Electric Grounding - steel hull
 

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

Electric Grounding - steel hull
 

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!!

Electric Grounding - steel hull
 

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

Electric Grounding - steel hull
 

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.

Electric Grounding - steel hull
 

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.

Electric Grounding - steel hull
 

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.

Electric Grounding - steel hull
 

"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

Electric Grounding - steel hull
 

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.

Electric Grounding - steel hull
 

"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

Electric Grounding - steel hull
 

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?

Electric Grounding - steel hull
 

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

Thanks for sharing that, I didnt realize turbines were that way. They must have
a huge magneto if you can hear em snap :)
I have a good friend who is an aircraft mechanic USAF and he told me that on
piston engine aircraft many will have 2 wires per plug but the reason is for
redundancy (in case one fails), they are both hot.

Electric Grounding - steel hull
 

"CCred68046" wrote in message
...
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

Thanks for sharing that, I didnt realize turbines were that way. They must
have
a huge magneto if you can hear em snap :)
I have a good friend who is an aircraft mechanic USAF and he told me that
on
piston engine aircraft many will have 2 wires per plug but the reason is
for
redundancy (in case one fails), they are both hot.

You are correct on the light aircraft ignition.

I am interested in the DIY turbine engine hobby so I ask a lot of questions
when I lurk in aircraft technical offices. Some of the old timers have some
interesting things laying around for show and tell.

One of the more curious approaches to generating the high energy required by
turbine engines was the "opposite-polarity system." In this circuit two
electrodes extended into the combustion chamber. Each electrode becomes
alternately charged with positive and negative potential. This allows double
the voltage across the electrode without the corresponding need for higher
voltage insulation in the power leads.

Modern capacitor discharge igniters have made these exotic systems
unnecessary; most modern turbines use an annular ring, single gap igniter.
Some of the exciters on these thing pumps out in excess of 20 Jules
discharges! I have not seen one that uses a magneto, the power source is
either 24v DC or 115/400hz AC so they have a lot of power to play with. The
firing rate is pretty slow, it sounds like about four zaps a second, so they
can build up this monster spark. These ignitions have big bold warning
about the lethal nature of the spark, and after seeing the spark these
things throw, I believe it! As far as redundancy goes, the engines I have
seen use completely separate dual exciters, power leads, and igniters.

Mark Browne

Electric Grounding - steel hull
 

"basskisser" wrote in message
m...
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?

It has one - It just does not use the engine or drive components to provide
the current return path; a separate "ground" wire carries the juice back.
Look up "ground loops" on google. This type of wiring allows effective
assaults on this nasty problem. If you are trying to eliminate radio
interference problems or reduce electrically induced corrosion problems,
this can make a lot of sense.

There have been a few times that I wished that automotive components were
built this way.

Mark Browne

Electric Grounding - steel hull
 

Jim,

Thanks for an excellent and thoughtful post.

I frequently work with systems that have multiple nested grounding system.
We try to reconcile the competing interests of UL safety requirements, FM
intrinsically safety requirements, analog measuring circuits trying to
resolve 0.1 microvolt out of 10 millivolts riding on a 2.5 v differential
load cell output (multiple summed load cells in the system), and the onboard
communication radio to carry the measurements to a central processing
system. Sometimes these systems are installed on electrically powered
material moving equipments so we have to contend with high drive currents
coming off the same battery where we get our power. These drive systems
typically have their own stringent grounding rules to keep the motor
controller alive. To top it all off, in high humidity environments, low
level contaminants add additional and unintended current paths. We have
developed a set of rules and methodology that works, but it is hard to
explain why we do some of the things we do without getting into a lot of
seemingly useless minutia.

I did a miserable job of relating a sub-set of the rules we have to follow
into the boating environment; you provided a much more useful description.

Mark Browne


"Jim Woodward" wrote in message
om...
Mark:

I don't like to be nit picking about teminology, but a lot of
electrical confusion can be avoided if we're consistent.

You don't need any ground in an electrical circuit. A plastic
flashlight is a simple example of something that doesn't have a
ground. The doorbell in your house is ungrounded even if supplied by
a transformer, the transformer isolates the doorbell wiring from the
ground. And so forth.

A "ground", or in British usage, an "earth", is just that, literally a
connection to the earth, which is a pretty good conductor because
there's lots of it.

So, strictly speaking, there isn't a ground unless there's a
connection to terra firma or the sea.

However, in many pieces of equipment -- autos and radios come to mind
as good examples -- one side of the power supply is attached to the
chassis. In auto and radio practice the chassis is used as the return
for all the current on that side (usually negative now, but positive
ground used to be common). Strictly speaking this is a "chassis
ground", not a "ground", but nobody's that strict.

