That was the Royal Navy's choice when they specified Fintry thirty
years ago and we will continue this with her new electrical system.
The only electrical connections to the hull will be green safety
ground and radio ground for the SSB (which is isolated from electrical
ground).

We will have ground fault alarms on both the DC and the AC systems so
that if either gets shorted to the hull we'll know about it early.
Shore power will come aboard through isolation transformers.

Jim Woodward
www.mvFintry.com



(Lee Huddleston) wrote in message . ..
On Thu, 4 Sep 2003 17:18:03 +0100, "Joao Penha-Lopes"
wrote:

Hello everybody,
I have just upgraded from a GRP 30ft sloop to a steel hull 40ft sloop.
Everything is in excellent state except for the electrical wiring which will
certainly consume most of my winter weekends....

My main worry before everything else is to plan for electrical grounding and
I have read the most opposite opinions.

Can somebody share his experience with me, please ?

Cheers
Joao

Joao,

I have a 43 foot steel hull and deck sailboat. I make sure that all
electrical wiring and connections are kept away from the hull and
deck. I do not ground to the hull and highly recommend that you not
ground there either. I even try to keep the engine as disconnected
electrically from the hull as possible. For example, the alternator
and the starter have their own negative cables back to the battery
bank rather than using the engine block as the negative.

I recommend the Nigel Calder book, Boatowner's Mechanical And
Electrical Handbook (or Manual).

I feel that connecting anything electrical to your steel hull is
asking for serious trouble. One mistake and you could completely
destroy your hull.

Lee Huddleston
s/v Truelove

On 10 Oct 2003 07:54:37 -0700, (Jim Woodward)
wrote:

That was the Royal Navy's choice when they specified Fintry thirty
years ago and we will continue this with her new electrical system.
The only electrical connections to the hull will be green safety
ground and radio ground for the SSB (which is isolated from electrical
ground).

We will have ground fault alarms on both the DC and the AC systems so
that if either gets shorted to the hull we'll know about it early.
Shore power will come aboard through isolation transformers.

Jim Woodward

Jim,

Would you have a recommendation for an isolation transformer? The
only one that I have found so far ate up a lot of the power before it
could get into the boat. That seemed strange to me, but maybe I was
reading the specs incorrectly. Also the price seemed to be very high.
Of course, protecting my beloved boat from galvanic corrosion is
probably worth a lot if that is what is necessary.

By the way, you mentioned DC and AC ground fault alarms. Who makes
them and are they available to private individuals?

Thanks in advance for your help.

Lee

Lee:

Yes, they are pricey, heavy, and hot. Transformers are typically
around 95% efficient, so pay attention to heat generation -- they do
get hot.

I found a bunch of Topaz 5kw ultra isolation transformers when we were
outfitting Swee****er in 1995 and bought them at US$100. I still have
two. Surplus sales of Nebraska has them new for $1395:
http://www.surplusales.com/Transform...tionXmers.html

However, the good news is that any transformer is an isolation
transformer for our purposes -- it won't do quite as good a job on
keeping out unwanted frequencies, but we're primarily interested in
1) keeping out DC and
2)establishing an ungrounded AC system.
So take a look at things like
https://www.surpluscenter.com/item.a...tname=electric

It will do 5KW. You can put in 240 and take out 120/240 three wire
just like your house, or put in 120 and take out 120.
(240x480 means you can put in either 240 or 480)
(120/240 means you can take out 120, 240, or both)
(You do 120120 by hooking it up like 240240)

BTW, you do not want an autotransformer -- which will change voltage
but does not isolate.

If you feel more comfortable with a "real" isolation transformer, I
ran into a guy at the Maine BoatBuilders' show that was having them
made.
WesTran Power
5160 NW Five Oaks Drive
Hillsboro, OR 97124

(no web site)

He was selling a "marine grade" (whatever that means) 6KW unit with
pretty good specs for $900.

As far as ground fault alarms go, the typical big ship installation is
a light in series with a push button wired from one of the hot wires
to the hull, and then the same thing on the other hot wire. The two
push buttons are on the same actuator (a dpst). The bulbs are
typically rated for the system voltage, so when you push the buttons,
both come on at half voltage. If there's a fault on either side, that
light is shorted out and stays dark, while the other light is getting
full voltage, so it's brighter than usual.

Like this (sometimes ASCII graphics actually work, maybe):

hot1---pb---light---hull---light---pb---hot2

(with the two pb on one frame).

Jim Woodward
www.mvFintry.com





(Lee Huddleston) wrote in message . ..
On 10 Oct 2003 07:54:37 -0700, (Jim Woodward)
wrote:

That was the Royal Navy's choice when they specified Fintry thirty
years ago and we will continue this with her new electrical system.
The only electrical connections to the hull will be green safety
ground and radio ground for the SSB (which is isolated from electrical
ground).

We will have ground fault alarms on both the DC and the AC systems so
that if either gets shorted to the hull we'll know about it early.
Shore power will come aboard through isolation transformers.

Jim Woodward

Jim,

Would you have a recommendation for an isolation transformer? The
only one that I have found so far ate up a lot of the power before it
could get into the boat. That seemed strange to me, but maybe I was
reading the specs incorrectly. Also the price seemed to be very high.
Of course, protecting my beloved boat from galvanic corrosion is
probably worth a lot if that is what is necessary.

By the way, you mentioned DC and AC ground fault alarms. Who makes
them and are they available to private individuals?

Thanks in advance for your help.

