Isolation ground transformers
Doug Salacia
sits in a 35 year old Marina near Houston, TX and in 3
months the zincs melted off! I have a big fish zinc that I
toss out whenever we are in the slip, the bonding system is
not perfect, but is there and working including a zinc in
the heat exchanger. The textbook answer (Nigel Calder) is
to get the bonding system and the 110V ground system into
good order and then put on an isolation ground transformer
on the shore power ground. This is about $100 to purchase,
but is also another piece of electrical gear to find room
for, wire up, and hope and pray it will never break down.
Does anybody have experience with these positive or
otherwise?
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Larry W4CSC
Shack and hook one lead to the ground lug on the boat cord. Hook the
other lead to the ground on the dock power box (the case of the box is
grounded). Set the meter to the DC amps range and downrange until you
see if there is any current flowing to or from the boat to marina
ground. See it? If you do, get someone to watch the meter, one of
your neighbors who's had enough with the zinc replacements, and go
down the dock unplugging one boat at a time. The offender's boat,
that piece of crap with lots of metal underwater and NO zincs, will
drop the current, bigtime, when you unplug HIS boat....or boats.
Have the marina notify him of his transgression and get him to buy him
a zinc fish!
The isolator does work great. Transformers are not a maintenance
headache, at all. There are 3 huge isolation transformers in the
auxiliary equipment compartment under the galley of my friend's
Hatteras 56. He needs zincs on the shafts about once a year.
larry
Twin Boat
wire after the shore power connector and wire in series. Went from 3 months to
full season on Zinks.
Doug Salacia
any other suggestions? It would help to know the
manufacturer. BTW, just because it is in the WM catalog
does not mean they will order it or deliver it - it took 4
tries to get them to ship me some packing box wrenches
which are shown in the catalog. The local store would not
order it, the catalog people said they were out of stock
and transferred my call to the manufacturer. Finally I
called again to the WM catalog number and got a competent
person who put the order in subject to back order filling.
In article <20000528091605...@ng-ff1.aol.com>,
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Twin Boat
but only one I see. Mine is made by" Yacht Corrosion Consultants Inc."
Jim Donohue
kick the master breaker if disconnected killing my charging systems where
upon the battery would take over the refrigeration which would drain the
batteries in a couple of days. After that no more bilge pumps. A friend's
boat has an auto start and transfer to generator on a power outage to
protect his freezers. He would get an automatic phone call about the
problem but would not be pleased that some *&^%(*^ idiot had disconnected
his shore power to check for ground leakage. He would try to have you
arrested or at least thrown out of the marina - and I think with just cause.
I suggest you consider the isolation transformer. There is no rule by the
way that it has to be on the boat. Build it into a dock step or such and
leave it ashore if most of your boating is done from the same marina. If
you get around a bit I would suggest figuring out how to get one on board.
I personally believe they should be required gear on all boats that can tie
to shore power - for safety reasons as well as the prevention of galvanic
corrosion.
The other gizmo discussed is called a galvanic isolator and can be found in
the WM catalog under that title. (Or at least in 1999 sailing edition).
The 30 amp version is about $128. I don't recommend them. They do not
provide the safety attributes of an isolation transformer and the layman
hasn't got a prayer of telling whether or not they are working.
Jim
Larry W4CSC <W4...@lostonthe.net> wrote in message
news:FA4841C4E41BD50F.5F5C5474...@lp.airnews.net...
Larry W4CSC
<jim_d...@computer.org> wrote:
>Let us be a little cautious here. My last boat for instance was likely to
>kick the master breaker if disconnected killing my charging systems where
>upon the battery would take over the refrigeration which would drain the
>batteries in a couple of days. After that no more bilge pumps. A friend's
>boat has an auto start and transfer to generator on a power outage to
>protect his freezers. He would get an automatic phone call about the
>problem but would not be pleased that some *&^%(*^ idiot had disconnected
>his shore power to check for ground leakage. He would try to have you
>arrested or at least thrown out of the marina - and I think with just cause.
Doesn't he get an autophonecall every time the lights blink? How's he
going to know the difference??
>
Besides, the dockmaster was the one helping us on the last zinc fiasco
I was on. HIS zincs were disappearing at an alarming rate, too! I'm
sure bitching at him might get YOU thrown out of the marina....(c;
Larry....I've never met anyone arrested for unplugging a boat,
momentarily. Have you?
Jim Donohue
crime. I do believe it might get you thrown out of a marina however. If
you went down "battleship" row in the Long Beach Marina disconnection each
boat in turn I would guarantee you a whole lot of alarms would go off, the
cops would get called, the marina staff would be on you on about the third
or fourth boat. Big boats do not like having their electric messed with.
I think the automatic waits a few minutes before deciding it is really
disconnected. If I remember the setup correctly the transfer to the
generator is entirely automatic but the reset to shore power is manual. He
has about a 50 mile round trip to get to the boat so you can expect him to
be annoyed.
Jim
Larry W4CSC <W4...@lostonthe.net> wrote in message
news:60235FC55DA2A0E8.85868F97...@lp.airnews.net...
Steve Weinagrt
animal as an 'Isolation ground transformer' there are two different devices,
a galvanic isolator, and an isolation transformer,
The galvanic isolator is just an assembly two very big back-to-back diodes
that make a barrier of about 0.600V (600 millivolts ) in the ground wire
between the shore and the boat (and we assume that the boat ground or green
wire goes all the way to metal that touches the water). The galvanic isolator
is ONLY for the purpose of protecting the underwater mteal on the boat from
galvanic corossion. This 600mV barrier is usually enough to prevent all but
the worst galvanic offense, it won't help much in cases of AC leakage. This is
not a safety device.
The isolation transformer breaks the DC path between the boat and the shore by
transformer coupling the AC. The boat's green is separated from the shore's
green (ground) wire. This is both a galvanic protection AND safety device.
The AC on a boat with an isolator is floating with respect to the shore so
that holding even a hot lead of the boat's AC service and touching shore
ground will not cause a shock hazard. The only way that you can complete the
circuit is from one of the boat's hot leads to it's own neutral/green (ground)
leads. This complete isolation gives the galvanic protection along with the
safety.
Just a final point, if you use shore power, install your own ground fault
interrupter (GFI), sooner or later, it will save someone from shock and
probably save their life.
Steve Weinagrt
[snip]
After re-reading this this moring and answering a question about it, let me
try again :-)
>The galvanic isolator is just an assembly two very big back-to-back diodes
>that make a barrier of about 0.600V (600 millivolts ) in the ground wire
>between the shore and the boat (and we assume that the boat ground or green
>wire goes all the way to metal that touches the water). The galvanic isolator
>is ONLY for the purpose of protecting the underwater mteal on the boat from
>galvanic corossion. This 600mV barrier is usually enough to prevent all but
>the worst galvanic offense, it won't help much in cases of AC leakage. This is
>not a safety device.
>
Small shifts in the shore GND line can cause the GND to not be truly earth, 0
volts. An offset of 200 - 300 mV driven by a non 0 V shore gnd will eat up
your underwater metal in no time. The offset GND being the electromotive
source and the underwater metal being the electrode. The +- 600 mV of
blocking that a galvanic isolator provides will stop the metal
erosion/corossion caused by small shore GND offsets..
I hope that this is clearer.
Cheers,
Steve
sven...@earthlink.net
Nigel Calder's book is correct. In the best of all worlds you should
sort out you safety & DC grounds. I sorted it out on my vessel (1988, 44
ft CC Morgan) but previous owners had not left me to much of a mess by the
time I got to it. So I can empathize with you if you are confronted by a
rats nest. But you need to bite the bullet and sort through it.
By the time you are done ALL DC grounds need to DEAD END at a bonding
block. All your AC safety grounds also need to dead end at one place.
Test the system by first disconnecting shore power. Then use an ohm meter
and measure the resistance between the AC safety, DC ground and AC neutral.
In this configuration you should see an open circuit resistance between all
three. NOW, connect a SINGLE wire of about 10 gauge between the AC safety
block and the DC block. That gives a dead short between them. AC neutral
& AC safety should be shorted on the dock once you plug back into shore
power. There should be NO short between them ANYWHERE on your vessel.
The isolation transformer is in fact the absolute best approach for
many reason that are not limited to zinc corrosion. But they are more
expensive, heavy, bulky and require competent design and installation.
Don't do this unless you really know what you are doing or have qualified
personnel do the design and actually do the installation. There is more to
it than just going down to your local salvage yard or electrical supply and
slapping the thing in the shore power line. We are going to put aboard a
7.5 kVA Cutler Hammer "export" transformer that will supply 6 kW @ 120V
from about 8 different input voltages ranging from 195 to 440 volts. Note
that kVA (transformer rating) IS NOT the same thing as kW.
The "zinc saver" isolator is a compromise, reasonable cost solution
that is easier to implement. If you have cleaned up your electrical system
first. The place you want to put the isolator is in that single 10 gauge
wire you added last between the AC safety & DC ground. Remember the one
you added just after you tested the system and saw opens between all three
legs. If placed in that position in a properly configured system you will
not have a problem if you properly add a generator later on.
