I don't want to rain on your parade here, but bad shore power is very common
and the guy next door is not causing it. The problem is that there is at
least one consumer on your distribution transformer that has a current leak
to safety ground. In an ideal world that leak should flow to earth through
the neutral to safety earth connection at the distribution transformer, but
as you are in a marina and your hull earth is a lot better than the corroded
earth rod at the transformer, the energy leak is flowing through your hull.
That is the reason for using an isolation transformer. In any case never
connect the shore point safety earth to your hull. Do exactly like your
neighbor did, connect only phase and neutral. On your boat make certain all
safety earth connections connect to your hull only. It is just as safe for
YOU, but the dock has a serious SAFETY issue. Any person touching a dock
earthed point and the water could be shocked. This is NOT code, but the
shock is significantly less on your wallet.
Steve

wrote in message
oups.com...
There is another thtread about someone with a bad shore power
connection and what to do with it. I agree, the guy has no right to
endanger others. I consider myself to be a fairly knowledgeable person
but had never had my boat in a marina and never had shore power so I
was not familiar with the dangers. When cruising, we stayed in a
marina for the first time. I decided to swim to check my prop for
fouling as I always did.
The water felt really strange, sorta tingly all over. My shaft zinc
that had just been installed a month ago was nearly gone. I was in
mask and snorkel looking at it trying to figure it out when it suddenly
occurred to me, ELECTRICITY! I swam away from the boats without
touching anything and got out of the water at the shore. Sure enough,
the guy next to me had a bizarro shore power cord with two prongs, just
regular zip cord.

Steve Lusardi wrote:
I don't want to rain on your parade here, but bad shore power is very common
and the guy next door is not causing it. The problem is that there is at
least one consumer on your distribution transformer that has a current leak
to safety ground. In an ideal world that leak should flow to earth through
the neutral to safety earth connection at the distribution transformer, but
as you are in a marina and your hull earth is a lot better than the corroded
earth rod at the transformer, the energy leak is flowing through your hull.
That is the reason for using an isolation transformer. In any case never
connect the shore point safety earth to your hull. Do exactly like your
neighbor did, connect only phase and neutral. On your boat make certain all
safety earth connections connect to your hull only. It is just as safe for
YOU, but the dock has a serious SAFETY issue. Any person touching a dock
earthed point and the water could be shocked. This is NOT code, but the
shock is significantly less on your wallet.
Steve

wrote in message
oups.com...
There is another thtread about someone with a bad shore power
connection and what to do with it. I agree, the guy has no right to
endanger others. I consider myself to be a fairly knowledgeable person
but had never had my boat in a marina and never had shore power so I
was not familiar with the dangers. When cruising, we stayed in a
marina for the first time. I decided to swim to check my prop for
fouling as I always did.
The water felt really strange, sorta tingly all over. My shaft zinc
that had just been installed a month ago was nearly gone. I was in
mask and snorkel looking at it trying to figure it out when it suddenly
occurred to me, ELECTRICITY! I swam away from the boats without
touching anything and got out of the water at the shore. Sure enough,
the guy next to me had a bizarro shore power cord with two prongs, just
regular zip cord.




Hello Steve,

I would caution strongly against using the
water-earth path in lieu of the green equipment
grounding conductor. Ever.

The purpose of that conductor is to provide a low
impedance path for the purpose of clearing a
ground fault.

In proper wiring, the impedance is no more than a
few ohms and the fault is cleared at a breaker.
Fault current does NOT flow through the earth.

By contrast, the water-earth path may have a
resistance of 25 ohms or more for salt water, and
tens of thousands of ohms or more for fresh water.
This path will NOT clear a ground fault. It will
not trip a 20 A breaker. Witness the 120 volt
power cords dropped off a dock without tripping a
breaker!

If one has a problem with wiring impedances in the
marina, deal with it by getting the wiring
inspected. Ask the marina operator when it was
last checked. Yell. Scream. Buy your own tester
and tell the marina what you measured. Tell the
other boaters. Take names and publish on the
Internet. But don't throw out the safety net
because even with corroded connections, the wiring
may still allow a ground fault to be cleared.

If there is a problem with a nearby source (boat
or otherwise) then an isolation transformer would
be a good idea.

But even with an isolation transformer, always use
approved wiring practices. There is probably no
more thoroughly reviewed standard than the NEC.
The ABYC standards for AC wiring are similarly solid.

And install GFCIs for the smaller ground fault
currents that won't trip a regular breaker but can
electrocute.

Good luck.

Chuck



















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Chuck,
I don't think you understand the problem. If there is a ground fault
detecting breaker some where in the distribution net, it clearly should
function whether or not we elect to use the green equipment line or not at
the service point. I agree that the green wire should provide a low
impedance path to earth. In fact , as I stated, that connection must be made
at the distribution transformer. The problem is that the low impedence path
provided at the transformer will NEVER be as low an impedance path to earth
as your hull is. Therefore energy leakage to earth anywhere within the net,
we are now talking about the whole marina, will route itself to your hull
simply because it is a better ground than the one provided at the
transformer.

