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

I have seen this grounding questions with metal boats before and I dont
understand what the issue is. If the boat has a motor I can almost guarentee
its grounded somewhere to the hull weather its inboard or outboard. Would
someone actually go through the trouble and expense to isolate the electrical
system from the hull? That would take a lot to do!!

Interesting and difficult subject. I, too, will be interested in
thoughts from others.

When we bought Fintry (see www.mvfintry.com 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 a
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
www.mvfintry.com



"Joao Penha-Lopes" wrote in message ...
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

It's easy enough to check whats grounded to what, and whats not with a
continuity meter. I dont see how you could keep it from grounding with a metal
hull without spending a fortune. Something is going to touch somewhere at
least on the DC side.

CCred68046 wrote:
I have seen this grounding questions with metal boats before and I dont
understand what the issue is. If the boat has a motor I can almost guarentee
its grounded somewhere to the hull weather its inboard or outboard. Would
someone actually go through the trouble and expense to isolate the electrical
system from the hull? That would take a lot to do!!

The debate is long & I'll stay out of it for now, however you are
mistaken Cred about "almost guaranteeing" engine electrics are grounded,
indeed most proper marine engine electrics are not.

True marine electrics even on big diesels where the spark risk is
minimal, have all their electrics above ground. The starters &
alternators etc have their own earth returns kept above the cases, so if
the user/engine manufacturer chooses you can have a completely above
ground system with none of the electrics able to get to the prop shaft
etc via the block.

Diodes leak.


K.

I'll stay out of it for now, however you are
mistaken Cred about "almost guaranteeing" engine electrics are grounded,
indeed most proper marine engine electrics are not.


How can they not be? Every DC and AC motor I know of requires a + and -
current to run. I consider the - to be ground. The outdrive is connected to the
engine which must have a + and - (or ground) to run, and is fastened to the
metal hull. If theres no continuity there you will have to show me with a VOM.

True marine electrics even on big diesels where the spark risk is
minimal, have all their electrics above ground.

Define "above ground". Again, they require a positive and negitive to operate.


The starters &
alternators etc have their own earth returns kept above the cases, so if
the user/engine manufacturer chooses you can have a completely above
ground system with none of the electrics able to get to the prop shaft
etc via the block.

And the block is grounded (or negitive) and is connected metal to metal to the
metal outdrive which is bolted to the metal hull. The connection might not be
the best but it is there and I have to believe its making a pretty decent
connection. I have an aluminum boat with an outboard and there is definately
continuity from the hull to the motor.. It would take some pretty serious
custom made isolators to stop it.
I can admit it when I'm wrong so if someone can show me that I am I would like
to know how they work.

"CCred68046" wrote in message
...
I'll stay out of it for now, however you are
mistaken Cred about "almost guaranteeing" engine electrics are grounded,
indeed most proper marine engine electrics are not.


How can they not be? Every DC and AC motor I know of requires a + and -
current to run. I consider the - to be ground. The outdrive is connected
to the
engine which must have a + and - (or ground) to run, and is fastened to
the
metal hull. If theres no continuity there you will have to show me with a
VOM.

True marine electrics even on big diesels where the spark risk is
minimal, have all their electrics above ground.

Define "above ground". Again, they require a positive and negitive to
operate.


The starters &
alternators etc have their own earth returns kept above the cases, so if
the user/engine manufacturer chooses you can have a completely above
ground system with none of the electrics able to get to the prop shaft
etc via the block.

And the block is grounded (or negitive) and is connected metal to metal to
the
metal outdrive which is bolted to the metal hull. The connection might
not be
the best but it is there and I have to believe its making a pretty decent
connection. I have an aluminum boat with an outboard and there is
definately
continuity from the hull to the motor.. It would take some pretty serious
custom made isolators to stop it.
I can admit it when I'm wrong so if someone can show me that I am I would
like
to know how they work.


There is no requirement for the coil(s) to be grounded to the case. While I
have no experience with a floating ground in a 12 or 24 volt ignitions, all
high voltage motors and generators that I have ever worked with are isolated
from the frame. There is no practical reason that a low voltage system
can't be wired the same way.

The only area where it may be difficult to separate the ground from the
frame is the spark plugs. Even this is not an insurmountable problem; it is
possible to make a spark plug with two electrodes. The only place I have
seen this used in practice is turbine APUs.

Mark Browne

That was my conclusion for the future, but as I said, Fintry was built
in 1972 with no DC grounding and thirty years later had no ground
faults. Of course the Royal Navy maintenance schedules would put us
all to shame....

Jim Woodward
www.mvfintry.com

obull (CCred68046) wrote in message ...
It's easy enough to check whats grounded to what, and whats not with a
continuity meter. I dont see how you could keep it from grounding with a metal
hull without spending a fortune. Something is going to touch somewhere at
least on the DC side.

"CCred68046" wrote in message
...
The only area where it may be difficult to separate the ground from the
frame is the spark plugs. Even this is not an insurmountable problem; it
is
possible to make a spark plug with two electrodes.

I can agree with your post, I understand the high voltage motors and
generators. The spark plug scenerio would require 2 wires to each plug
and the
plugs would have to be insulated from the block and I can say I've ever
seen
that... Is that the way they are? Now I'm real interested

Yes, there are two wires running to the plugs on some turbines.

I spend considerable time lurking in aircraft hangars. You see all sorts of
odd things done on aircraft systems.

The starting spark on a turbine engine has considerably higher power than a
standard gas engine - It has enough oomph that you can hear the snap of the
spark over the whine of the compressor when it starts up. It has to have
"lot 'o zots" to fire kerosene at the high air velocities in a turbine
engine.

Mark Browne

K Smith wrote in message ...
CCred68046 wrote:
I have seen this grounding questions with metal boats before and I dont
understand what the issue is. If the boat has a motor I can almost guarentee
its grounded somewhere to the hull weather its inboard or outboard. Would
someone actually go through the trouble and expense to isolate the electrical
system from the hull? That would take a lot to do!!

The debate is long & I'll stay out of it for now, however you are
mistaken Cred about "almost guaranteeing" engine electrics are grounded,
indeed most proper marine engine electrics are not.

How can an electrical circuit be made if there isn't any ground?