The danger of using a simple extension cord shows up when the boater in
the next slip manages to connect the hot 120 volt wire to the water.

There are a number of classic ways in which this has been done, such as
with automotive battery chargers, home-wired extension cords, etc.

No, his breaker won't trip because the current through the water will
not rise to the 15 amp level. That unhealthy situation could exist
undetected for months. So you now place one hand on the mast and grab
the coffee pot with the other and electrocution is possible.

Of course, in a glass boat with no metal under water, you'd probably be
safe (not the case with most sailboats though).

The idea is to make sure that the boat's AC ground (connected to the
water) is at the same potential as the green grounding wire on the shore
power system. You do that by connecting the two.

Chuck

Lew Hodgett wrote:
bob wrote:

I want to add a simple shore power hook-up.

snip

Absolutely the simplest, safest, most reliable, lowest cost system is a
simple extension cord.

Plug one end into shore power, bring the other end on board and plug the
coffee pot,etc into it.

You will need a 30A/15A adapter to accept the coffee pot, etc which is a
simple item to make.

Lew

chuck wrote in news:nfnRf.3818$k75.3159
@newsread3.news.atl.earthlink.net:

So you now place one hand on the mast and grab
the coffee pot with the other and electrocution is possible.


Couldn't we just put the coffee pot in the galley, instead of on top of the
cabin near the mast?....(c;

By the way, the coffee pot is NOT hooked to either side of the line, so
you'll have to touch the mast and the internal wiring terminals inside the
boiler at the same time to get shocked. Anyone stupid enough to do that
deserves to die. I've never been shocked by touching the plastic case on a
coffee pot, however...

Sure thing, Larry.

I agree: a plastic case on a double-insulated pot ought to be pretty
safe. What I really had in mind though was an appliance that had the
equipment grounding conductor connected to the case. Some electric
drills and other power tools possibly found on boats still use metal
cases and three-prong plugs. As for the mast, for many of us, the mast
is IN the galley, along with the engine, and most everything else. )

Chuck

Larry wrote:
chuck wrote in news:nfnRf.3818$k75.3159
@newsread3.news.atl.earthlink.net:


So you now place one hand on the mast and grab
the coffee pot with the other and electrocution is possible.



Couldn't we just put the coffee pot in the galley, instead of on top of the
cabin near the mast?....(c;

By the way, the coffee pot is NOT hooked to either side of the line, so
you'll have to touch the mast and the internal wiring terminals inside the
boiler at the same time to get shocked. Anyone stupid enough to do that
deserves to die. I've never been shocked by touching the plastic case on a
coffee pot, however...

chuck wrote in news:1vpRf.11533$S25.11273
@newsread1.news.atl.earthlink.net:

I agree: a plastic case on a double-insulated pot ought to be pretty
safe. What I really had in mind though was an appliance that had the
equipment grounding conductor connected to the case. Some electric
drills and other power tools possibly found on boats still use metal
cases and three-prong plugs. As for the mast, for many of us, the mast
is IN the galley, along with the engine, and most everything else. )



The drop-in-cord is still a 3-prong grounded AC feed. I don't understand
about connecting shore ground to the engine block and underwater metal
parts or the mast. The 3-prong grounded-through-the-drop-cord case of
the 120V fridge-from-Walmart is at ground potential. The only voltage
that's going to be on its case to the engine block in your boat is the
electrolysis DC potential between the metal conduit under the dock all
rusted out and leaking and your zincs, which will be fizzing away
protecting the rotting conduit if you connect their ground to your engine
block.

Is your mast grounded to the engine? Most are just floating to make sure
and lightning strike holes the hull to sink the whole thing so they can
sell you a new boat. Measure resistance between the mast and the
negative terminal on any 12V light near it. I bet it's an open circuit.
Grounding straps running through fiberglass boats costs them money to
install. You just know they're not going to do it, right?

I don't understand how grounding the AC line to the boat's DC circuit is
going to be "safer". If you get between AC "hot", the black wire, and
the boat's ground to the seawater, you get a shock limited by the
resistance of the connection to the seawater, which isn't much. If you
ground the AC line to all the boat's equipment, you get a shock with only
you as the resistance limiting the current that's going to kill you, just
like at home! How is that "safer"?? I'll be glad to come to your boat
and hold onto AC ground or neutral in one hand and the engine block in
the other, any time....grounded or not. I won't get shocked.

If we were interested in AC line safety, every marina would simply be
FORCED, the only way to make it happen, to comply with an NEC requirement
to install ground fault interrupters to all dock breaker panels out there
in the little post out front. Noone would ever get shocked, again,
unless they got right across the AC line to neutral. Of course, noone
would have any AC power in the boat, either, because the leakage of all
those old rusty fridges, water heaters and battery chargers would trip
the hell out of all the dock GFIs, plunging the boats in the dark,
too!...(c; Don't worry, noone at the marina or NEC cares.