On boats, there is usually a single point connection from ground to
the negative side of the DC supply and -- only when the supply is on
board, NOT with shore power -- the neutral side of the AC supply
(white wire in US practice). All current is through two wires, never
through the hull, mast, or anything else.

In the case of boats, many large vessels have ungrounded ("floating"
is the term of art) electrical systems. The engine starters, gauge
sensors, and alternators all have two wires going to them, both of
which are insulated from their metal bodies. Everything else is also
insulated and there are alarms to indicate ground faults -- a fault
connection from one side of a power supply to the hull. This is true
of both their DC systems and their AC, house supply, systems.

We're so used to engine starters being grounded on one side that we
forget that almost all electric motors except starters are insulated
from their metal cases -- insulated motors are the rule and automotive
starters are very much the exception.

(Now a little technical stuff) The reason that large vessels having
floating electrical systems is that it is easy to detect ground faults
when the system is floating. Ground faults are bad because, aside
from obvious safety issues, current will be conducted through the hull
leading to possible electro-chemical erosion. With a grounded system,
ground faults on the hot side are easy to detect -- a circuit breaker
blows. Ground faults on the other, neutral, side are very subtle and
hard to detect. You can detect them by careful measurements, but in a
marine environment careful measurements are almost impossible because
there's always a little leakage caused by moist salt air. So they just
sit there, conducting current, and damging the hull.

Jim Woodward
www.mvfintry.com

"Mark Browne" wrote in message
. net...
"basskisser" wrote in message
m...
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?

It has one - It just does not use the engine or drive components to
provide
the current return path; a separate "ground" wire carries the juice
back.
Look up "ground loops" on google. This type of wiring allows effective
assaults on this nasty problem. If you are trying to eliminate radio
interference problems or reduce electrically induced corrosion problems,
this can make a lot of sense.

There have been a few times that I wished that automotive components
were
built this way.

Mark Browne

Electric Grounding - steel hull
 

basskisser wrote:
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?

It's as expected, by a second wire going back to earth.

Say alternators there is only two connections to the alternator case &
therefore the engine block itself?? The fields are usually controlled by
the regulator earthing them back to the negative side of the battery via
the case/block & earth strap, insulate the second slip ring bush from
the case (the same as one is already) & include an extra light earth
wire so now the fields are still "earthed" to the battery but you've cut
the case/block etc out of the circuit & obviously you no longer have an
earth strap from the battery to the block.

Likewise the starter, it's only convenience that they don't require two
wires,& again it's only because one set of starter motor brushes are
earthed to the starter case that current can get to the block, insulate
then as the delivery set of brushes already are & then the case is above
ground. You then need an earth strap direct to a terminal on the starter
instead of the engine block.

Most larger proper marine diesels have all their electrics above ground
with specific earths included in their wiring. Given spark engines are
not really "proper" :-) marine engines, we're unaware of any that have
such a system.

The biggest problem is leaking currents to the block & hence the
stainless prop shaft with a bronze prop attached, bad enough but add a
steel hull & .........



K

Electric Grounding - steel hull
 

Thanks, Mark:

I think I have a good theoretical understanding of the issues. I have
some practical experience with electric systems on boats connected to
various shore systems around the world. You obviously have far more
practical experience.

So, I ask, what would you do with Fintry's grounds? Nothing from the
shore comes past the isloation transformers. Clearly the green wire is
grounded to the hull, no question there. On the DC side do we float
or ground the negatives? On the AC side, do we ground the neutral
(the center of the 240, as in common US single phase practice)?

Of course, when I say "ground", I mean at a single point, in so far as
it is possible. This would include insulating steel appliances from
the steel deck and taking other precautions against ground loops.

Issues:
On the DC side, I think I have everything isolated. It may be that
the engine starting circuits will be grounded negative, but the 24VDC
house loads can all be isolated.

Radios are always a question. I think the antenna ground on the SSB
is isolated from the negative power supply, but I'm not sure. If not,
the 12VDC system negative may have to be grounded to the hull, because
we certainly want the antenna counterpoise grounded (or can it be
capacitively coupled?)

On the AC side, I look at big ship practice and think that it makes a
lot of sense. Then I read of the dangers of floating systems and I
come back to earth, so to speak....

What would you do?




Details:

79', 150 ton steel hull and deckhouse, aluminum wheelhouse.

Five diesel prime movers:
New Cat 3406 main
Perkins 6-354 for hydraulics, pumps, alternator (old genset engine)
Two new Northern Lights 9kw 120/240VAC 60Hz 1ph gensets
Hatz single cylinder, rope start, for fire and bilge pump.