Lee

Jim Woodward wrote:
Lee:
snip
However, the good news is that any transformer is an isolation
transformer for our purposes --
snip

This is not correct. An autotransformer has a single winding and does
not provide isolation.
Jim

I think I said that, two paragraphs further along. I guess I assume
that on a post with a lot of techincal content, that the reader will
wade through the whole thing before going out and spending money.

Jim


Jim wrote in message ...
Jim Woodward wrote:
Lee:
snip
However, the good news is that any transformer is an isolation
transformer for our purposes --
snip

This is not correct. An autotransformer has a single winding and does
not provide isolation.
Jim

Jim,

Thanks for all the information, leads, and offers. At this point, I
do not have enough knowledge to make any kind of informed choice
regarding an isolation transformer. Can you direct me to a source
where I can read and learn more of what I need to know?

Lee Huddleston

First the usual CYA stuff -- electricity can be dangerous in a whole
variety of ways. If you don't understand it, hire an expert. There's
a lot of good information available on the web, including here, but
good electrical practice finally comes down to details that you need
to do because you've learned, somewhere, to do them right. And BTW, a
boat is not a house, so a license to do wiring ashore says nothing
about a person's skills in wiring boats.

With that said, an isolation transformer is a pretty simple device --
two wires in and two wires out -- although there are often a lot more
leads than two, as they can usually be connected for different or
multiple voltages. Figuring out the leads is like figuring out how to
wire a 120/240VAC motor -- it's just cookbook and often there's a
diagram. If not, we have ways....

I usually refer people to Nigel Calder's Boatowner's Mechanical and
Electrical Manual for all mechanical and electrical stuff -- in this
case there's a diagram and a couple of paragraphs.

This is not a bad little piece on the subject:
http://www.smpstech.com/qa/qa0002.htm

This has more than any ordinary mortal needs to know, but a number of
details can be picked out if you're strong enough to ingnore the heavy
math.
http://www.du.edu/~jcalvert/tech/transfor.htm

Aside from actually connecting the thing, the only other issue is
sizing. Generally, if you plug into a standard 30A 120V shore outlet,
you'll want a 3.6kw transformer (30x120 ~=~ 3.6kw). Larger won't hurt
(other than being heavier) within broad limits. Smaller is OK, too,
provided you put a circuit breaker on the shore side of the
transformer that is the same rating as the transformer. Of course,
smaller means you can't run as much stuff....

If you have a larger boat and regularly use 240VAC, then you can run
50A 240 from standard marina outlets, but this takes a 12kw
transformer, which is starting to get heavy and pricey.

Don't forget, it's got to mounted somewhere that can stand a big
weight, is dry, and won't get too hot with a couple of hundred watts
being thrown off. It may hum a little, so you won't want it as a
pillow.

Jim Woodward
www.mvFintry.com

(Lee Huddleston) wrote in message . ..
Jim,

Thanks for all the information, leads, and offers. At this point, I
do not have enough knowledge to make any kind of informed choice
regarding an isolation transformer. Can you direct me to a source
where I can read and learn more of what I need to know?

Lee Huddleston

I usually refer people to Nigel Calder's Boatowner's Mechanical and
Electrical Manual for all mechanical and electrical stuff -- in this
case there's a diagram and a couple of paragraphs.

I have the Nigel Calder book and have almost committed it to memory.
That is what caused me to want an isolation transformer in the first
place.

This is not a bad little piece on the subject:
http://www.smpstech.com/qa/qa0002.htm

Yes, it does give some good information.

This has more than any ordinary mortal needs to know, but a number of
details can be picked out if you're strong enough to ingnore the heavy
math.
http://www.du.edu/~jcalvert/tech/transfor.htm

Wow! "Ask and ye shall receive." Thanks. I will reread this
material until I think that I understand most of it. If I can do
that, I doubt that there will be much about transformers that I will
not know.

Aside from actually connecting the thing, the only other issue is
sizing. Generally, if you plug into a standard 30A 120V shore outlet,
you'll want a 3.6kw transformer (30x120 ~=~ 3.6kw).

The smallest isolation transformer made by Charles Industries,
recommended in the next post, just happens to be their 3.6kw
transformer. Looks like a good lead.

Thank you very much for all your help.

Lee Huddleston
s/v Truelove

AFAIK, there is only one that meets the ABYC specs, & that is made by
Charles Industries (www.charlesindustries.com). Something about
isolaitng the ground as well as the conductors.

Michael Porter



(Lee Huddleston) wrote:



Jim,

Would you have a recommendation for an isolation transformer? The
only one that I have found so far ate up a lot of the power before it
could get into the boat. That seemed strange to me, but maybe I was
reading the specs incorrectly. Also the price seemed to be very high.
Of course, protecting my beloved boat from galvanic corrosion is
probably worth a lot if that is what is necessary.

By the way, you mentioned DC and AC ground fault alarms. Who makes
them and are they available to private individuals?

Thanks in advance for your help.

Lee

Michael Porter Naval Architect / Boatbuilder
mporter at mp-marine dot com
www.mp-marine.com

AFAIK, there is only one that meets the ABYC specs, & that is made by
Charles Industries (www.charlesindustries.com). Something about
isolaitng the ground as well as the conductors.

Michael Porter


Michael,

Thanks for the lead. The smallest Charles Industries transformer is
just the size that Jim Woodward recommends. Looks like a good
possibility.

BTW, I could not figure out how to find the price on the transformer.
Have I just overlooked it on the web site or will I just need to give
them a call?

Lee Huddleston
s/v Truelove