Your statement that fault current does not flow through the green wire
cuircuit is flat incorrect. That is its sole purpose. The inverse is also
true, if there is no fault, no current will flow there. If we take the case
of the in-line AC line filter, you know, the capacitor type with the metal
case that bolts to equipment frames? Or granny's 25 year old vacuum cleaner
with worn out brushes and carbon dust all around the commutator? All that is
leakage current. Now, I concede that the earth point at the transformer is
also the neutral tranformer leg tie point and the leakage also returns to
the transformer at that point, but your hull has also created a huge ground
loop in the net and by default routes all earth reference current through
your hull.

Please also remember that your boat, if wired correctly, is a complete power
system AC and DC all properly tied together at your hull ground plate and
when hooking directly to shore power without an isolation transformer, you
are paralleling the shore based grid and the ground connection you make is
effectively an equalization bus and every code book I have ever read clearly
states that an equalization bus should never be longer than one meter. So
the correct advice is, if you don't want to waste your metal bits below the
waterline due to electrolosis and galvanic protection is your goal, never
direct wire to shore power. Instead, you should couple your energy
magnetically through the use of an isolation transformer and leave other's
faults to themselves.
Steve

Hello Steve,

I would caution strongly against using the water-earth path in lieu of the
green equipment grounding conductor. Ever.

The purpose of that conductor is to provide a low impedance path for the
purpose of clearing a ground fault.

In proper wiring, the impedance is no more than a few ohms and the fault
is cleared at a breaker. Fault current does NOT flow through the earth.

By contrast, the water-earth path may have a resistance of 25 ohms or more
for salt water, and tens of thousands of ohms or more for fresh water.
This path will NOT clear a ground fault. It will not trip a 20 A breaker.
Witness the 120 volt power cords dropped off a dock without tripping a
breaker!

If one has a problem with wiring impedances in the marina, deal with it by
getting the wiring inspected. Ask the marina operator when it was last
checked. Yell. Scream. Buy your own tester and tell the marina what you
measured. Tell the other boaters. Take names and publish on the Internet.
But don't throw out the safety net because even with corroded connections,
the wiring may still allow a ground fault to be cleared.

If there is a problem with a nearby source (boat or otherwise) then an
isolation transformer would be a good idea.

But even with an isolation transformer, always use approved wiring
practices. There is probably no more thoroughly reviewed standard than the
NEC. The ABYC standards for AC wiring are similarly solid.

And install GFCIs for the smaller ground fault currents that won't trip a
regular breaker but can electrocute.

Good luck.

Chuck



















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Steve Lusardi wrote:

Chuck,
I don't think you understand the problem. If there is a ground fault
detecting breaker some where in the distribution net, it clearly should
function whether or not we elect to use the green equipment line or not at
the service point.

OK. You are referring to a GFCI or ground fault
breaker. You are correct, provided that only 125
volt circuits are involved. Such a device in a
250/125 volt circuit will not detect ground
faults. Many boats utilize 250/125 volt systems.
Not all marinas and not all boats utilize GFCI
equipment. In any case, your original post, to
which I responded, made no mention of GFCI protection.

I agree that the green wire should provide a low
impedance path to earth. In fact , as I stated, that connection must be made
at the distribution transformer. The problem is that the low impedence path
provided at the transformer will NEVER be as low an impedance path to earth
as your hull is. Therefore energy leakage to earth anywhere within the net,
we are now talking about the whole marina, will route itself to your hull
simply because it is a better ground than the one provided at the
transformer.

What you are saying here suggests you are thinking
about charge distribution in the earth, as is
important in lightning protection but I don't
think it applies to this discussion.

The green wire is connected to the earth (and
water) to maintain people in contact with the
earth and equipment cases at the same potential.
This is somewhat different from the ground fault
clearing function of the green wire. It is an
important function because even small leakage
currents flowing from a hot wire-to-equipment case
connection (not a direct short) through a person
to earth (or water) can be dangerous. So even
though the current is too small to clear the
fault, it may nonetheless be dangerous and we can
minimize its danger by keeping the equipment case
and the person at the same potential. Hence: the
green wire is connected to ground. Whether you are
on water or earth, there is no guarantee you will
ever be at exactly the same potential as someone
else, even a few feet away.

GFCIs for 125 volts can provide even better
protection when leakage currents are detected.


Your statement that fault current does not flow through the green wire
cuircuit is flat incorrect. That is its sole purpose.

Of course. My exact words:

The purpose of that conductor is to provide a
low impedance path for the
purpose of clearing a ground fault.

My point was that the path through the water and
earth has too high a resistance to clear a ground
fault. A connection from an appliance case to
ground is NOT a substitute for a low impedance
equipment grounding wire back to the distribution
panel.

The inverse is also
true, if there is no fault, no current will flow there. If we take the case
of the in-line AC line filter, you know, the capacitor type with the metal
case that bolts to equipment frames? Or granny's 25 year old vacuum cleaner
with worn out brushes and carbon dust all around the commutator? All that is
leakage current. Now, I concede that the earth point at the transformer is
also the neutral tranformer leg tie point and the leakage also returns to
the transformer at that point, but your hull has also created a huge ground
loop in the net and by default routes all earth reference current through
your hull.