Four DC systems:

Engine starting -- one 24DC bank, isolated from everything else -- all
four engine alternators charge it while running. (Lest anyone worry
about single point failures, the 6-354 auxiliary has a spring
starter).

24VDC house system -- one big battery bank, charged by the Cat and the
Perkins (2x125A 24VDC Electrodyne brushless alternators on each
engine), as well as 240VDC universal chargers (paired for redundancy).
This system is mostly for boat operation -- electronics, nav lights.
This also drives two big inverters to power 120/240VAC house loads
while underway.

24VDC emergency system -- battery bank on upper deck, for spare nav
lights, electronics, emergency lights in the event of a main system
failure (fire in the engine room, etc.) Charged by battery charger and
by a diode off house system.

12VDC for radios -- You can't buy a VHF or SSB (except commercial
units at 4x prices) that runs off 24VDC, so we have to do both. I
love 24VDC, but hate the fact that as a practical matter, it means you
have to have both 12 and 24. Batteries on the upper deck (they're also
needed in emergency), charged by 240VAC charger. I chose this way,
because a 30A 24VDC-12VDC converter and spare for the SSB would be
more money and the 12VDC battery capacity would have to be there for
emergency use anyway.

120/240 VAC 1phase for hotel loads, major auxiliaries (pumps, air con,
etc.).

Isolation transformers on shore power. Whether shore power is 120 or
240, we'll use the transformers to create the usual US system --
hot-neutral-hot, 120/240.

In 50hz places we'll use 50hz wherever we can (lighting and air con,
for example) and supply 60hz from a universal battery charger taking
in 230VAC 50hz going to 24VDC back to 120/240 60hz. Except for bussing
both 50 and 60hz, the AC side is pretty conventional.



Jim Woodward
www.mvfintry.com



"Mark Browne" wrote in message . net...
Jim,

Thanks for an excellent and thoughtful post.

I frequently work with systems that have multiple nested grounding system.
We try to reconcile the competing interests of UL safety requirements, FM
intrinsically safety requirements, analog measuring circuits trying to
resolve 0.1 microvolt out of 10 millivolts riding on a 2.5 v differential
load cell output (multiple summed load cells in the system), and the onboard
communication radio to carry the measurements to a central processing
system. Sometimes these systems are installed on electrically powered
material moving equipments so we have to contend with high drive currents
coming off the same battery where we get our power. These drive systems
typically have their own stringent grounding rules to keep the motor
controller alive. To top it all off, in high humidity environments, low
level contaminants add additional and unintended current paths. We have
developed a set of rules and methodology that works, but it is hard to
explain why we do some of the things we do without getting into a lot of
seemingly useless minutia.

I did a miserable job of relating a sub-set of the rules we have to follow
into the boating environment; you provided a much more useful description.

Mark Browne

Electric Grounding - steel hull
 

Thanks, Mark:

I think I have a good theoretical understanding of the issues. I have
some practical experience with electric systems on boats connected to
various shore systems around the world. You obviously have far more
practical experience.

So, I ask, what would you do with Fintry's grounds? Nothing from the
shore comes past the isloation transformers. Clearly the green wire is
grounded to the hull, no question there. On the DC side do we float
or ground the negatives? On the AC side, do we ground the neutral
(the center of the 240, as in common US single phase practice)?

Of course, when I say "ground", I mean at a single point, in so far as
it is possible. This would include insulating steel appliances from
the steel deck and taking other precautions against ground loops.

Issues:
On the DC side, I think I have everything isolated. It may be that
the engine starting circuits will be grounded negative, but the 24VDC
house loads can all be isolated.

Radios are always a question. I think the antenna ground on the SSB
is isolated from the negative power supply, but I'm not sure. If not,
the 12VDC system negative may have to be grounded to the hull, because
we certainly want the antenna counterpoise grounded (or can it be
capacitively coupled?)

On the AC side, I look at big ship practice and think that it makes a
lot of sense. Then I read of the dangers of floating systems and I
come back to earth, so to speak....

What would you do?




Details:

79', 150 ton steel hull and deckhouse, aluminum wheelhouse.

Five diesel prime movers:
New Cat 3406 main
Perkins 6-354 for hydraulics, pumps, alternator (old genset engine)
Two new Northern Lights 9kw 120/240VAC 60Hz 1ph gensets
Hatz single cylinder, rope start, for fire and bilge pump.

Four DC systems:

Engine starting -- one 24DC bank, isolated from everything else -- all
four engine alternators charge it while running. (Lest anyone worry
about single point failures, the 6-354 auxiliary has a spring
starter).

