how to wire a narrowboat – part 5

how to wire a narrowboat - part 5

first the rules, the 'it must be like this' bit

Now we get down to the rules that have to be followed so the wiring is done to meet the RCD requirements and recommendations.

cable insulation colours

Black cable may only be used for negative cables and the cable must be the same colour throughout its entire length – so if it is a negative it must be black all the way, not a red with a bit of black at each end

If the boat has a three-phase AC system (unusual with our boats but possible) the black is used for an AC live so yellow should be used for all the negatives not black.

Positive cable – a positive cable (battery volts) may be any colour except

  • Black,
  • Brown,
  • Blue,
  • Green,
  • Green/yellow,
  • If a 3 phase boat yellow because that will be negative.

recommendation or good practice

Red is used for all positives except switch positives i.e. the wires between two 2-way switches; the cable from the switch to an item (light, pump etc) should be a different colour to red. The means when testing if it is red it should be at battery volts, any other colour that is allowed to be a positive that will need a switch switched to be at battery volts.

back to the rules:

securing cables and what can run with what or not run with what

All cables should be secured every 300mm, unless they are supported in a conduit or ducting. Where there are only DC cable in the duct they do not need to be secured, if other cables are also in the duct, AC for example, secure every 300mm to keep the two cable types at least 100mm apart.

DC cables should not be run within 100mm of AC cables or gas pipes unless protected in a conduit. (Recommendation I tend to use split-corrugated conduit secured every 300mm to 1000mm) within the duct.

To make this clearer there are two situations

  • A Gas Pipe in the picture

All cables closer than 100mm to a gas pipe have to be in conduits be they AC or DC.

  • No Gas pipe in the picture

If AC and DC cables are closer than 100mm one of them has to be in conduit to separate them away from the others.

All cables should be protected anywhere they can be abraded by the vibration of the boat etc, This particularly means where the cable crosses an edge of metal or wood, even plastic, goes through a hole in a bulkhead (wall) be it wood or metal etc or where they cannot be secured at 300mm intervals, conduit must be used.

I think that is about it but anyone shout if I have missed anything


You should now have all the information to purchase the cables you need with the terminations, the correct size of fuse/switch board and do the DC installation of the boat from the Batteries via fuse board to the electrical items.

in the appendix are

  • How two 2-way switches can control things from two different positions.
  • A copy of the full one page drawing of the Lighting circuits
  • A copy of the full one page drawing of the Sockets etc.

Copies of the originals are available from me via the 12 Volt Boating Group 

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About Graham Mills

I have owned boats since I was 10 and have helped other boaters with their electrics for almost sixty years. I sold my last boat in October 2016 as I can no longer singlehand a boat. The result is more time to help others and that has expanded. I have never charged for my help, although now a days as a pensioner I ask boaters to pay my expenses to get to them which can be anywhere in the UK.