Earth wiring on new Shore Power

[asj1]

To avoid trailing wires and extension leads tomorrow I intend to fit shore power to my Fulmar. This will be relatively simple with a "consumer unit" with RCD and MCB's and two sockets one of which will be dedicated to the battery charger and one of which will be for a single socket to be used as required. I am happy with the wiring and everything I have bought.
My query is the wiring for the earth. I have read that this must be wired into the 12v negative, but I have also been told to wire the 240v earth to the earthing point on the engine block.
Questions:
1) where should I wire the earth to, the block or the negative side of one of the batteries
2) from where in my 240v circuit should I take this wire to the earth, does it matter? It would be shortest and tehrefore easiest to take it from teh earthing point on on the socket being used for the battery charger.

I am not going to fit a Galvanic isolater as I don't intend to leave shore power permanently connected.

Regards

 

[ms1]

I dont actually think it matters where you connect into your boats earth bonding provided it is a point which is permenently connected.
There is actually an argument that casts some doubt on the widom of this. It goes along the lines of " why would you want to connect your boat earth bonding to every other boat in the marina" .... in the connext that your neighbours electrical problems might burn themselves out through your anodes. I believe that the method you propose to adopt is the prescribed method ... it is an interesting debate. I am sure there are forumites who know much more than I on the matter

 

[SolentPhill]

I can only help in a small way.

I have recently had a electrician on my boat to go through a few problems, he was very good spent 2 hours and really sorted the problems I had.

I am happy to email his number as when you have completed your jobs he can check them for you its well worth it. if your Solent based

I did ask him about earth and he pointed me in the direction of the panel and checked that the earth was shared with both 12 and mains, all metal items around the boat are earthed and my earth leakage RCD was checked.

 

[VicS]

I agree with both Martin1001 and DoralPhill. The point being that all the metal lumps and the 12v negative (assuming you do not have a +ve earth system!) should be connected to the shore power earth, and by cabling which will safely carry the full current allowed by the shorepower supply circuit breaker. Sometimes, for reasons I do not know, the battery isolation switch is in the battery negative lead. In cases like that connecting directly to the battery negative would lead to an unsatisfactory situation when the battery was switched off.

So then the answer is to connect the shore power earth to the heavy negative lead between the battery (or isolator if it it is in the negative supply) and the engine. It may be more convenient to go to the engine end or the other end. I do not see that it matters. It could go to another point on the engine block but you would have to be certain that the connection was sound and remained so. At least the connections of the battery -ve lead are in effect thoroughly tested evey time you start the engine.

Now someone is going to raise the point that in some cases the negative connection to the battery from the starter and alternator etc are isolated from the engine block. Perhaps they will tell us the solution in that situation.

<<from where in my 240v circuit should I take this wire to the earth, does it matter >>

The connection should ideally be directly to the earth connecton in the consumer unit.

 

[SlowlyButSurely]

I think the crucial thing is to connect it to something that's actually earted to the anodes or a grounding plate so that when the earth on the pontoon fails and you simultaneously have a fault on-board it will actually trigger the RCD rather than simply amking your 12v system live with 240v.

 

[sailorman]

strongly suggest you dont connect 12v & 240v in any way keep totally seperate.
the shore power is procted via the RCD

 

[VicS]

[ QUOTE ]
strongly suggest you dont connect 12v & 240v in any way keep totally seperate

[/ QUOTE ] That is a popular idea but the "official" line now is that the 12v sytem sould be earthed to the shorepower earth.

It is difficult to see the situation in which this is important. One posibility might be that a fault in a battery charger, that being the one piece of eqipment on board that is connected to both the 12v and the 240volt systems, could make the 12v system live. In many cases this would trip the rcd because there is already a path to earth from the 12v system via the anodes or the sterngear but not all boats have anodes and a flexible coulping to the propshaft will break that path. So in the event that the 12v system does remain live at 240v you have a situation where there is 240v between the 12v system and any earthed 240v eqipment. Ok if you grab hold of the two the RDC should still protect you but they do fail and then you will be electrocuted. If however the 12v system was earthed the fuse will blow or the circuit breaker trip even if the rcd does not.

I'm sure I can think up some other examples if pushed hard enough. They would all be unlikely to occur in reality perhaps but that's the stuff nasty accidents are made of.

Sorry some of that is badly worded but I hope you can see what I am getting at.

 

[asj1]

Sailorman,
So are you saying simply don't connect the 240v earth to anything ?
Surely the point is that it has to be connected back to the ground (water in our case) in some way. If not why bother with an earth in the first place?

Regards

 

[sailorman]

Happy Birthday /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif

 

[VicS]

TNX