Earthing an Inverter

[alan.denby]

Is there anyone who can advise me? I've bought a small inverter, on the back
of which there is a wing nut for the earth wire. The instructions say that
it must be earthed, so the question is how do I earth the inverter on my
narrowboat?

Alan Denby

[Paul E. Bennett]

Post by alan.denby
Is there anyone who can advise me? I've bought a small inverter, on the
back of which there is a wing nut for the earth wire. The instructions say
that it must be earthed, so the question is how do I earth the inverter on
my narrowboat?
Alan Denby

Assuming you have a steel narrowboat then the boat frame would be your best
point. You will need to be careful with exactly how you achieve this. Could
you describe the inverter in more detail as the earth arrangement may have
implications for RF intereference.

[alan.denby]

Post by Paul E. Bennett

Post by alan.denby
Is there anyone who can advise me? I've bought a small inverter, on the
back of which there is a wing nut for the earth wire. The instructions say
that it must be earthed, so the question is how do I earth the inverter on
my narrowboat?
Alan Denby

Assuming you have a steel narrowboat then the boat frame would be your best
point. You will need to be careful with exactly how you achieve this. Could
you describe the inverter in more detail as the earth arrangement may have
implications for RF intereference.
--
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Forth based HIDECS Consultancy .....<http://www.amleth.demon.co.uk/>
Mob: [phone]
Tel: [phone]
Going Forth Safely ....EBA. http://www.electric-boat-association.org.uk/
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Paul,

It's a Nikkai N65AU 300 watts Soft Start, 12v - 230v AC, 50Hz

Alan

[Paul E. Bennett]

Post by alan.denby
Paul,
It's a Nikkai N65AU 300 watts Soft Start, 12v - 230v AC, 50Hz

Sometimes it helps to know the model number. Havinhg had a quick look
around the answer is that the wing nut is the mains side earth connection
which should be attached to the steel of your boat hull by the shortest
possible connection. The earth through the wing-nut is for safety purposes.

I note that someone has already mentioned ensuring use of the right grade
of DC wiring, which will be very important if the inverter is a distance
from your battery.

[t***@strong.org]

Out of interest, what is the generally accepted way of earthing an
inverter on a GRP boat - if any?

--
Tim Strong

[Paul E. Bennett]

Post by t***@strong.org
Out of interest, what is the generally accepted way of earthing an
inverter on a GRP boat - if any?

GRP and wooden boats seem to share quite a number of similar questions. The
answer "it depends" will often be returned. Quite on what I have yet to
fathom. On a GRP or wooden boat there would be no-where to connect the
earth to that would make any sort of sense. One could select the engine as
a potential earthing location, assuming the boat has one. When I have
answered such questions for my own (GRP) boat I will let you know. For the
moment I am going with the float-free regime backed up by RCD's.

[Malcolm]

On Mon, 15 Aug 2005 22:12:43 +0100, "Paul E. Bennett"

Post by Paul E. Bennett
GRP and wooden boats seem to share quite a number of similar questions. The
answer "it depends" will often be returned. Quite on what I have yet to
fathom. On a GRP or wooden boat there would be no-where to connect the
earth to that would make any sort of sense. One could select the engine as
a potential earthing location, assuming the boat has one. When I have
answered such questions for my own (GRP) boat I will let you know. For the
moment I am going with the float-free regime backed up by RCD's.

Hi Paul - long time no speak.

It's been a long time since I worked for Marconi Marine, but my
clouded brain recalls having devises similar to sacrificial anodes -
but something metalic on the outside of the hull - connected through a
bolt to an earthing point inside the hull and thick copper bar.

Some mention has been made of using propellor shaft / propellor - but
I would have thought that would mean rapid corrosion ??.



Malcolm Nixon

[Paul E. Bennett]

Post by Malcolm
On Mon, 15 Aug 2005 22:12:43 +0100, "Paul E. Bennett"

Post by Paul E. Bennett
GRP and wooden boats seem to share quite a number of similar questions.
The answer "it depends" will often be returned. Quite on what I have yet
to fathom. On a GRP or wooden boat there would be no-where to connect the
earth to that would make any sort of sense. One could select the engine as
a potential earthing location, assuming the boat has one. When I have
answered such questions for my own (GRP) boat I will let you know. For the
moment I am going with the float-free regime backed up by RCD's.

Hi Paul - long time no speak.
It's been a long time since I worked for Marconi Marine, but my
clouded brain recalls having devises similar to sacrificial anodes -
but something metalic on the outside of the hull - connected through a
bolt to an earthing point inside the hull and thick copper bar.
Some mention has been made of using propellor shaft / propellor - but
I would have thought that would mean rapid corrosion ??.

Yes Malcolm, it has been a while.

Would anyone drill holes in the bottom of a high class wooden rowing skiff
that happend to have a battery and inverter on board to run a laptop? (I
know it is an unlikely scenario) that was why I said the usual answer is
"it depends".