Isolators can be implemented by using two types of electrical devices.
The pair of diodes connected head to tail has been mentioned. This is
essentially a small resister placed in the line. Called a diode drop in
the lingo. A more effective and equally safe device is a capacitor. This
device passes AC but is an open to DC. Meaning it is an AC device only, it
has no DC function. Using a capacitor will DC separate the two but leave
them AC connected if installed as described in the previous paragraph.
Your AC safety (green) will remain dead shorted to the pier. If you later
add a generator, only the hot (black) & neutral (white) are connected into
the ships AC system. Safety (green) is created via a heavy gauge jumper
from the generator end neutral (white) to the chassis frame. The DC ground
for the generators DC starting motor also connects to frame, back to the DC
bonding block which is AC connected to the AC safety (green) via the
isolator. So an AC hot (black) short to safety (green) will trip the
breaker by feeding back through the isolator to DC ground then to chassis
frame and on to generator neutral completing the circuit. But you will
still see a DC open between AC safety (green) & DC ground. If you do not
connect things up EXACTLY like this you will bypass (short around) the
isolator and defeat its function.
sven...@earthlink.net
descriptions. I want something from Guest I can rely on.
I have called Guest and am awaiting a call back from one of their
Engineers. I want to know EXACTLY what devices they have potted up in that
epoxy block they are selling. Also a schematic of how those devices are
connected up inside that block of epoxy. I will get back to you and post
an authoritative report from Guest of what and how their device works.
Generally however my system schematic descriptions holds true for both
Diode & Capacitor isolators. What you see on your ohm meter will be
different with a diode devices and can even vary depending on what type of
diode class device used. Believe it or not there are over a half dozen
solid state devices that are directly referred to with "diode/rectifier" in
their name or are called something else but are more or less variations on
the basic diode device.
BTW, my "dead end" descriptions my need polished. By a dead end point
I mean a point were all distributed lines from that point fan out.
Naturally there has to be a connection to that point that energizes or
grounds the fan out point from somewhere else. So calling is a "dead end"
has its weak points. But it does metaphorically describe it for purposes
of a vivid description.
Just for your amusement & amazement. The formula to determine the
size of the capacitor you will need in micofarads is
mf=(ampX2650)/volts. My main breakers trip at 30 amps with smaller load
breaker after them. To ensure a instantaneous trip on fault I used the
formula to determine the capacitor for 40 amps @ 120 volts requires 884 mf
of capacitors. That will ensure a trip somewhere in the system almost
instantly on a fault to AC safety (green) in any instance where the
capacitor must pass the AC to complete the circuit. This will happen on an
AC fault when the generator is carrying the load or on shore power if the
AC fault is to something connected to the DC ground side of the capacitor.
Like in the engineroom when using an AC power tool with all those DC
grounded engine blocks and other such things.
I used standard "start" capacitors for AC electric motors. The
largest I could easily find at local supply houses were 216 mf. So I got 4
of them and wired them up in parallel. They each cost about $25 or $100ish
dollars total in my case. The normal voltage for these sorts of caps is
240 volts.
Jim Donohue
any number of cases where there is some residual load in the circuit rather
than a true short. I would think the capacitor bank should be a factor of 5
or 10 times larger if you want a trip under these conditions. That is why
the technique is not used very often.
I think there is little support for galvanic isolators in general from the
tech side. They are reasonably easy to fail and show no indication when it
happens. You pretty much have to remove them from the circuit to test em.
Boats that plug into the power grid really should have isolation
transformers. However the boat manufacturers don't want to pay the price
and have to pass it on to the customer. So ABYC will not do the right
thing.
Jim
<sven...@earthlink.net> wrote in message
news:3938FE3C...@earthlink.net...
Steven Kennedy
Jim Donohue <jim_d...@computer.org> wrote in message
news:sji8ghs...@corp.supernews.com...
> Boats that plug into the power grid really should have isolation
> transformers. However the boat manufacturers don't want to pay the price
> and have to pass it on to the customer. So ABYC will not do the right
> thing.
>
> Jim
>
James
What does ABYC have to do with this? This is a totally voluntary standards
setting body. By that I mean that it is up to the individual boat builder
or owner to voluntarily comply with the standards. All of their literature
strongly encourages the use of isolation transformers. Yet, I have yet to
see a small boat mfr. "voluntarily" install one. ABYC also produces
standards for both of the products under discussion: marine isolation
transformers and galvanic isolators. Manufacturers still continue to
produce the cheap kind without capacitors.
ABYC is also aware that it needs to produce standards that will be adhered
to. As you can see by reading at this NG the world is full of people (some
brilliant, some nuts) who will ALWAYS chose the cheapest way; or with those
who ALWAYS know best. There are also those who as "hobbyists" go to any
length to "build their own" marine electrical or electronics components...as
well as encouraging others to do the same. Since boats are regarded by UL
and other such general, standards setting bodies, as appliances; our freedom
to continue these practices goes unabated. However, imagine if we all were
to wire our own homes with the knowledge and experience that we each
individually have, and our own narrow set of opinions. This is why
standards continue to be set, which though they may be narrow or limiting,
are in fact designed to save our lives and/or our boats. Are they
perfect...no. Are they constantly being considered and revised.....yes.
So, unless I missed a part of this thread that I shouldn't have, why is ABYC
at fault for these lame fools going to the very cheapest mfr. of marine
products instead of the best? Should we all demand schematics of all of our
marine electrical products...probably. Should we make our own galvanic
isolators....probably not. I'm very, very tired of "I'm an engineer"
offered as the answer to each problem. Here in Sillyclone valley the day
does not go by that I don't hear that, usually when defending some
lame-brained scheme of wiring a boat unsafely. Well, so am I (an engineer),
but what the hell does their experience in wafer fab. or ham radio have to
do with safe and efficient boat power wiring.........nothing...zip.
For instance earlier here the guy decided to "use a regular, non-marine"
isolation transformer. Bad idea...marine isolation xfmrs are NOT the same
as lighting type "regular" iso. xfmrs. It has to do with the ground (MOST
important) not to mention the cheap rust prone steel case (less important).
Please refer to the appropriate ABYC Standards sections. Saving your life is
THEIR business.
skennedy
Sinewave Marine Electric
ABYC Certified Marine Electrical Tech.
Jim Donohue
Steven Kennedy <sken...@earthlink.net> wrote in message
news:y5b_4.2087$Fe.6...@newsread2.prod.itd.earthlink.net...
>
> Jim Donohue <jim_d...@computer.org> wrote in message
> news:sji8ghs...@corp.supernews.com...
>
> > Boats that plug into the power grid really should have isolation
> > transformers. However the boat manufacturers don't want to pay the
price
> > and have to pass it on to the customer. So ABYC will not do the right
> > thing.
> >
> > Jim
> >
>
> James
>
> What does ABYC have to do with this? This is a totally voluntary
standards
> setting body. By that I mean that it is up to the individual boat builder
> or owner to voluntarily comply with the standards. All of their
literature
> strongly encourages the use of isolation transformers. Yet, I have yet to
> see a small boat mfr. "voluntarily" install one. ABYC also produces
> standards for both of the products under discussion: marine isolation
> transformers and galvanic isolators. Manufacturers still continue to
> produce the cheap kind without capacitors.
The primary electrical systems shown and therefore promoted by ABYC are done
both with and without isolation transformers. This is an endorsement from
ABYC that such circuits are acceptable. The ABYC requirements should
simply require them for both safety and performance reasons. The
manufacturer can then volunarily not comply but I suspect the boats would be
uninsurable. The internals of ABYC make such a policy position unlikely on
grounds that have nothing to do with safety.
ABYC is voluntary unless you need a survey or to pass a coast guard
inspection where upon it becomes a requirement. UL is similarly volunteer
unless you want your equipment used in offices in Chicago or New York
whereupon it becomes legally required.
The isolation transformer spec of ABYC has only one pecuiliar clause dealing
with the ability of the shield to handle heavy fault currents. This, and
this only, differentiate ABYC isolation transformers from others. The
result is a sole source part that is sold at a significant premium.
The technical argument for the heavy shield is weak. It does provide a
slightly better protection for one winding but really does nothing for the
other. So you have a deal where you pay a premium price to protect half the
load against an unlikely failure. A solid ground to the case is probably
all that is actually needed.
I think ABYC walks a tricky line. They clearly have some role as a safety
standard setting agency. They are very concerned with electrocution in the
water near boats. At the same time they carry a large brief for the
industry and resist safety requirements that they should advocate. They
advocate safety but not at the cost of establishing voluntary standards that
would not include present industry standard practice.
>
> For instance earlier here the guy decided to "use a regular, non-marine"
> isolation transformer. Bad idea...marine isolation xfmrs are NOT the same
> as lighting type "regular" iso. xfmrs. It has to do with the ground (MOST
> important) not to mention the cheap rust prone steel case (less
important).