Please also remember that your boat, if wired correctly, is a complete power
system AC and DC all properly tied together at your hull ground plate and
when hooking directly to shore power without an isolation transformer, you
are paralleling the shore based grid and the ground connection you make is
effectively an equalization bus and every code book I have ever read clearly
states that an equalization bus should never be longer than one meter.

Perhaps I'm misunderstanding, Steve, but every one
of the millions of residences in the US subject to
the NEC parallels the shore based grid and ground
connection. While not a perfect system design, I
don't believe it bears on our discussion.

So
the correct advice is, if you don't want to waste your metal bits below the
waterline due to electrolosis and galvanic protection is your goal, never
direct wire to shore power. Instead, you should couple your energy
magnetically through the use of an isolation transformer and leave other's
faults to themselves.

Again, I fully agree that a properly installed
isolation transformer is one of several ways that
galvanic currents through the shore power
grounding conductor can be mitigated. I continue
to maintain that the grounding conductor should be
utilized from the dock pedestal to the isolation
transformer connection at the primary. At the
secondary, you should create and use your own
grounding conductor by connecting to the
secondary's neutral for that purpose.


Chuck

Steve
Hello Steve,

I would caution strongly against using the water-earth path in lieu of the
green equipment grounding conductor. Ever.

The purpose of that conductor is to provide a low impedance path for the
purpose of clearing a ground fault.

In proper wiring, the impedance is no more than a few ohms and the fault
is cleared at a breaker. Fault current does NOT flow through the earth.

By contrast, the water-earth path may have a resistance of 25 ohms or more
for salt water, and tens of thousands of ohms or more for fresh water.
This path will NOT clear a ground fault. It will not trip a 20 A breaker.
Witness the 120 volt power cords dropped off a dock without tripping a
breaker!

If one has a problem with wiring impedances in the marina, deal with it by
getting the wiring inspected. Ask the marina operator when it was last
checked. Yell. Scream. Buy your own tester and tell the marina what you
measured. Tell the other boaters. Take names and publish on the Internet.
But don't throw out the safety net because even with corroded connections,
the wiring may still allow a ground fault to be cleared.

If there is a problem with a nearby source (boat or otherwise) then an
isolation transformer would be a good idea.

But even with an isolation transformer, always use approved wiring
practices. There is probably no more thoroughly reviewed standard than the
NEC. The ABYC standards for AC wiring are similarly solid.

And install GFCIs for the smaller ground fault currents that won't trip a
regular breaker but can electrocute.

Good luck.

Chuck



















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Chuck,
You are not misunderstanding. In fact you have an excellent understanding of
the problem. Our discussion has led us to your statement below and while you
are correct that the same code is used for millions of residences, they
don't float and are not subject to galvanic damage and because of that, it
does bear on our discussion. My point is that code is not appropriate for
marina use. So it comes down to personal choice. I use a custom made
isolation transformer, they are cheap insurance.
Steve

Perhaps I'm misunderstanding, Steve, but every one of the millions of
residences in the US subject to the NEC parallels the shore based grid and
ground connection. While not a perfect system design, I don't believe it
bears on our discussion.

So
the correct advice is, if you don't want to waste your metal bits below
the waterline due to electrolosis and galvanic protection is your goal,
never direct wire to shore power. Instead, you should couple your energy
magnetically through the use of an isolation transformer and leave
other's faults to themselves.

Again, I fully agree that a properly installed isolation transformer is
one of several ways that galvanic currents through the shore power
grounding conductor can be mitigated. I continue to maintain that the
grounding conductor should be utilized from the dock pedestal to the
isolation transformer connection at the primary. At the secondary, you
should create and use your own grounding conductor by connecting to the
secondary's neutral for that purpose.


Chuck

Steve
Hello Steve,

I would caution strongly against using the water-earth path in lieu of
the green equipment grounding conductor. Ever.

The purpose of that conductor is to provide a low impedance path for the
purpose of clearing a ground fault.

In proper wiring, the impedance is no more than a few ohms and the fault
is cleared at a breaker. Fault current does NOT flow through the earth.

By contrast, the water-earth path may have a resistance of 25 ohms or
more for salt water, and tens of thousands of ohms or more for fresh
water. This path will NOT clear a ground fault. It will not trip a 20 A
breaker. Witness the 120 volt power cords dropped off a dock without
tripping a breaker!

If one has a problem with wiring impedances in the marina, deal with it
by getting the wiring inspected. Ask the marina operator when it was
last checked. Yell. Scream. Buy your own tester and tell the marina what
you measured. Tell the other boaters. Take names and publish on the
Internet. But don't throw out the safety net because even with corroded
connections, the wiring may still allow a ground fault to be cleared.

If there is a problem with a nearby source (boat or otherwise) then an
isolation transformer would be a good idea.

But even with an isolation transformer, always use approved wiring
practices. There is probably no more thoroughly reviewed standard than
the NEC. The ABYC standards for AC wiring are similarly solid.

And install GFCIs for the smaller ground fault currents that won't trip
a regular breaker but can electrocute.

Good luck.

Chuck



















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