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Boat wiring

I wish to rewire my 70ft narrow boat but cutout alot of the wire used. Can I run + & - 12 volt lines the full length of the boat & have fuse boxes in each area. The main line would be fused back at the battery for the largest output which would be a bowthruster. Would this pass the boat saftey or not?

Asked by: Trevor James Lewinton  | 11.33am, Tuesday 13 May

WW says:

The system you propose is similar to the ring main used for house wiring, and will work fine for the DC supply. In fact it is likely that everything will work better than if wired individually since there will be virtually no volt drop for the smaller loads.
It is important to use large enough cable for the ring, if you have appliances that can draw high starting currents such as electric fridges and macerator toilets, it will probably need to be at least 25 mm sq. The effective cable size is doubled and the volt drop halved since the current can flow both ways. If the loads are not too high you might get away with 10 mm sq cable (or by doubling the voltage to 24V).
To pass the BSS checks; the ring circuit must pass through an isolator and be fused close to the batteries. Fitting smaller fuse boards at strategic points around the boat will enable all individual circuits to be suitably fused.

Rupert Smedley  | 11.03PM, Tuesday 13 May

I have just re-read your question and noticed the mention of a bow thruster. You will not manage to power a bow thruster, which demands extremely high currents, through cables running the length of the boat due to the voltage drop.
There must be a local battery to act as a reservoir to drive the bow thruster. The best solution would be to use a battery to battery charger, supplied from the ring main, to charge the bow thruster battery.

Rupert Smedley  | 11.16AM, Wednesday 14 May

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