As I said above there is no significant difference between marine and
outdoor for the isolation transformer other than the shield. I think he
will do fine. I had mine installed in my dockstep as I lacked a good place
aboard. I was certainly within ABYC as the islolation transformer was not
on the boat. It would, however, have worked equally well even if it was.
>
> Please refer to the appropriate ABYC Standards sections. Saving your life
is
> THEIR business.
That is exactly the point - should be but isn't always.
Jim ( I think I will get ABYC certified one of these days so I can put it in
my sig too. )
sven...@earthlink.net
circumstance. You either have a short to safety or you do not. Either the
breaker trips or it does not. Safety ground does not provide protection for
resistive shorts only overload shorts, with or without an isolator present.
Put more bluntly, If your body is the resistive short, the breaker is not there
to protect you. Breakers protect wire, GFI protects people. Yes all my AC
circuits aboard are GFI protected.
Once the breaker trips AC ceases and the capacitor is an open, so 5X 10X
100X 1000X of cap size is irrelevant. Any residual charge would be of a DC
nature and would dissipate in microseconds. In fact the larger cap would only
increase the RC (Resister Capacitor) time constant and hold any "residual DC
charge" longer.
I am more than willing to be proven wrong however. Give me facts, figures
& explicit description of the circuit and I will consider the problem. Keep
supposition, opinion, guesses, vague generalities & politics to yourself. Give
me engineering facts and we will either find an engineering & mathematically
provable answer or disprove the model submitted. Not a bunch of lip flapping
and jaw jacking suppositions.
Jim Donohue wrote:
> You sure you are doing that calculation correctly? There are likely to be
> any number of cases where there is some residual load in the circuit rather
> than a true short. I would think the capacitor bank should be a factor of 5
> or 10 times larger if you want a trip under these conditions. That is why
> the technique is not used very often.
>
>
>
> Jim
Jim Donohue
out here where you will infect others. You obviously know very little about
circuits, about breakers, about electrical fires or safety in general. Why
waste your time here - Go experiment privately and let Darwin decide.
Jim
<sven...@earthlink.net> wrote in message
news:393A98E9...@earthlink.net...
> > You sure you are doing that calculation correctly? There are likely to
be
> > any number of cases where there is some residual load in the circuit
rather
> > than a true short. I would think the capacitor bank should be a factor
of 5
> > or 10 times larger if you want a trip under these conditions. That is
why
> > the technique is not used very often.
> >
> >
> >
> > Jim
>
sven...@earthlink.net
the JAXAsby clown. If you have a point, make it. With facts, not rhetoric.
Lets hear some of your understanding I am missing, "about circuits, about
breakers, about electrical fires or safety in general." Share your knowledge
with us in a rational thesis.
Here are some facts. It would take a 4 ohm resistive short to raise the
safety to 50 volts across a 120 volt circuit through a 864 mf capacitor to
earth. That would yield a 16 amp current with a 70 volt drop across the
resistor. Now in that circuit, the resistor would be dissipating an
instantaneous load of 1.1kW. Assuming that the GFI didn't notice all that
return neutral current missing and trip. The resistor would have to be a
ceramic or tungsten or it would act like a fuse and open itself. Your average
15 amp breaker would not trip immediately in this situation so it wouldn't
protect you or prevent a fire.
Now lets remove the cap and redo all this with the same 16 amps. It would
now take a 7.5 ohm resistive short across a 120 volt circuit to safety, which
in this case IS earth. Same 1.1 kW instantaneously dissipating across the
load. The 15 amp breaker would still take a few moments to trip, you could
still be just as dead, the fire could still happen.
I have rerun the model with larger & smaller resistive shorts and it keeps
turning out the same way. The 864 cap in safety just doesn't matter. By the
time the resister reaches 34 ohms, current is down to 3 to 4 amps with or
without the cap. In the 34 ohm model safety is at 10 volts with the cap. A
resistive short that WOULD cause injury or fire WILL cause that injury or fire
with or without the 864 mf cap in the circuit. A resistive short that WOULD
NOT cause injury or fire WILL NOT cause that injury or fire with or without the
864 mf cap in the circuit.
Maybe I have buggered my calculations. If I have, please point out my
error. I will gladly apologize and acknowledge any factal errors. I have been
know to make mistakes.
Jim Donohue wrote:
> If you want to do idiot power circuit design - go do it. But don't put it
> out here where you will infect others. You obviously know very little about
> circuits, about breakers, about electrical fires or safety in general. Why
> waste your time here - Go experiment privately and let Darwin decide.
>
> Jim
> <sven...@earthlink.net> wrote in message
> > > You sure you are doing that calculation correctly? There are likely to
> be
> > > any number of cases where there is some residual load in the circuit
> rather
> > > than a true short. I would think the capacitor bank should be a factor
> of 5
> > > or 10 times larger if you want a trip under these conditions. That is
> why
> > > the technique is not used very often.
> > >
> > >
> > >
> > > Jim
> >
Jim Donohue
conflict? Give me some section numbers so I can look them up.
The subject of the discussion was galvanic isolation. I see nothing in your
discussion that deals with that subject. I don't see anything I disagree
with except, perhaps, as alluded to in the first paragraph. But lets see
what you got on it .
Further I know of no spec that reads on capacitive galvanic isolators in
either code. If that is true then we are dealing in areas of engineering
not code. In fact even if done properly it may well violate code.
By the way a sure way to discover someone with a personality problem is to
find someone who points out those of others.
Jim
Lew Hodgett <lewho...@earthlink.net> wrote in message
news:393AF3C9...@earthlink.net...
> Without getting into the middle of a pissing contest which appears to
> be filled with comments of those who appear to definitely have
> personal problems, let me offer the following:
>
> First of all, let's establish something.
>
> Have spent many years in the design, application, and sale of
> electrical distribution systems and utilization equipment.
>
> You can do what ever you choose with that information.
>
> Now, on with the show.
>
> By definition, the NEC defines a circuit protective device, be it
> c'bkr or fuse, has having only one task, that is to protect the
> insulation on the conductors that are connected to it, period, end of
> report.
>
> As long as the current flows within the defined path, and is within
> the limits of the circuit protective device, the circuit protective
> device will not (better not) trip.
>
> Only if the current flows outside the defined path will the circuit
> protective device function.
>
> For instance, if the toaster on your kitchen counter, develops a
> problem, and starts to smoke, as long as the current flowing is within
> the limits of the circuit design, the circuit protective device will
> not trip, even if the toaster should catch on fire.
>
> There are other devices required to address that issue, as well as
> those for protecting people.
>
> The bottom line:
>
> When it comes to circuit protective devices, the NEC doesn't give a
> hoot about anything but the insulation on the conductors being
> protected by the circuit protective device.
>
> How does all that relate to boats?
>
> The grounding specifications defined by NEC and ABYC for vessels are
> in DIRECT CONFLICT with one another, primarily based on the fact that
> address totally different conditions, but on the same boat.
>
> If you are plugged into shore power, you MUST comply with NEC. There
> are no exceptions.
>
> If you are at sea operating from a generator, you better comply with
> ABYC which is in direct conflict with NEC.
>
> The only way to safely meet both sets of conditions, is to install an
> isolation transformer for the shore power and a transfer switch for
> the generator.
>
> About $500 plus installation, and a 100 lbs, you get a 5KVA x'fmr, and
> you sleep soundly.
>
> The x'fr switch is a separate issue.
>
> Don't want to spend $500 or add 100 lbs, seriously consider not
> installing permanent AC wiring on your boat. Use an extension instead
> to fire that electric skillet.
>
> HTH
>
>
> Lew
>
> S/A: Challenge (Under Construction, the hull is turned in the
> Southland)
>
> Visit:<http://home.earthlink.net/~lewhodgett> For Pictures
>
> There are no problems, only varying degrees of challenging
> opportunity.
Jim Donohue
8.20.2.3 - specify a set of requirements that cannot be met by a capacitive
isolator. Basically a voltage drop of 2.5 volts at rated current is
required and 3 repetitions of a 5000 amp RMS short circuit test. While such
a device can be theoretically defined it cannot be practically made. We
will leave the calculation of the required impedances to the student.
We are therefore in an engineering discussions of a device that clearly
could not meet the normal spec. and would certainly fail survey.
I think there are two other considerations. I think the maintenance of safe
voltage levels on exposed devices is still a practical requirement. While
GFI should be the primary defense a ground system that protects against
failures to shields and covers is an important redundant capability. Ones
life should not hang on a GFI interrupter.
I think however a primary use is to avoid electrical fires caused by the
breakdown of some insulator in the system. While one can project parameters
that may sustain a fire in some particular device the addition of any
significant series impedance will make the problem worse. Hence the ABYC
spec which is designed to prevent the use of a device with any significant
voltage drop in the ground system. I think it particularly important that
currents at or exceeding the ampacity of the wiring cause a quick trip. The
addition of capacitive reactance in the size range discussed must greatly
increase the probability of such a situation given the characteristics of
many breakers.
