chasroberts
regular
Reged: 27/02/2004
Posts: 472
Loc: Boat - Med. Me - Austria
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I am redoing some inherited wiring on our fridge and am in a bit of a quandry. Whoever wired this up originally has proceeded as follows:
12V positive direct to the fridge unit from one of the two house batteries through a fuse holder.
12V negative direct from battery to fridge unit through fridge on/off switch.
This obviously means that the positive power to the fridge is permanently on even when the battery switches and the fridge switch are off which I seem to remember is not considered 'good form'.
Is there any reason why the negative side would be switched instead of the positive?
I am considering taking a new positive lead from the battery 1 terminal on the main battery switch through a suitable fuse to the switch and from there to the fridge and leaving the negative from the battery direct which is close by the fridge but obviously removing it from the switch.
Can anybody give me any ideas as to whether this is the accepted method or is there another more elegant idea that might make life simpler and easier.
As always, my thanks in advance to all the panel.
Chas
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'The difference between genius and stupidity is that genius has its limits.' - Albert Einstein.
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MoodySabre
regular
Reged: 24/10/2006
Posts: 3967
Loc: Bradwell and Leigh-on-Sea
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If the switch is on the positive (normal) then the negative doesn't need to go back to the battery but just to ground somewhere convenient. The battery may of course be convenient if the wiring is already there.
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Clinker dinghy in need of some work
Interesting old books
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nedmin
regular
Reged: 12/10/2002
Posts: 890
Loc: north lincs.
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Needs positive to be switched as you suggested. buy a good quality fuse holder and wire as near to the battery switch as poss.
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Evadne
regular
Reged: 27/02/2003
Posts: 4606
Loc: Hampshire, UK
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As long as you break the circuit then the fridge will switch off, but normal practice as you say is to switch the positive side and common the negative sides of all devices to the battery. This is because if you only switch the negative side then if there's a fault there is the potential (sorry) for current to flow through the unswitched positive and out the negative of another appliance when both are switched off. Your plan sounds good, and if you are really paranoid you could switch both positive and negative, and completely isolate the device.
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Elizabethans.
I'd far rather be happy than right.
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chasroberts
regular
Reged: 27/02/2004
Posts: 472
Loc: Boat - Med. Me - Austria
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Many thanks to all for your input. Will give it a whiz this afternoon.
Chas
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'The difference between genius and stupidity is that genius has its limits.' - Albert Einstein.
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wooslehunter
regular
Reged: 31/10/2002
Posts: 1016
Loc: Hants, UK
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Possibly the previous owner thought of isolating everything except the fridge. i.e. leave the boat for a few hrs in the pub but need the fridge to stay cool.
It's a bad idea IMO. In an emergency you want to isolate everything with one switch immediately. Alternatively, you flip the isolator but forget thr fridge. Next time you're on the boat the domestic bank is flat. You can always charge it but it's not a good idea to flatten it completely.
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I always wanted to learn to spell "engineer". Now I are wun.
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VicS
regular
Reged: 13/07/2002
Posts: 9603
Loc: Home: Kent. Boat: Chichester
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Quote:
Possibly the previous owner thought of isolating everything except the fridge
Still does not explain the switch being in the negative .........unless the main battery isolator is in the negative.
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Old Chemists never die, they just fail to react
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whipper_snapper
regular
Reged: 09/08/2006
Posts: 1514
Loc: Kenya
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There is nothing at all wrong with the arrangement you describe; except that it is little unorthodox (which could create a problem if someone modifies it without understanding it)
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