24VDC house system -- one big battery bank, charged by the Cat and the
Perkins (2x125A 24VDC Electrodyne brushless alternators on each
engine), as well as 240VDC universal chargers (paired for redundancy).
This system is mostly for boat operation -- electronics, nav lights.
This also drives two big inverters to power 120/240VAC house loads
while underway.

24VDC emergency system -- battery bank on upper deck, for spare nav
lights, electronics, emergency lights in the event of a main system
failure (fire in the engine room, etc.) Charged by battery charger and
by a diode off house system.

12VDC for radios -- You can't buy a VHF or SSB (except commercial
units at 4x prices) that runs off 24VDC, so we have to do both. I
love 24VDC, but hate the fact that as a practical matter, it means you
have to have both 12 and 24. Batteries on the upper deck (they're also
needed in emergency), charged by 240VAC charger. I chose this way,
because a 30A 24VDC-12VDC converter and spare for the SSB would be
more money and the 12VDC battery capacity would have to be there for
emergency use anyway.

120/240 VAC 1phase for hotel loads, major auxiliaries (pumps, air con,
etc.).

Isolation transformers on shore power. Whether shore power is 120 or
240, we'll use the transformers to create the usual US system --
hot-neutral-hot, 120/240.

In 50hz places we'll use 50hz wherever we can (lighting and air con,
for example) and supply 60hz from a universal battery charger taking
in 230VAC 50hz going to 24VDC back to 120/240 60hz. Except for bussing
both 50 and 60hz, the AC side is pretty conventional.



Jim Woodward
www.mvfintry.com



"Mark Browne" wrote in message . net...
Jim,

Thanks for an excellent and thoughtful post.

I frequently work with systems that have multiple nested grounding system.
We try to reconcile the competing interests of UL safety requirements, FM
intrinsically safety requirements, analog measuring circuits trying to
resolve 0.1 microvolt out of 10 millivolts riding on a 2.5 v differential
load cell output (multiple summed load cells in the system), and the onboard
communication radio to carry the measurements to a central processing
system. Sometimes these systems are installed on electrically powered
material moving equipments so we have to contend with high drive currents
coming off the same battery where we get our power. These drive systems
typically have their own stringent grounding rules to keep the motor
controller alive. To top it all off, in high humidity environments, low
level contaminants add additional and unintended current paths. We have
developed a set of rules and methodology that works, but it is hard to
explain why we do some of the things we do without getting into a lot of
seemingly useless minutia.

I did a miserable job of relating a sub-set of the rules we have to follow
into the boating environment; you provided a much more useful description.

Mark Browne

Electric Grounding - steel hull
 

I could give some off-the-cuff comments on marine wiring, but a proper
answer could easily run to several pages. Fortunately, this topic has
already been explored extensively by many writers. I will defer to these
writings.

Here is one of my very favorite links (simple and fairly complete) on marine
wiring:
http://www.sailmail.com/grounds.htm

This page is one of the best compendiums of boating electronics you are
likely to find. It offers advise on proper marine grounding. I would
recommend printing the entire thing out and reading it a few times as a
practical starting point for any anyone starting out working one their own
marine wiring systems.
http://www.geocities.com/bill_dietri...lectrical.html

The communications world has spent a great deal of time and energy trying to
shield communications systems to prevent a "black hat" from learning what is
happening inside a computer. The buzzword here is "Tempest". One of the keys
is effective shielding and grounding schemes. If your system is designed to
tempest standards, you can be reasonably certain that it in well shielded
and grounded. See this page for a good tutorial and links. Pay particular
attention to the links to mil-handbooks on grounding.
http://www.tscm.com/TSCM101tempest.html

Radio interference, that darn buzz coming out the speaker, can be one of the
most maddening and difficult problems to cure. The rules for radio shielding
a and grounding are way beyond magic. A tiny gap a few inches long look like
a gaping hole in a case. A dead short in a stub cable can flood an entire
system with standing waves. Changing the length of a bonding strap a few
inches can make it entirely useless in RF grounding situations. This stuff
can be sorted out if you are a skilled electronics engineer. (I am) Failing
this, adherence to good practice and a little experimentation can often
produce acceptable results. Leaning what sort of things to try and what has
worked for others is a good staring place for the beginner. Kimmel and Gerke
are consultants that help people cure difficult interference problems. My
company has retained their services on particularly difficult problems. I
find their "bullets" to be a valuable resource.
http://www.emiguru.com/kgb/kgblist.htm

Do you have any favorite reference(s) on marine electronics?

Mark Browne


"Jim Woodward" wrote in message
om...
Thanks, Mark:

I think I have a good theoretical understanding of the issues. I have
some practical experience with electric systems on boats connected to
various shore systems around the world. You obviously have far more
practical experience.