Engineering is often a game of good enough - but you do need to play it
carefully. One has to be particularly careful of solutions that might work.
I would think that some full scale probablistic analysis of the likely
parameters would be needed to arrive at a precise number. ABYC takes the
classic engineering out of requiring a low enough number that its impact may
be ignored - thereby escaping the close to impossible determination of the
correct number.
Jim
Marcus G Bell <be...@mail.med.upenn.edu> wrote in message
news:8hevlo$28l$1...@netnews.upenn.edu...
>
> OK, at 60 Hz, the equivalent impedance of an 884 uf (that's uf for
> microfarads, not mf for millifarads, call me old school) capacitor
> is 3 ohms (that's 1/{jwC}, and yes, it's a reactive load so maybe
> we need power factor corrections when it's in series with other
> things but we're getting within the right ballpark).
>
> That 3 ohms is between the boat's safety ground and "true earth".
> If we have a "dead short" of the 120 VRMS AC supply to safety
> ground on the boat, we pass 120 VRMS through that 3 ohms, and get
> 40 amps. All fine and good it will trip the breaker at some point,
> but during the time before the breaker trips, safety ground is
> "lifted" to a large fraction of the 170 peak volts for parts of
> the cycle.
>
> It would really suck if I happened to be touching the boat's
> safety ground during that time (I form a capacitor with the earth
> beneath me, so I charge and discharge with every cycle), and it
> would suck worse if I were holding onto something bonded to the
> boat's safety ground while I was in contact with the earth (like
> wading behind the boat working on the prop on the metal propshaft
> connected through the engine to the AC safety ground, but there
> are plenty of other scenarios).
>
> Now, how long does it take the typical supply breaker to trip at a
> 133% load, which is what 40 amps is relative to the 30A breaker
> rating? It's probably a few seconds; the fastest magnetic types I
> can find specs for in my Newark catalog range 5 to 50 seconds at
> 150% of rated load (it's a statistical and logarithmic thing), but
> I haven't looked at all the specs of all the breakers in all the
> other catalogs so I'll keep it at a "few seconds" anyway instead
> of averaging up to 15 or whatever. It's still too long.
>
> Let's consider the impedance of the supply and safety ground in
> the more typical "at home" situation, without a capacitive
> isolator in place. Could we allow that a liberal estimate of
> safety ground is about 1/10th of an ohm, or about the same as the
> impedance of the "hot" line but probably not much more? OK,
> continuing, if hot shorts to ground, ground gets lifted to about
> 60V at the point of the short (voltage divider effect), but back
> at the breaker it's 120V/0.2ohm=600 amps, and the 30A breaker
> trips purty toot sweet at 2000% load (pardon my french), so that
> 60V doesn't last very long.
>
> Next, let's have a fault where neutral breaks inside an appliance
> and the load's neutral contacts the grounded metal case, and it's
> a resistive load of 6 ohms like a heater or something. That's
> 120V/6.2ohms = 19.4 amps (I added the impedance of the hot and
> ground). The main 30A breaker will never trip on this current, and
> even a 20 amp breaker on a branch circuit would take hours to days
> to trip. However, the 19.4 amps through the 0.1 ohm safety ground
> will lift it to 1.9 volts RMS. That's pretty innocuous to most
> living creatures that would come in contact with it, so safety
> ground is doing its job of shunting the fault current to ground
> and protecting life.
>
> Now, let's go back and add our 3 ohm "galvanic isolator" in the
> ground path on the boat, and now we've got 120V/9.2ohms = 13 amps.
> Again, no breakers trip. But now we've got 13 amps running through
> a 3.1 ohm ground path, so safety ground is lifted to 40 volts.
> Kiss your zincs goodbye and very possibly some poor creature that
> bridges the gap between safety ground and earth.
>
> In these failure modes, a GFCI would have quickly detected the
> imbalance between neutral and hot and shut down the supply, and
> risk to life would have been lessened. In this regard, GFCI's have
> rendered safety ground somewhat superfluous. Nevertheless, we
> haven't given up on safety ground, perhaps because GFCI's are not
> failure-proof and we still want something simple and robust as a
> last defense against premature passage to that marvelous marina in
> the sky.
>
> Safety ground is a bit more than protection for dead shorts; it's
> protection against a fault lifting an exposed conductor well
> enough above ground potential so as to be lethal if touched. That
> means it does in fact protect against "resistive shorts" of the
> type described above. Placing a device in the ground path which by
> design could allow the ground to achieve high voltage for seconds
> to days on end is not very different in concept from disconnecting
> the ground altogether.
>
> Based on engineering analysis, I have to agree that a capacitive
> isolator should be sized to pass several times the main breaker
> current so as to trip the breaker as soon as possible. Even if the
> breaker were to fail to trip in that situation, the resultant
> voltage at safety ground would be kept to a far lower value than
> would be the case if the capacitor's impedance were a full order
> of magnitude above that of the mains supply wiring.
>
> -- -- Marcus. ( be...@mail.med.upenn.edu )
Lew Hodgett
Marcus G Bell
> formula to determine the size of the capacitor you will need in
> micofarads is mf=(ampX2650)/volts. My main breakers trip at 30
> amps with smaller load breaker after them. To ensure a
> instantaneous trip on fault I used the formula to determine the
> capacitor for 40 amps @ 120 volts requires 884 mf of capacitors.
>
> Jim Donohue wrote:
> > You sure you are doing that calculation correctly? There are
> > likely to be any number of cases where there is some residual
> > load in the circuit rather than a true short. I would think
> > the capacitor bank should be a factor of 5 or 10 times larger
> > if you want a trip under these conditions. That is why the
> > technique is not used very often.
sven...@earthlink.net wrote:
> Frankly no, I don't see any case at all where this is likely
> under any circumstance. You either have a short to safety or you
> do not. Either the breaker trips or it does not. Safety ground
> does not provide protection for resistive shorts only overload
> shorts, with or without an isolator present. ... Keep
> supposition, opinion, guesses, vague generalities & politics to
> yourself. Give me engineering facts and we will either find an
> engineering & mathematically provable answer or disprove the
> model submitted. Not a bunch of lip flapping and jaw jacking
> suppositions.
OK, at 60 Hz, the equivalent impedance of an 884 uf (that's uf for
Marcus G Bell
> The bottom line: When it comes to circuit protective devices,
> the NEC doesn't give a hoot about anything but the insulation on
> the conductors being protected by the circuit protective
> device.
> How does all that relate to boats? The grounding specifications
> defined by NEC and ABYC for vessels are in DIRECT CONFLICT with
> one another, primarily based on the fact that address totally
> different conditions, but on the same boat.
What do each of the grounding specifications say that grounding is
supposed to do? Is grounding simply to preserve the insulation on
the hot and neutral as a circuit protective device, or is there
some other function?
Marcus G Bell
> Going a little further the ABYC specs -see E8 sections 8.20.2
> through 8.20.2.3 - specify a set of requirements that cannot be
> met by a capacitive isolator. Basically a voltage drop of 2.5
> volts at rated current is required and 3 repetitions of a 5000
> amp RMS short circuit test.
Hmmm, what do we mean by "rated current"? Safe enough to assume
that's the breaker spec? OK, to get the 60 Hz impedance for a 2.5
volt drop at 30 amps, we need at least a 32,000 microfarad
nonpolarized capacitor. A 33,000 uF polarized electrolytic with a
50VDC rating would be about the size of a beer can, while a
nonpolarized 120 uF 240VAC cap is about the same size. We need 267
of them to run in parallel. That's a lot of beer cans.
Now, a 5000A RMS test? We're going to have to supply about 400 V
RMS to perform that one, if that's 60 Hz. Ooops, that might exceed
the rating of the capacitors and they'll go poof, better switch to
the 440 VAC variety. They're 70 uF per can, so we'll need 458 of
them. Did I mention these run about 50 to 75 dollars each?
> While such a device can be theoretically defined it cannot be
> practically made. We will leave the calculation of the required
> impedances to the student.
No, we'll just do them right here ;-)
Lew Hodgett
>
> OK I'll bite. Where are the grounding specs of ABYC and NEC in direct
> conflict? Give me some section numbers so I can look them up.
>
> The subject of the discussion was galvanic isolation. I see nothing in your
> discussion that deals with that subject.
The NEC allows only one earth ground termination located at the
service entrance point, for any service.
The ABYC requires that the earth ground on board for a vessel be
grounded essentially to the water by means of connection to the hull
if steel, or the engine block.
This creates a 2nd ground point for the shore power service which is
in direct violation of NEC and can also create galvanic bleed currents
that will consume zincs with glee.
The only solution is an isolation x'fmr which now treats the vessel
wiring as a new service entrance, thus allowing a new earth ground to
be established.
