the fiberglass. If you
have a steel hull, I still wouldn't connect the green wire to it. It is
already "grounded" through the seawater. You'd just add to your galvanic
action problem. You may not be able to isolate it as the grounded
equipment is hooked to the hull in lots of places, anyways. Fiberglass
boats are being discussed.
All AC grounds are to be connected to shore power "ground". This insures
you get knocked on your ass if you touch AC hot and the grounded fridge
case. But, that's the way they want it. Buy a plastic cased fridge,
problem solved. The battery charger should have its DC circuit isolated
from its AC circuit. If it's not, I wouldn't buy it. The + and -
charging terminals should be totally isolated from the power-line-
grounded case.

If you tie the "faulty ground" at the dock, let's say it's open from
corrosion or the wire is busted, connected or not to DC ground in the
boat...it's still open. If the plug is wired wrong, the AC box is still
grounded to ground. You'll get knocked on your ass plugging your
grounded plug in if it doesn't explode in your hand before the breaker
trips. Grounding the hot AC line through the faulty hot-connected-to-
green-wire-to-the-boat absurd scenario in the DC to AC interconnected
ground scenario only results in a big flash as the AC current has a
direct path to ground through the engine block/propshaft, tripping the
breaker I hope unless some other absurd scenario has it bypassed....

I'll be absurd, too. Every boater should have a ground detector built
right into the AC breaker panel!

On Sat, 03 Dec 2005 18:54:28 -0500, Larry wrote:

"johnhh" wrote in
:

So are you complaining that the AC ground and DC negative are both
connected to the boats ground
"Boats ground"? What's that? The boat is made of PLASTIC, an insulator.
It has no "ground". It has a negative battery bus. It has an AC supply
ground connected to the shore power ground system. What's the "boats
ground"?
Not everbody has a "Tupperware" boat Larry. Some of us have steel
boats. I sincerely hope that your philosophy changes for these.

The best problem that I found on a boat was the following.

Steel boat in at a dock connected to 240v shoreline.
Boat was pressure washed and sparks were seen when the lance touched
the hull.
I was asked to check it out.
Finally found that the hull was sitting at 24v dc above shore ground.
Went searching and found that the metal end cover on the charger was
touching an uninsulated crimp lug. The DC -ve was not connected to the
hull.
If the system had been installed correctly this would not have
happened.
I am glad that my Steel hull was not mored nearby!!!

Richard

Nb "Pound Eater" Parkend G+S

Larry, I think your conclusions are based on some incorrect assumptions
regarding the path resistances through earth and water.

The beginning point of disagreement may be your assertion that seawater
is a great conductor. Compared to copper, seawater is a terrible
conductor: orders of magnitude worse, in fact. I admit it is not easy to
do actual calculations on the resistance of a particular seawater path
using specific electrodes, since path resistance will depend on surface
areas of the electrodes and the distance between them, in addition to
the resistivity or conductivity of the seawater. But the concept should
be clear.

At 120 volts, a 50 ampere circuit would require a path resistance of 2.4
ohms. There is no way you can find a six foot path from your prop to the
earth below back to the ground/neutral AC connection point with a
resistance of 2.4 ohms. Even if the water path resistance were zero
ohms, (which would be low by some orders of magnitude) the earth itself
will constitute more than 2.4 ohms resistance. I would not advise you to
do this with 120 volts, but with a 6 volt transformer, connect one side
to your prop and the other side to your green AC grounding conductor and
measure the current and calculate the resistance of the path. The path
will be from the transformer to your prop through the water to the earth
through the earth to the ground/neutral connection point and then back
to your transformer through the green grounding conductor. Tell us what
you find.

So even if the path resistance through the water from your prop to the
prop in the next slip is an order of magnitude greater (quite unlikely)
than the path resistance from his prop back through the earth to the
ground/neutral connection point, there will still be a voltage between
your prop and green grounding wire on your boat (which has negligible
resistance back to the ground/neutral connection point). It is quite
possible that the path through your prop and green grounding wire will
have lower resistance than the path from the neighbor's prop through the
water and the earth.

Bottom line: what you have is an AC voltage connected to two parallel
resistances. But the key point is that these resistances are
sufficiently high that when a human body's resistance is added in
parallel with them, enough current will flow through the body to cause
electrocution.

FWIW, I think you are attempting to apply electrostatics principles to
this situation. It is quite true that if you have an object with a net
positive or negative charge and touch it to earth (or water) that net
charge will dissipate through the earth (or water). That simply doesn't
happen here. If you apply a voltage to two electrodes stuck in the earth
(or the water) you will find that depending on the parameters mentioned
above, a finite resistance is encountered. Place the human body's
resistance in parallel with that resistance and some current will flow
through the body. Not telling you a thing here, Larry, just that the
issue is really the magnitudes of the path resistances involved. Even at
RF, seawater does not offer anything close to a zero ground loss
resistance. Depending on a lot of things, some radial systems on earth
are actually far better largely because of water's relatively lower
conductivity. The confusion over the properties of seawater at RF arises
from the fact that refelctions from seawater are far superior to
reflections from any known earth types and this superiority is sometimes
incorrectly transferred to seawater's performance as a ground plane. But
that's for a different time.

Regards,

Chuck

Larry wrote:
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....

Jeez Larry, I didn't say anything about grounding anything to a plastic
hull. I also did not say that the AC ground should not be grounded at the
shore side. I said that everything I have read says it should also be
grounded at the boat end. Just like that grounding rod outside my wood
house.


"Larry" wrote in message
...
"johnhh" wrote in
:

So you're saying not to ground the AC ground at the boat, but to rely
on the shore ground? Everything I've read says you must ground it at
the boat as a safety precaution against faulty grounding at the dock.
Did I misunderstand something?



The boat is made of PLASTIC. You cannot ground the fiberglass. If you
have a steel hull, I still wouldn't connect the green wire to it. It is
already "grounded" through the seawater. You'd just add to your galvanic
action problem. You may not be able to isolate it as the grounded
equipment is hooked to the hull in lots of places, anyways. Fiberglass
boats are being discussed.
All AC grounds are to be connected to shore power "ground". This insures
you get knocked on your ass if you touch AC hot and the grounded fridge
case. But, that's the way they want it. Buy a plastic cased fridge,
problem solved. The battery charger should have its DC circuit isolated
from its AC circuit. If it's not, I wouldn't buy it. The + and -
charging terminals should be totally isolated from the power-line-
grounded case.

If you tie the "faulty ground" at the dock, let's say it's open from
corrosion or the wire is busted, connected or not to DC ground in the
boat...it's still open. If the plug is wired wrong, the AC box is still
grounded to ground. You'll get knocked on your ass plugging your
grounded plug in if it doesn't explode in your hand before the breaker
trips. Grounding the hot AC line through the faulty hot-connected-to-
green-wire-to-the-boat absurd scenario in the DC to AC interconnected
ground scenario only results in a big flash as the AC current has a
direct path to ground through the engine block/propshaft, tripping the
breaker I hope unless some other absurd scenario has it bypassed....

I'll be absurd, too. Every boater should have a ground detector built
right into the AC breaker panel!

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