Someone sent me a picture of total stupidity. This guy is standing in
his bare feet on a metal stepladder in the middle of a swimming pool in
his bathing suit. He's drilling a hole in the ceiling for something with
a metal-cased old electric drill. If you follow the cord back you see
it's plugged into a little brown 2-wire extension cord. You can see the
ground pin on the drill's electric cord sticking out in mid air. Totally
Stupid is right!...(c;

Well Larry, I know from previous posts that this issue troubles you.

What the analysis hinges on is what happens when the boat next to you
connects the 120 volt hot wire to his DC ground system (prop, etc. below
the water). Did you skip that part of the post? Did you tune it out
because you know in your heart the the guy on the boat next to yours
would never do such a thing?

Your view (rhetoric aside) seems to be that in the above example, the
water will provide a return path to the shore power connections and
what? trip a breaker? or just create a whopping electric field between
the prop and whatever is the lowest resistance path back to the shore
power ground connection? Or maybe you have some other analysis of what
happens. You really can't ignore that part of the analysis and then
conclude there is no safety hazard.

The scenario I've tried to describe considers that the shortest path
from the prop of the boat in the next slip to the shore power grounding
point MIGHT be through YOUR prop to your DC ground system (engine or
whatever it is connected to on the boat).

Even if that path is not the one with the LOWEST resistance, it may
still provide sufficiently low resistance to cause electrocution if
someone touches both the engine and the green shore power grounding
conductor. Does that bit of Ohm's law trouble you after all these years?

Of course it is true that if there are no other boats in sight, and no
other opportunities for messed-up wiring near your boat, you will have
no problems with shock hazards. Think about what you're saying for a
moment, Larry. You agree that galvanic currents can pass through the
water from boat to boat even though these are less than a couple of
volts, but you are positive that 120 VAC currents would never do so
between the same two pieces of metal. How do you explain that? Ohm's law
again?

To keep this reasonable short, I'm lumping salt water and fresh water
analysis together, even though the problem is more serious with fresh water.

Chuck




Larry wrote:
chuck wrote in news:1vpRf.11533$S25.11273
@newsread1.news.atl.earthlink.net:


I agree: a plastic case on a double-insulated pot ought to be pretty
safe. What I really had in mind though was an appliance that had the
equipment grounding conductor connected to the case. Some electric
drills and other power tools possibly found on boats still use metal
cases and three-prong plugs. As for the mast, for many of us, the mast
is IN the galley, along with the engine, and most everything else. )




The drop-in-cord is still a 3-prong grounded AC feed. I don't understand
about connecting shore ground to the engine block and underwater metal
parts or the mast. The 3-prong grounded-through-the-drop-cord case of
the 120V fridge-from-Walmart is at ground potential. The only voltage
that's going to be on its case to the engine block in your boat is the
electrolysis DC potential between the metal conduit under the dock all
rusted out and leaking and your zincs, which will be fizzing away
protecting the rotting conduit if you connect their ground to your engine
block.

Is your mast grounded to the engine? Most are just floating to make sure
and lightning strike holes the hull to sink the whole thing so they can
sell you a new boat. Measure resistance between the mast and the
negative terminal on any 12V light near it. I bet it's an open circuit.
Grounding straps running through fiberglass boats costs them money to
install. You just know they're not going to do it, right?

I don't understand how grounding the AC line to the boat's DC circuit is
going to be "safer". If you get between AC "hot", the black wire, and
the boat's ground to the seawater, you get a shock limited by the
resistance of the connection to the seawater, which isn't much. If you
ground the AC line to all the boat's equipment, you get a shock with only
you as the resistance limiting the current that's going to kill you, just
like at home! How is that "safer"?? I'll be glad to come to your boat
and hold onto AC ground or neutral in one hand and the engine block in
the other, any time....grounded or not. I won't get shocked.

If we were interested in AC line safety, every marina would simply be
FORCED, the only way to make it happen, to comply with an NEC requirement
to install ground fault interrupters to all dock breaker panels out there
in the little post out front. Noone would ever get shocked, again,
unless they got right across the AC line to neutral. Of course, noone
would have any AC power in the boat, either, because the leakage of all
those old rusty fridges, water heaters and battery chargers would trip
the hell out of all the dock GFIs, plunging the boats in the dark,
too!...(c; Don't worry, noone at the marina or NEC cares.

Someone sent me a picture of total stupidity. This guy is standing in
his bare feet on a metal stepladder in the middle of a swimming pool in
his bathing suit. He's drilling a hole in the ceiling for something with
a metal-cased old electric drill. If you follow the cord back you see
it's plugged into a little brown 2-wire extension cord. You can see the
ground pin on the drill's electric cord sticking out in mid air. Totally
Stupid is right!...(c;