An isolation x'fmr not only provides increased safety, complies with
NEC, it also minimizes galvanic currents created by improper AC shore
power installations that have the shore power earth ground incorrectly
connected to the boat.
Find a so called "hot boat" in a marina, and the chances are very good
that the shore power earth ground is imprpoerly connected.
Jim Donohue
is referred to as the grounded neutral. ABYC E8 8.5.2.1 says
"The shore power neutral is grounded through the shore power cable and shall
not be grounded on the boat. "
The next clause requires grounding the neutral of an isolation transformer
secondary - a very strange piece of unsafety engineering but the basic
grounded ac line is never grounded on the boat.
All ABYC sample hooks up in Appendix A also maintain this seperation. Note
also that the grounded neutral is always switched in single phase hookups.
The green safety wire is grounded on the boat - just as it may be at many
points in the house.
I see no conflict between this and the NEC. I do not think there would be
very many marinas operating is it were true - at least not with shore power.
Jim
Lew Hodgett <lewho...@earthlink.net> wrote in message
news:393B228E...@earthlink.net...
Marcus G Bell
> Naw - Don't think so. May be a semantics problem. The white wire
> on a boat is referred to as the grounded neutral. ABYC E8
> 8.5.2.1 says
> "The shore power neutral is grounded through the shore power
> cable and shall not be grounded on the boat. "
That's very much like the (NEC or maybe local code) requirement
that neutral (white) be bonded to ground at the main panel, but
nowhere else. If you have a subpanel, you run your hot(s),
neutral, and ground separately, for neutral is not bonded to
ground at the subpanel. This is unlike the service entrance to the
main panel which has neutral and ground as one in the same
conductor. Branch circuits are like a subpanel, i.e. neutral and
ground are always separate (excepting the rare dedicated appliance
feed like a 240V hot water heater which has no real need for
neutral). The boat's electrical system is thus treated as if it's
just another subpanel or branch circuit, because that's in fact
what it is.
> The next clause requires grounding the neutral of an isolation
> transformer secondary - a very strange piece of unsafety
> engineering but the basic grounded ac line is never grounded on
> the boat.
If isolated neutral (white) and safety ground (green) are not to
be joined on the boat, then isolated neutral is free to "float" at
almost any potential with respect to earth. That's no good, as
many appliances have polarized plugs and assume that neutral is at
least pretty close to earth potential. So isolated neutral has to
be referenced to earth somewhere, and ABYC seems to be doing just
what NEC does, bond the neutral to earth at the transformer
secondary.
> All ABYC sample hooks up in Appendix A also maintain this
> seperation. Note also that the grounded neutral is always
> switched in single phase hookups.
Switched neutral? I'm guessing because we don't want to see even
the few volts that unbalanced single phase systems may have on
their neutral, when we shut of power to work on a circuit in a wet
environment.
> The green safety wire is grounded on the boat - just as it may
> be at many points in the house.
Yep, it's attached to earth at your main panel, maybe a subpanel,
maybe at your meter, almost definitely back at the transformer on
the pole, at the main panel of your neighbor's house, at some cold
water pipes somewhere in your house, etc.
Marcus G Bell
> Here are some facts. It would take a 4 ohm resistive short to
> raise the safety to 50 volts across a 120 volt circuit through a
> 864 mf capacitor to earth. That would yield a 16 amp current
> with a 70 volt drop across the resistor. Now in that circuit,
> the resistor would be dissipating an instantaneous load of
> 1.1kW. Assuming that the GFI didn't notice all that return
> neutral current missing and trip. The resistor would have to be
> a ceramic or tungsten or it would act like a fuse and open
> itself.
Why assume that the resistive short is an actual ceramic resistor
purchased from an electronic shop? Why can't it be just an
appliance representing a 4 ohm impedance, an appliance designed to
dissipate that 1.1 kW as part of its normal function without
starting a fire? That is a very common failure mode.
> Your average 15 amp breaker would not trip immediately in this
> situation so it wouldn't protect you or prevent a fire.
> Now lets remove the cap and redo all this with the same 16 amps.
> It would now take a 7.5 ohm resistive short across a 120 volt
> circuit to safety, which in this case IS earth. Same 1.1 kW
> instantaneously dissipating across the load. The 15 amp breaker
> would still take a few moments to trip, you could still be just
> as dead, the fire could still happen.
I think you'll be less dead if your safety ground doesn't get
lifted to 50 volts. Your 50V safety ground may find other paths to
earth and in so doing start fires away from the original fault,
fires that wouldn't have happened if safety ground were rigorously
clamped to be near earth potential.
> I have rerun the model with larger & smaller resistive shorts
> and it keeps turning out the same way. The 864 cap in safety
> just doesn't matter. By the time the resister reaches 34 ohms,
> current is down to 3 to 4 amps with or without the cap. In the
> 34 ohm model safety is at 10 volts with the cap.
Run the figures for a "zero ohm" short protected by a 20 or 30 amp
breaker, as I did. What voltage at safety ground did you arrive
at?
> A resistive short that WOULD cause injury or fire WILL cause
> that injury or fire with or without the 864 mf cap in the
> circuit. A resistive short that WOULD NOT cause injury or fire
> WILL NOT cause that injury or fire with or without the 864 mf
> cap in the circuit.
I disagree. There are all kinds of "safe" resistive shorts that
would not cause injury or fire if safety ground were held at earth
potential, but any number of problems in allowing safety ground to
exceed a few volts above earth.
> Maybe I have buggered my calculations. If I have, please point
> out my error. I will gladly apologize and acknowledge any factal
> errors. I have been know to make mistakes.
I think the error is not in calculation, but in your
interpretation of the risk in having an "extremely live ground".
Your 884 uF capacitor will not pass code because of that risk.
Jim Donohue
Marcus G Bell <be...@mail.med.upenn.edu> wrote in message
news:8hgfid$mvd$1...@netnews.upenn.edu...
>
> If isolated neutral (white) and safety ground (green) are not to
> be joined on the boat, then isolated neutral is free to "float" at
> almost any potential with respect to earth. That's no good, as
> many appliances have polarized plugs and assume that neutral is at
> least pretty close to earth potential. So isolated neutral has to
> be referenced to earth somewhere, and ABYC seems to be doing just
> what NEC does, bond the neutral to earth at the transformer
> secondary.
Actually 240 volt stuff is not referenced to ground and does not seem to
cause a large problem. Also europe manages to stand their appliances
floating. As a practical matter I don't think hot chassis design has been
done in the US in a long time. I would point out that the first failure in
a system without a tie to ground merely moves you to the same conditions you
would have with with a tied system. Thus you get one additional failure for
free. Note also that boats always switch both sides of single phase
circuits because of uncertain as to which is actually hot or that the
neutral may be hot because of all the interesting pecuilarities of marine
systems.
I think there are significant advantages to an ungrounded ac in terms of
maintenance and safety. The ABYC clause is a knee jerk sort of clause I
think designed more to keep it all familiar to techs than for safety. Note
that one can now verify the seperation of AC and DC with an VOM. It has
the additional advantage of keeping all the junk from the AC systems off the
DC busses.
>
> > All ABYC sample hooks up in Appendix A also maintain this
> > seperation. Note also that the grounded neutral is always
> > switched in single phase hookups.
>
> Switched neutral? I'm guessing because we don't want to see even
> the few volts that unbalanced single phase systems may have on
> their neutral, when we shut of power to work on a circuit in a wet
> environment.
>
> > The green safety wire is grounded on the boat - just as it may
> > be at many points in the house.
>
> Yep, it's attached to earth at your main panel, maybe a subpanel,
> maybe at your meter, almost definitely back at the transformer on
> the pole, at the main panel of your neighbor's house, at some cold
> water pipes somewhere in your house, etc.
>
Steven Kennedy
my reply....oops sorry..got sort of hung up there.
Once again, I find myself mostly agreeing with Jim (must be that irish
thing).
Firstly..as to Lews abusive post. Proves my point precisely. He knows
everything because he knows the NEC. Although I've spent over 20 years w/
it he knows. So fine, but the NEC coinsiders your boat an appliance, just
like the electric skillet he posted. As long as the boat deos not provide:
a short, an overload or a ground fault...then the NEC doesn't care what it
is.
The ABYC itself is not pure, perfect or complete. It is however what we
have to keep people who believe they know everything from harming temselves
or their "appliances".
skennedy
Steven Kennedy
> > Naw - Don't think so. May be a semantics problem. The white wire
> > on a boat is referred to as the grounded neutral. ABYC E8
> > 8.5.2.1 says
>
> > "The shore power neutral is grounded through the shore power
> > cable and shall not be grounded on the boat. "
>
> That's very much like the (NEC or maybe local code) requirement
> that neutral (white) be bonded to ground at the main panel, but
> nowhere else. If you have a subpanel, you run your hot(s),
> neutral, and ground separately, for neutral is not bonded to
> ground at the subpanel. This is unlike the service entrance to the
> main panel which has neutral and ground as one in the same
> conductor. Branch circuits are like a subpanel, i.e. neutral and
> ground are always separate (excepting the rare dedicated appliance
> feed like a 240V hot water heater which has no real need for
> neutral). The boat's electrical system is thus treated as if it's
> just another subpanel or branch circuit, because that's in fact
> what it is.
