Interesting and difficult subject. I, too, will be interested in
thoughts from others.
When we bought Fintry (see <a style='text-decoration: underline;' href="http://www.mvfintry.com" target="_blank">www.mvfintry.com</a> for background) she had
two electrical systems -- 24VDC and 220VDC. Their negative sides were
common and neither of them was grounded anywhere. There were ground
fault test lights on the main panel.
We will have both 24VDC and 120/240VAC (shore power, gensets,
inverters, the whole nine yards, set up for both 50 and 60Hz shore
power) and grounding is a real question.
Here's where I think I come out:
On the 24VDC side, I'll solidly ground the negative to the hull at one
point. To some extent "one point" is an illusion, because unless you
work very hard at it, there are all sorts of places where there's an
unexpected ground. Some of these are:
Engine starters (can be isolated, most aren't)
Engine instrument senders (same thing)
Alternators (isolated ground are more expensive)
Radios, particularly SSB -- you want the antenna tuner radio frequency
to be grounded to the hull for good performance, but this often brings
a power ground.
The reason I chose this is that it's better than trying to be
absolutely sure that none of the above is grounded and then, for
example, have a fault result in your engine starter trying to take its
ground side through your radio (this should, of course, blow a fuse).
Of course, it goes without saying that you always have two wires going
to everything -- never use the hull as a ground return as an
automobile does. It's also helpful, if possible, to be able to
disconnect the single point ground to make sure that it is, indeed, a
single point.
On the AC side, the most important thing is to use an isolation
transformer on the shore power entrance. These are expensive (US$900
new for 5KW) but absolutely essential, as they ensure that there is no
DC sneaking onto the boat on the AC wires from elsewhere in the
marina. (The neutral and hot shore power connect to one side; the
neutral and hot boat power come out the other -- no DC gets through.)
In US practice, you can use the same transformer to take in 120 or
240, depending on what's available, and always put out 120/240, three
wire plus ground -- this requires a switch on the shore side to change
the winding connections. It can also have multiple taps to adjust low
(or, much more rarely, high) voltages.
Another way to accomplish the same thing, particularly if you're going
back and forth between fifty and sixty hertz areas, is to hook the
shore power to a large universal battery charger and then run the boat
from an inverter. Large boats use devices which combine the two
functions into one and allow you to plug into any power (single or
three phase, any voltage, any frequency), but such things are very
expensive.
I will then connect the neutral and the green ground together on the
boat side of the transformer and connect them to the single point
ground. This is contrary to big ship practice, which usually lets
both side of the AC power float, but is consistent with yacht practice
in the USA. Big ship practice is to have two ground fault lamps, one
from each hot wire to ground. These have the effect of making sure
that the hull is electrically halfway between the two hots, as long as
the lamps aren't burned out. If a lamp goes out, there's either a
ground fault on that side or a burned out lamp.
In the US, the neutral is the center, electrically halfway between two
hot wires, which, when used together give 240VAC and when either is
used with the neutral, give 120VAC. European practice is to use one
side of the 230VAC as the neutral. When 115VAC is used in England,
and maybe in Europe, I don't know, it's taken from a transformer
running off the 230.
As part of the system, I will have a sensitive ammeter (both AC and
DC) in the ground wire to the hull to monitor whether there is current
flowing there -- shouldn't ever be any.
Then, I'll keep a close eye on all the zincs and say my prayers.....
Jim Woodward
<a style='text-decoration: underline;' href="http://www.mvfintry.com" target="_blank">www.mvfintry.com</a>
"Joao Penha-Lopes" <jpl DeleteThis @rgps.pt> wrote in message news:<3f577352$0$2244$a729d347@news.telepac.pt>...
> 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<!-- ~MESSAGE_AFTER~ -->
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