Generally, so long as there is good isolation, there is little problem in
having a fully floating 230V output with no reference to earth connections.

[Jeremy Nunns]

Post by Paul E. Bennett

Post by Malcolm
It's been a long time since I worked for Marconi Marine, but my
clouded brain recalls having devises similar to sacrificial anodes -
but something metalic on the outside of the hull - connected through a
bolt to an earthing point inside the hull and thick copper bar.
Some mention has been made of using propellor shaft / propellor - but
I would have thought that would mean rapid corrosion ??.

Would anyone drill holes in the bottom of a high class wooden rowing skiff
that happend to have a battery and inverter on board to run a laptop? (I
know it is an unlikely scenario) that was why I said the usual answer is
"it depends".
Generally, so long as there is good isolation, there is little problem in
having a fully floating 230V output with no reference to earth connections.

Much more likely - a classic wooden yacht (or even original wooden
motor cruiser), where you don't especially want to have any bits going
through the hull that you can possibly avoid.

I occasionally use a small (150W) inverter on board such vessels for
laptop or similar fairly low load devices. I try to check for the
'double insulated' symbol on what I'm connecting, and let everything on
the 230V side 'float'.

You could connect the 'Earth' to the 12V Neg, which is *probably*
connected to the engine block which is *probably* connected to the prop
shaft (but on one GRP boat I was on last week, where I expected that to
be true, the Engine power was completely separate from the domestics
power, including the Neg wiring, which surprised me). However,
realistically within an environment that is all insulators - wood,
GRP, furnishings, etc - I would have thought it was better to have the
230V floating. What do others think?

Also, it is possible that some cheap inverters (like the one I have) may
not be very happy with having their Earth connected to their 12V Neg
input, although they *should* be OK.

[Malcolm]

On Mon, 15 Aug 2005 22:42:29 +0100, "Paul E. Bennett"

Post by Paul E. Bennett
Would anyone drill holes in the bottom of a high class wooden rowing skiff
that happend to have a battery and inverter on board to run a laptop? (I
know it is an unlikely scenario) that was why I said the usual answer is
"it depends".

OK point taken - the boats I worked on - well mostly oil rigs /
platforms / ships had good earths - but lifeboats for SOLAS ( Safety
of Life at Sea ) radio - had these things installed when new. But they
don't generally suffer from corrosion of the prop and shaft - as they
spend their live mostly on derricks.

Fancy bobbing up and down on the north sea in one of these things -
part of my memories - trying to talk to Stonehaven Radio on 2182kHz
!!!.

Malcolm

[c***@hotmail.com]

On any vessel - steel, aluminium, wood or GRP - it is worth having a
dedicated earth/ground bar to which any and all earths can be taken and
the battery negative(s) are connected. In my steel vessel the bar is a
25mm x 6mm x 500mm piece of copper bar -
http://www.rmstone.screaming.net/internal/page/image59.html - into
which are drilled a number of M8 and M5 holes. This bar in turn is
firmly bolted to well cleaned and vaselined steel of the hull. If a
hull then requires a ground plate in the sea water, then only a
suitable single cable of reasonable cross section is required to the
plate. I have an earth from the shaft, the earths from radar and
inverters and earth from the AC isolation transformer all connected
together with engine and domestic battery negatives and negative
returns from switch panels. It also makes incorporating a DC shunt
easy - just requires inserting in the approriate battery negative line.

[Graham Brooker]

Post by Malcolm
It's been a long time since I worked for Marconi Marine, but my
clouded brain recalls having devises similar to sacrificial anodes -
but something metalic on the outside of the hull - connected through a
bolt to an earthing point inside the hull and thick copper bar.
Some mention has been made of using propellor shaft / propellor - but
I would have thought that would mean rapid corrosion ??.

Are these outside of hull things "Zinc Fish" that sea going boats tend to
hang over the side when in port to help protect the prop and shaft. There
can also be a doughnut shaped anode clamped on the shaft behind the prop or
on something bolted to the outboard or outdrive.

None of these things are anything to do with safety earthling.

Graham Brooker

[Paul Burke]

Post by t***@strong.org
Out of interest, what is the generally accepted way of earthing an
inverter on a GRP boat - if any?

If there's nothing conductive to connect it to, don't connect it. It's a
safety eart, so on a metal boat you want to make sure that all the metal
acts as a return path to earth. That way, you can't accidentally make
the whole boat live wrt whatever's running from the inverter. #

Remember- there's enoght power, even in a small inverter, to kill you
for the rest of your life.

Paul Burke

[Paul Burke]

Post by alan.denby
Is there anyone who can advise me? I've bought a small inverter, on the back
of which there is a wing nut for the earth wire. The instructions say that
it must be earthed, so the question is how do I earth the inverter on my
narrowboat?

To the steel of the hull. Don't forget that even a small inverter will
be thirsty on the batteries- a 120W one will draw over 10A from your
12V, so size the cables appropriately.

Paul Burke