>
would treat them also. However such conditions do not exist on land.
> > The next clause requires grounding the neutral of an isolation
> > transformer secondary - a very strange piece of unsafety
> > engineering but the basic grounded ac line is never grounded on
> > the boat.
>
> If isolated neutral (white) and safety ground (green) are not to
> be joined on the boat, then isolated neutral is free to "float" at
> almost any potential with respect to earth. That's no good, as
> many appliances have polarized plugs and assume that neutral is at
> least pretty close to earth potential. So isolated neutral has to
> be referenced to earth somewhere, and ABYC seems to be doing just
> what NEC does, bond the neutral to earth at the transformer
> secondary.
>
> > All ABYC sample hooks up in Appendix A also maintain this
> > seperation. Note also that the grounded neutral is always
> > switched in single phase hookups.
>
> Switched neutral? I'm guessing because we don't want to see even
> the few volts that unbalanced single phase systems may have on
> their neutral, when we shut of power to work on a circuit in a wet
> environment.
>
This has more to do with idiots reversing polarity.
skennedy
Steven Kennedy
wording. Gounded conductor is NOT the same as Grounding conductor.
skennedy
Marcus G Bell <be...@mail.med.upenn.edu> wrote in message
news:8hf0lq$28l$2...@netnews.upenn.edu...
Marcus G Bell
> I think right here we need to insert a touch of sanity in
> regards to ABYC wording. Gounded conductor is NOT the same as
> Grounding conductor.
Right, one's a gerund, the other's a participle ;-)
Marcus G Bell
> > even the few volts that unbalanced single phase systems may
> > have on their neutral, when we shut of power to work on a
> > circuit in a wet environment.
Steven Kennedy (sken...@earthlink.net) wrote:
> This has more to do with idiots reversing polarity.
I think Jim mentioned this, but thanks for driving it home. The
idiot factor is not to be underestimated.
Steven Kennedy
not burn to the waterline if your theoretical musings are incorrect.
There are in fact comprimises made in all standards. This is not particular
to either the nec or abyc.
While you and I are squatting here inside, at our computers, not our helms
demanding that any safety measure be made absolute, most boaters are
outside, on the water, putting around in grossly unsafe boats, by OUR
"standards". Ones that were not built even to ABYC standards nor were they
maintained or repaired to those standards. On the other hand, boat builders
(however bad you consider them to be) have to build boats to a "price point"
which provides them with a profit of some kind. So naturally they wish to
do as little as they can consistant with the standards, and/or their lawyers
interpretations of the standards. Not my choice...just the facts.
I personnally am about to purchase a boat that costs so much that I'm going
to have to sell a home in SF to purchase it. One of the major reasons I'm
chosing to do this is because I know the incredibly high standards to which
this boat is built (and wired). I don't want to spend the next three years
reengineering all of the systems after I purchase it. I think unless each of
us can and will do the same, then we need to start making more positive
contributions to the standards that do exist; rather than grousing
childishly. Don't expect Catalina or Beneteau to keep to standards without
pressure.
Join ABYC and participate.
skennedy
Sinewave Marine Electric
ABYC CERTIFIED Marine Electrical Tech.
Lew Hodgett
<snip>
> Note here that generators and invertors are treated differently than the NEC
> would treat them also. However such conditions do not exist on land.
<snip>
Really.
Guess all those engine-generator sets complete with emergency stand by
transfer switches found all over the country don't count.
sven...@earthlink.net
not inflammatory. Marcus and Lew rose to the occasion magnificently and
in
the finest spirit of peer review. You lead with your brain not with your
mouth, bravo.
You rendered clear and cogent models that made me think and
uncovered
valid weakness in my model. That is how it is supposed to work.
Lew Hodgett wrote:
> Without getting into the middle of a pissing contest which appears to
> be filled with comments of those who appear to definitely have
> personal problems, let me offer the following:
>
> First of all, let's establish something.
>
> Have spent many years in the design, application, and sale of
> electrical distribution systems and utilization equipment.
>
> You can do what ever you choose with that information.
>
> Now, on with the show.
>
> By definition, the NEC defines a circuit protective device, be it
> c'bkr or fuse, has having only one task, that is to protect the
> insulation on the conductors that are connected to it, period, end of
> report.
>
> As long as the current flows within the defined path, and is within
> the limits of the circuit protective device, the circuit protective
> device will not (better not) trip.
>
> Only if the current flows outside the defined path will the circuit
> protective device function.
>
> For instance, if the toaster on your kitchen counter, develops a
> problem, and starts to smoke, as long as the current flowing is within
> the limits of the circuit design, the circuit protective device will
> not trip, even if the toaster should catch on fire.
>
> There are other devices required to address that issue, as well as
> those for protecting people.
>
> The bottom line:
>
> When it comes to circuit protective devices, the NEC doesn't give a
> hoot about anything but the insulation on the conductors being
> protected by the circuit protective device.
>
> How does all that relate to boats?
>
> The grounding specifications defined by NEC and ABYC for vessels are
> in DIRECT CONFLICT with one another, primarily based on the fact that
> address totally different conditions, but on the same boat.
>
> If you are plugged into shore power, you MUST comply with NEC. There
> are no exceptions.
>
> If you are at sea operating from a generator, you better comply with
> ABYC which is in direct conflict with NEC.
>
> The only way to safely meet both sets of conditions, is to install an
> isolation transformer for the shore power and a transfer switch for
> the generator.
>
> About $500 plus installation, and a 100 lbs, you get a 5KVA x'fmr, and
> you sleep soundly.
>
> The x'fr switch is a separate issue.
>
> Don't want to spend $500 or add 100 lbs, seriously consider not
> installing permanent AC wiring on your boat. Use an extension instead
> to fire that electric skillet.
>
> HTH
>
>
Marcus G Bell
> > Note here that generators and invertors are treated
> > differently than the NEC would treat them also. However such
> > conditions do not exist on land.
> <snip>
Lew Hodgett (lewho...@earthlink.net) wrote:
> Really. Guess all those engine-generator sets complete with
> emergency stand by transfer switches found all over the country
> don't count.
OK, then I'll ask.
How are all those engine-generator sets complete with emergency
stand by transfer switches found all over the country treated by
the NEC differently from the way ABYC treats the analogous system
in a boat? How are all those engine-generator sets complete with
emergency stand by transfer switches found all over the country
treated by the NEC the same as the way ABYC treats the analogous
system in a boat?
Please have your urine samples back to me by 5 ;-)
Steven Shelikoff
>
> > Steven Kennedy wrote: <snip>
> > > Note here that generators and invertors are treated
> > > differently than the NEC would treat them also. However such
> > > conditions do not exist on land.
> > <snip>
>
> Lew Hodgett (lewho...@earthlink.net) wrote:
> > Really. Guess all those engine-generator sets complete with
> > emergency stand by transfer switches found all over the country
> > don't count.
>
> OK, then I'll ask.
>
> How are all those engine-generator sets complete with emergency
> stand by transfer switches found all over the country treated by
> the NEC differently from the way ABYC treats the analogous system
> in a boat? How are all those engine-generator sets complete with
> emergency stand by transfer switches found all over the country
> treated by the NEC the same as the way ABYC treats the analogous
> system in a boat?
Forget all that. Did you hear that the code says you now have to
install 3-prong outlets "upside down" with the ground lug at the top?
It's supposedly to prevent a short in case something metal falls the
exact right way across a partially plugged in plug. The ground lug
prevents the object from reaching the hot blades. It also means that
your heavy duty plugs have to go in upside down, with the cord coming
out the top instead of the bottom like it should.
Steve
--
/ / /
\ \ \
/ / /
Jim Donohue
cited the proper ABYC spec. and have heard nothing further from you on the
subject so I guess I must presume your original post was simply incorrect.
Jim
Lew Hodgett <lewho...@earthlink.net> wrote in message
news:393C128...@earthlink.net...
> Steven Kennedy wrote:
>
> <snip>
> > Note here that generators and invertors are treated differently than the
NEC
> > would treat them also. However such conditions do not exist on land.
> <snip>
>
> Really.
>
> Guess all those engine-generator sets complete with emergency stand by
> transfer switches found all over the country don't count.
>
>
Jim Donohue
inflammatory "
like
"Keep supposition, opinion, guesses, vague generalities & politics to
yourself. Give
me engineering facts and we will either find an engineering & mathematically
provable answer or disprove the model submitted. Not a bunch of lip
flapping
and jaw jacking suppositions."
Jeez what piece of work. You must find it difficult to walk as you trip
over your ego.
Marcus and I told you virtually the same thing. I used a short form and he
spelled it out. Apparently you require cookbook steps to understand this
stuff.
Lew spoke to an unrelated point and was likely incorrect.