So, I ask, what would you do with Fintry's grounds? Nothing from the
shore comes past the isloation transformers. Clearly the green wire is
grounded to the hull, no question there. On the DC side do we float
or ground the negatives? On the AC side, do we ground the neutral
(the center of the 240, as in common US single phase practice)?

Of course, when I say "ground", I mean at a single point, in so far as
it is possible. This would include insulating steel appliances from
the steel deck and taking other precautions against ground loops.

Issues:
On the DC side, I think I have everything isolated. It may be that
the engine starting circuits will be grounded negative, but the 24VDC
house loads can all be isolated.

Radios are always a question. I think the antenna ground on the SSB
is isolated from the negative power supply, but I'm not sure. If not,
the 12VDC system negative may have to be grounded to the hull, because
we certainly want the antenna counterpoise grounded (or can it be
capacitively coupled?)

On the AC side, I look at big ship practice and think that it makes a
lot of sense. Then I read of the dangers of floating systems and I
come back to earth, so to speak....

What would you do?




Details:

79', 150 ton steel hull and deckhouse, aluminum wheelhouse.

Five diesel prime movers:
New Cat 3406 main
Perkins 6-354 for hydraulics, pumps, alternator (old genset engine)
Two new Northern Lights 9kw 120/240VAC 60Hz 1ph gensets
Hatz single cylinder, rope start, for fire and bilge pump.

Four DC systems:

Engine starting -- one 24DC bank, isolated from everything else -- all
four engine alternators charge it while running. (Lest anyone worry
about single point failures, the 6-354 auxiliary has a spring
starter).

24VDC house system -- one big battery bank, charged by the Cat and the
Perkins (2x125A 24VDC Electrodyne brushless alternators on each
engine), as well as 240VDC universal chargers (paired for redundancy).
This system is mostly for boat operation -- electronics, nav lights.
This also drives two big inverters to power 120/240VAC house loads
while underway.

24VDC emergency system -- battery bank on upper deck, for spare nav
lights, electronics, emergency lights in the event of a main system
failure (fire in the engine room, etc.) Charged by battery charger and
by a diode off house system.

12VDC for radios -- You can't buy a VHF or SSB (except commercial
units at 4x prices) that runs off 24VDC, so we have to do both. I
love 24VDC, but hate the fact that as a practical matter, it means you
have to have both 12 and 24. Batteries on the upper deck (they're also
needed in emergency), charged by 240VAC charger. I chose this way,
because a 30A 24VDC-12VDC converter and spare for the SSB would be
more money and the 12VDC battery capacity would have to be there for
emergency use anyway.

120/240 VAC 1phase for hotel loads, major auxiliaries (pumps, air con,
etc.).

Isolation transformers on shore power. Whether shore power is 120 or
240, we'll use the transformers to create the usual US system --
hot-neutral-hot, 120/240.

In 50hz places we'll use 50hz wherever we can (lighting and air con,
for example) and supply 60hz from a universal battery charger taking
in 230VAC 50hz going to 24VDC back to 120/240 60hz. Except for bussing
both 50 and 60hz, the AC side is pretty conventional.



Jim Woodward
www.mvfintry.com



"Mark Browne" wrote in message
. net...
Jim,

Thanks for an excellent and thoughtful post.

I frequently work with systems that have multiple nested grounding
system.
We try to reconcile the competing interests of UL safety requirements,
FM
intrinsically safety requirements, analog measuring circuits trying to
resolve 0.1 microvolt out of 10 millivolts riding on a 2.5 v
differential
load cell output (multiple summed load cells in the system), and the
onboard
communication radio to carry the measurements to a central processing
system. Sometimes these systems are installed on electrically powered
material moving equipments so we have to contend with high drive
currents
coming off the same battery where we get our power. These drive systems
typically have their own stringent grounding rules to keep the motor
controller alive. To top it all off, in high humidity environments, low
level contaminants add additional and unintended current paths. We have
developed a set of rules and methodology that works, but it is hard to
explain why we do some of the things we do without getting into a lot of
seemingly useless minutia.

I did a miserable job of relating a sub-set of the rules we have to
follow
into the boating environment; you provided a much more useful
description.

Mark Browne

Electric Grounding - steel hull
 

"Mark Browne" wrote...
trimmed
http://www.sailmail.com/grounds.htm
http://www.geocities.com/bill_dietri...lectrical.html
http://www.tscm.com/TSCM101tempest.html
http://www.emiguru.com/kgb/kgblist.htm

good resources, thanks Mark.

-rick-