Is your battery negative earthed?

nigelmercier

nigelmercier

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Is your battery negative earthed?


The topic of GIs has come up again, so I thought it may be interesting to find out what percentage of boats have the battery negative connected either directly or indirectly to shore power earth.

If you are not sure, see if you can light a low wattage 12V bulb (thanks Vic) between your +12V and the earth pin on a mains socket. Only do this is you know which one is earth!

Buggerit! This was meant to be a poll, but the option vanished as I was posting.
 
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nigelmercier said:
The topic of GIs has come up again, so I thought it may be interesting to find out what percentage of boats have the battery negative connected either directly or indirectly to shore power earth.

If you are not sure, see if you can light a low wattage bulb between your +12V and the earth pin on a mains socket. Only do this is you know which one is earth!
Click to expand...

Are you suggesting it should be earthed in this way..... Or not?
 
nigelmercier said:
Is your battery negative earthed?


The topic of GIs has come up again, so I thought it may be interesting to find out what percentage of boats have the battery negative connected either directly or indirectly to shore power earth.

If you are not sure, see if you can light a low wattage bulb between your +12V and the earth pin on a mains socket. Only do this is you know which one is earth!
Click to expand...

mine totally separate
 
Having a steel boat my 12VDC is totally seperate from any connection to the hull.

My mains/shore power earth is connected to my hull via a GI.

One of the things I have always questioned is who is is recommended that the mains/shore power earth be connected to the metal fittings on a GRP boat when in effect a GRP boat is like any double insulated mains power appliance.

On a steel /aluminium boat a live short to the hull could cause the hull to be live and thus give a shock to any person on board but on a GRP boat this would IMHO not be possible unless every metal fitting was connected together. This seems to be to create a potential problem that was not there in the first place.


Different types of boat material need different electrical arrangements IMHO.
 
Mine is earthed but I also have Galvanic Isolator in mains earth. Not seen any untoward corrosion and the Anode tends to be about 1/3 - 2/3 eroded after 12 months afloat so its doing its job fine.

Personally would prefer the 12v -ve not to be connected to mains earth but this is how the boat came and as its not causing any issues that is how it will stay.
 
On the old boat, mains is not connected to anything else. In effect, it's a long two-socket extension lead with a circuit breaker in it.

On the new boat, who knows? :) Investigating the seemingly endless spaghetti wiring is on my list :D

Pete
 
Lazy Kipper said:
What is the main reason for connecting the earth to the -ve? Is it safety?
Click to expand...
Yes it is for safety. I suppose a parallel might be the earthing of things like a metal kitchen sink in the home.
There are however almost as many arguments against as there are for.

Iso 13297:2000, which is/was the relevant standard however does allow for the earth and the DC negative not to be bonded provided a "whole craft" RCD is fitted.

I have been lead to believe that this concession will not be included in the next edition of Iso 13297, which may in fact already have come into effect.
 
I suppose a shore power battery charger might be one place DC and AC earths might come together. I stuck an isolation transformer into the AC lines to my battery charger just to make sure DC and AC earths stayed separate. (plastic boat).
 
VicS said:
Yes it is for safety. I suppose a parallel might be the earthing of things like a metal kitchen sink in the home.
There are however almost as many arguments against as there are for.

Iso 13297:2000, which is/was the relevant standard however does allow for the earth and the DC negative not to be bonded provided a "whole craft" RCD is fitted.

I have been lead to believe that this concession will not be included in the next edition of Iso 13297, which may in fact already have come into effect.
Click to expand...

In the home, the idea of earthing the kitchen sink and other pipework is to avoid the pipework becoming live if there's a fault but, with many new houses having plastic water pipes (as in our boat) is it still relevant? I would rather be holding an unearthed steel tap if the kettle has become live when I pick it up.

I've argued the boat earthing situation with various people but, with so many varying opinions and my limited knowledge, it's hard to decide who's right or wrong. In our case the battery neg is connected to the anode but shore power is an isolated circuit via an RCD.

Some people state that shore power earth and neutral should also be joined on the boat but this could prove lethal in situations such as we now have in the boat yard with European 2 pin shore connection which has a 50/50 chance of being reversed.
 
GrahamM376 said:
In the home, the idea of earthing the kitchen sink and other pipework is to avoid the pipework becoming live if there's a fault but, with many new houses having plastic water pipes (as in our boat) is it still relevant? I would rather be holding an unearthed steel tap if the kettle has become live when I pick it up.

I've argued the boat earthing situation with various people but, with so many varying opinions and my limited knowledge, it's hard to decide who's right or wrong. In our case the battery neg is connected to the anode but shore power is an isolated circuit via an RCD.

Some people state that shore power earth and neutral should also be joined on the boat but this could prove lethal in situations such as we now have in the boat yard with European 2 pin shore connection which has a 50/50 chance of being reversed.
Click to expand...


Leave it as it is then .... it'll save the trouble and expense of fitting a galvanic isolator.

If a fault occurs that would make the DC system/ engine block/ anodes live it will trip the RCD anyway because more than enough current will flow out via the anodes and sterngear to do so.
 
So just to be clear, currently we have 230v mains to sockets with RCD and two MCB's but no mains earth to 12v -ve link, and obviously no GI. What merrit is there in linking mains to 12v -ve? I realise I'd then need a GI.
 
Hi,

I thought I would piggy back on this as it's connected. I was planning on fitting a GI as I was advised to. The boat in question is an all wood boat that is fitted with a 240 RCD from the shore power inlets.

Questions are, do I need to install a GI on a wooden boat and secondly where do I bond the 240v earth to? I'm sure I've read it's possible to connect to the 12dc earth (which in this case is the engine block - through to the water via the prop) - is that right?

Many thanks in advance.
 
OldLady said:
Hi,

I thought I would piggy back on this as it's connected. I was planning on fitting a GI as I was advised to. The boat in question is an all wood boat that is fitted with a 240 RCD from the shore power inlets.

Questions are, do I need to install a GI on a wooden boat and secondly where do I bond the 240v earth to? I'm sure I've read it's possible to connect to the 12dc earth (which in this case is the engine block - through to the water via the prop) - is that right?

Many thanks in advance.
Click to expand...

The link earlier to Iso 13297 spells it out. No difference between wood and GRP as far as the shore power installation is concered AFAIK.

If the shorepower earth is bonded to the DC negative and/or more importantly the anodes then a GI is next to essential if you leave the boat plugged in to shorepower for prolonged periods, even if its not actually in use. If the shorepower is not bonded as recommended an RCD in the incoming power supply is essential but you do not need a GI


Make sure none of the wiring carries DC current and the current to/from anodes.

There is a problem with anodes on a wooden boat but you are no doubt aware of that
 
After tinkering with UK electrics would like to say that it's better to keep 240V ac system separate from boat's 12V DC (apart from charger as needed) and avoid problems. RCD in shore input for safety is all that's necessary. Grounding the boat with the whole marina is illogical for me :confused:
Some of EU electrical ideas I suffered at home - and some are contrary to science :eek:
 
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There are a few suggestions either way and directives it seems encouraging certain set-ups with grounding the 240v with the 12v negative.

I just wanted to try and be clear that with my boat, all wood, it has 240v 16a plug in, connected direct to an 240v RCD - this powers the Victron combi and calorifier. Now the boat will spend occasion stints on shore power, is it best to fit a GI and connect the 240v earth from the RCD to the 12v ground (engine,propgear) or is that not a necessary expense?

Thanks again.
 
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