I will not wait for you to get your foot out of your mouth as I am sure it
spends a lot of time there.
Jim
<sven...@earthlink.net> wrote in message
news:393C157C...@earthlink.net...
sven...@earthlink.net
that is like arguing about how many angles can dance on the head of a
pin. You can argue NEC vs ABYC until your all purple in the face. When
all is said and done, it just doesn't matter at the end of the day.
Neither have an enforcement mechanism for boats like local building code
for land structures. Until that happens they can each say what they
want but it won't change what they build or what you buy on boats. It is
all blue sky over the horizon. We are not going to see long queues of
boat owners lined up to buy retrofit transformers nor are builders going
to make installation of transformers SOP. Home builder won't even
install a couple of dollars of hurricane roof rafter clip unless the
local building code holds a gun to there head. And you think boat
builder are any different?
It doesn't mean I agree with it or like it. It is just the way it
is. Lets get over it and move on and making the best out of a bad
situation. There simply is no elegant solution short of a properly
installed transformer to reconcile the needs of a boat underway vs
connected to shore power in port. Add 120 volt generation sources
aboard (gen/inv) and it gets even more difficult to reconcile.
Large scale retrofitting just isn't in the cards. People like
myself that have a 44 ft vessel and know in my own mind why it makes
sense will do it, will. Some folks in the 35-40 ft range may do it.
Much below 35 ft, forget it. The bottom line here is that transformers
will most often turn up on vessels that travel internationally. That is
primarily why we are adding one. To cope with foreign voltages.
Back in the real world your boat comes with an AC safety (green)
that is shorted to AC neutral (white) only on the dock. A separate DC
ground that is deliberately shorted to AC safety (green) at only one
point aboard. When the system is connected to shore power the AC safety
green also has a second unavoidable shorted through earth and your
underwater metal to DC ground. That is what we have to work with. Let
us focus on that.
Marcus G Bell wrote:
> > Steven Kennedy wrote: <snip>
> > > Note here that generators and invertors are treated
> > > differently than the NEC would treat them also. However such
> > > conditions do not exist on land.
> > <snip>
>
> Lew Hodgett (lewho...@earthlink.net) wrote:
> > Really. Guess all those engine-generator sets complete with
> > emergency stand by transfer switches found all over the country
> > don't count.
>
> OK, then I'll ask.
>
> How are all those engine-generator sets complete with emergency
> stand by transfer switches found all over the country treated by
> the NEC differently from the way ABYC treats the analogous system
> in a boat? How are all those engine-generator sets complete with
> emergency stand by transfer switches found all over the country
> treated by the NEC the same as the way ABYC treats the analogous
> system in a boat?
>
Marcus G Bell
> > How are all those engine-generator sets complete with
> > emergency stand by transfer switches found all over the
> > country treated by the NEC differently from the way ABYC
sven...@earthlink.net wrote:
> Gang, gang please. We are getting lost in the minutia of
> something that is like arguing about how many angles can dance
> on the head of a pin. You can argue NEC vs ABYC until your all
> purple in the face. When all is said and done, it just doesn't
> matter at the end of the day.
Sven, if it's all right with you, I'd still like to have my
question answered. It matters to me, it can probably be answered
in a few short paragraphs, and I don't consider it to be
minutiae.
-- Marcus.
Steven Kennedy
Marcus et al, apparently you do not understand that the NEC regards boats as
appliances similar to toasters. Nothing more about the internal wiring of
boats interests them. I regard this as rather like the local regional Bay
Conservation and Control District which regards boats as "bay fill".
However....them's the facts. And your rude pompousness and ever deeper load
of BS (boat shit?) will not make you correct. Quote the NEC or ABYC or get
off the pot.
Do it any way you like on your boat. Just keep your ignorant opinions to
yourself; and stay out of my marina. You must know that some people come
here (this NG) expecting to find actual intelligent discussion and
reasonable, supportable solutions to these very cut and dried questions. If
you know better...go do it. I'm guessing you don't.
skennedy
Jim Donohue <jim_d...@computer.org> wrote in message
news:sjo8qae...@corp.supernews.com...
Jim Donohue
know any way to cite that which does not exist. There ain't no prohibition
against switching neutral if it is done with the other conductors - which is
what ABYC does. I can find no other conflict between ABYC and NEC - with
respect to grounds or grounded neutrals or anything similar. Now cite the
conflicting provisions or admit you over reached.
Truth time.
Jim
Lew Hodgett <lewho...@earthlink.net> wrote in message
news:393C6F0F...@earthlink.net...
> Jim Donohue wrote:
> >
> > Naw - Don't think so. May be a semantics problem. The white wire on a
boat
> > is referred to as the grounded neutral. ABYC E8 8.5.2.1 says
> >
> > "The shore power neutral is grounded through the shore power cable and
shall
> > not be grounded on the boat. "
> >
> > The next clause requires grounding the neutral of an isolation
transformer
> > secondary - a very strange piece of unsafety engineering but the basic
> > grounded ac line is never grounded on the boat.
> >
> > All ABYC sample hooks up in Appendix A also maintain this seperation.
Note
> > also that the grounded neutral is always switched in single phase
hookups.
> >
> > The green safety wire is grounded on the boat - just as it may be at
many
> > points in the house.
> >
> > I see no conflict between this and the NEC. I do not think there would
be
> > very many marinas operating is it were true - at least not with shore
power.
>
> Much of what I have seen in the ABYC specs, including having a
> switching pole in the neutral, as well as establishing multiple ground
> paths, both of which are in violation with provisions of the NEC,
> leads me to belive that whatever they are smoking, they should
> consider going into a different business. They would make a fortune
> selling the stuff.
>
> Again, I will repeat.
>
> If your vessel is plugged into shore power that is provided by the
> utility grid, you must comply with all provisions of NEC.
>
> There are simply no exceptions.
>
> I will grant you that trying to interpret and understand all the
> provisions of the NEC can be a real PITA. especially with all the
> cross referencing that is required.
>
> In another post, some one stated that the distribution panel on a boat
> is really a sub-distribution panel as defined by NEC.
>
> That is precisely the situation when a boat with a distribution panel
> is plugged into the shore power with out an isolation transformer,
> therefore, again all the provisions of the NEC apply.
>
> It is not an easy subject to get your arms around; however, provisions
> of the NEC, for all the documentation problems involved trying to
> correctly understand them, do work, and they do save lives.
>
> If you don't have a code book handy, check your local library. You
> will probably spend the better part of a day trying to get a handle on
> service entrance panels and sub panels.
>
> The subject of emergency transfer panels is at least another day's
> effort.
Marcus G Bell
> > short form and he spelled it out.
Steven Kennedy (sken...@earthlink.net) wrote:
> Again here I have to agree.
> Marcus et al, apparently you do not understand that the NEC
> regards boats as appliances similar to toasters.
Steven, apparently I DO understand that. I said almost just that,
some time back: "The boat's electrical system is thus treated as
if it's just another subpanel or branch circuit, because that's in
fact what it is." Do we really need to differentiate here between
an appliance "plugged" into a branch circuit vs. one permanently
wired as a branch, or will you concede that I may have understood
your point perhaps well before you made it the first
time?
Furthermore, Jim and I have agreed on almost all points, and you
have made a point of voicing your agreement with him on almost all
points, now including the above which you quoted regarded his
agreement with me. How then should I be addressed *by name* and
subjected to such scorn as:
> ... your rude pompousness and ever deeper load of BS (boat
> shit?) will not make you correct. Quote the NEC or ABYC or get
> off the pot. Do it any way you like on your boat. Just keep your
> ignorant opinions to yourself; and stay out of my marina.
Strong words, Steven. Are you sure I'm worthy of them?
> You must know that some people come here (this NG) expecting to
> find actual intelligent discussion and reasonable, supportable
> solutions to these very cut and dried questions. If you know
> better...go do it. I'm guessing you don't.
I believe that I have been engaging in actual intelligent
discussion on this matter. I will give you the benefit of the
doubt in guessing that you have me confused with somebody
else.
Lew Hodgett
>
> Lew - Are you now agreeing that the NEC and ABYC are not in conflict ? I
> cited the proper ABYC spec.
Absolutely not. Just haven't had time to respond to the other post
yet.
Lew Hodgett
Again, I will repeat.
HTH
Lew Hodgett
<snip>
> Firstly..as to Lews abusive post.
<snip>
An interesting choice of words. Didn't realize that stating factual
information was considered abusive. Abusive? Are you sure?
> Proves my point precisely. He knows
> everything because he knows the NEC.
Not sure what the point is, but you give me far too much credit.
> Although I've spent over 20 years w/
> it he knows.
If you say so, I will accept.
>So fine, but the NEC coinsiders your boat an appliance, just
> like the electric skillet he posted. As long as the boat deos not provide:
> a short, an overload or a ground fault...then the NEC doesn't care what it
> is.
Not quite.
Yes, the boat should be considered and treated as if it were an
appliance.
No, the NEC gets very involved if your "appliance" threatens the
integrity of the system. The "appliance" is always considered
expendable.
So what? What does it mean?
What it really means is that the earth ground point established at the
service entrance point is the only permissible ground if you want to
truly protect your "appliance", boat.
> The ABYC itself is not pure, perfect or complete.
Agreed.
> It is however what we
> have to keep people who believe they know everything from harming temselves
> or their "appliances".
A little food for thought.
If an electrical accident occurs on your boat that is plugged into
shore power, you best hope your vessel is in compliance with NEC,
because it is the only chance you have in a court of law.
Since most likely you will be defending yourself in at least a civil
suit, if you are not in compliance with NEC, you best have VERY DEEP
pockets, because your rear end is grass and the plaintiff's attorney
will have the lawn mower.
The plaintiff will have you stone cold at the end of the day.
Marcus G Bell
> Yes, the boat should be considered and treated as if it were an
> appliance. No, the NEC gets very involved if your "appliance"
> threatens the integrity of the system. The "appliance" is always
> considered expendable. So what? What does it mean? What it
> really means is that the earth ground point established at the
> service entrance point is the only permissible ground if you
> want to truly protect your "appliance", boat.
Lew, the installation manuals for my washer and dryer directed me
to establish connection between the appliance chassis and a
rigorous earth ground, preferrably to a metal cold water pipe in
mechanical and electrical contact with the city's water supply.
These are both 120V, "3-prong plug-in" appliances by the way; the
dryer heat is gas-fired. Hardware was included with each appliance
to establish this earth ground: clamp-on terminal for the pipe,
green 16 gauge stranded wire for the run from the chassis to the
earth connection. So these appliances may have 2 "grounds": the
3rd prong, and the green wire chassis connection to earth. I think
I was curious and tested the continuity between the chassis and
the 3rd prong before I hooked everything up...
How does this square with NEC and local codes with which you are
familiar? Is the appliance manufacturer in violation of NEC?
I think we're all agreed that both NEC and ABYC specify that
"neutral" is to be connected to "ground" only at the service
entrance, which would be shoreside if there is no isolation
transformer. Is there perhaps some fuzzy area with the meanings of
"grounded conductor" (that having the property of being grounded
BY another somewhere) and "grounding conductor" (that having the
property of confering ground status TO another here and now)? What
does the NEC say about appliances that have metal casings
connected to the 3rd prong, when said metal casings are expected
to come into physical contact with earth? If we put this appliance
in a black box, can we tell if it's a water pump, a washing
machine, or a boat? If the rules are different for each of these
scenarios, then it would be interesting to understand the
reasoning behind the differences.
Lew Hodgett
> Lew, the installation manuals for my washer and dryer directed me
> to establish connection between the appliance chassis and a
> rigorous earth ground, preferrably to a metal cold water pipe in
> mechanical and electrical contact with the city's water supply.
> These are both 120V, "3-prong plug-in" appliances by the way; the
> dryer heat is gas-fired. Hardware was included with each appliance
> to establish this earth ground: clamp-on terminal for the pipe,
> green 16 gauge stranded wire for the run from the chassis to the
> earth connection. So these appliances may have 2 "grounds": the
> 3rd prong, and the green wire chassis connection to earth. I think
> I was curious and tested the continuity between the chassis and
> the 3rd prong before I hooked everything up...
>
> How does this square with NEC and local codes with which you are
> familiar? Is the appliance manufacturer in violation of NEC?
The water pipe in your place of residence and the earth ground rod for
the service entrance panel serving that same residence are probably
less than 100 feet from each other. The relative electrical potential
between two points that close together would be practically non
existent. (See below for ground currents).
> I think we're all agreed that both NEC and ABYC specify that
> "neutral" is to be connected to "ground" only at the service
> entrance, which would be shoreside if there is no isolation
> transformer.
I certainly hope so.
>Is there perhaps some fuzzy area with the meanings of
> "grounded conductor" (that having the property of being grounded
> BY another somewhere) and "grounding conductor" (that having the
> property of confering ground status TO another here and now)?
Where human beings are involved, things can always get "fuzzy". It's
the nature of the beast.<G>
>What
> does the NEC say about appliances that have metal casings
> connected to the 3rd prong, when said metal casings are expected
> to come into physical contact with earth? If we put this appliance
> in a black box, can we tell if it's a water pump, a washing
> machine, or a boat? If the rules are different for each of these
> scenarios, then it would be interesting to understand the
> reasoning behind the differences.
Without going to a current code book and doing so further research,
can't give you a specific answer to this specific question.
No question the subject is addressed and covered, I simply can't quote
book chapter and verse from memory.
Most of the examples you cite, would typically be found in a residence
where any contact with the earth, a basement floor for instance, would
again be within a few feet of the earth ground rod. (See below for
ground currents).
Even if they are not, such as a well pump on a farm located several
hundred feet from the service entrance panel, it would not be a
problem.
WHY?
The earth ground would be maintained, and people would be safe;
however, probably have minute currents flowing in the ground because
of the possible difference in potential between the pump ground and
the service entrance ground.
There are lots of the stray currents (ground currents) flowing in the
earth and are of concern only to those involved in the cathodic
protection industry.
As an aside, ever see the gas company installing graphite anodes to
the underground natural pipe lines running down the street for
cathodic protection?
A boat; however, represents a special consideration because it is
normally in the water. Often that water is the same water used by
people to swim in.
Having those same stray ground currents flowing in the water as a
result of improper grounding, can be a BIG problem for not only people
trying to swim, but also because of the cathodic protection problems
it creates.
Using only the earth ground at the shore power service entrance makes
this problem go away.
HTH
Steven Kennedy
here, NO boats ANYWHERE that are completely NEC! Yours included. I'm
absolutely certain that I could find dozens of deficiencies on ANY boat over
12' long. IM(less than)HO the only way to make a boat meet NEC would be to
strip it of all electrical everything. The NEC now has stuck it's
regulatory nose farther into now voltage than ever. We should I suppose all
be like Lynn & Larry Pardey with no engine or technical anything. Who needs
a winch???? It might not surprise you to hear that Lynn & Larry are known
worldwide as Lynn & Larry TOW ME. I wouldn't want to do without what few
modern conveniences one has on a small boat out on a big sea. I'll stand
behind ABYC and NEC on this issue.
I feel the need to keep reminding you that the NEC is not interested in you
having your boat meet their standards. It can't and won't and no amount of
threats on your part will make it so.
As for the discussion of "switching neutrals". Unless I missed part of your
rant...you guys are missing point. ABYC is primarily (pardon the pun)
speaking again about accidental (idiot) reversal of polarity. They are
referring to Mains Circuit Protection, not simple load "switching".
SKENNEDY
Lew Hodgett <lewho...@earthlink.net> wrote in message
news:393C7473...@earthlink.net...
> Steven Kennedy wrote:
>
> <snip>
> > Firstly..as to Lews abusive post.
> <snip>
>
> An interesting choice of words. Didn't realize that stating factual
> information was considered abusive. Abusive? Are you sure?
DEPENDS LARGELY UPON ITS ACCURACY AND ITS INTENT.
>
> > Proves my point precisely. He THINKS HE knows
> > everything because he knows the NEC.
>
> Not sure what the point is, but you give me far too much credit.
UNINTENDED
>
> > Although I've spent over 20 years w/
>
> If you say so, I will accept.
GOSH THANKS. NICE TO KNOW YOU'LL VALIDATE MY EXISTENCE.
>
> >So fine, but the NEC coinsiders your boat an appliance, just
> > like the electric skillet he posted. As long as the boat deos not
provide:
> > a short, an overload or a ground fault...then the NEC doesn't care what
it
> > is.
ABSOLUTELY. THIS IS, LEW, NOT AN OPINION BUT LEGAL FACT.
> No, the NEC gets very involved if your "appliance" threatens the
> integrity of the system. The "appliance" is always considered
> expendable.
>
> So what? What does it mean?
WHAT IT MEANS, LEW, IS THAT UNLESS THE FAULTS I STATED ABOVE EXIST; THE NEC
WOULD NOT APPLY. PERIOD.
> > The ABYC itself is not pure, perfect or complete.
>
> Agreed.
I'M SURE THEY'RE ARE THRILLED TO HEAR IT.
>
Most of us are comfortable with what we know and less so with what we do not
know. I think it's great you know the NEC. Let's point out however that
less than none(?) of it applies anywhere else on this planet other than the
bitty country we've chosen.
Besides, its intent is to cover construction (and temp.) medium and high
voltage service, wiring, lighting etc. It specifically chooses NOT to cover
other areas. No such thing as a NEC approved toaster.
Get a grip. These guys are not gods. This, our (floating) field is
intentionally and largely ignored by the NEC.
Have you been in the service, or work for the fed. government? You'll find
that most of the military and some of the federal government ignore the NEC
and for that matter UL where it suits them to do so. Then on the other
hand, they cannot be sued.