If you are not sure or familiar with electrics, use a professional boat electrician. Read our Electrics Chapter
to familiarise yourself with the potential dangers of getting this wrong. Voltage drop is a key consideration for all DC wiring runs and not killing someone by electrocution is a key consideration when running AC cabling.
What we will say here is that your time spent designing your layout, combined with squaring away your requirements based on what is feasible will really pay dividends at this point. You really do not want to be approaching the laying of electrical cabling without any idea of how you want, or are able, to use your boat.
Buy cable by the reel in the specification required for the job it has to do.
When running cable in conduit, remember to allow for looped tails for connection to appliances such as lighting and sockets. Don’t scrimp on the loops. Trust us when we say it’s easier to make connections when you have a bit of cable to work with.
Clip the cables in accordance with the BSS and RCD. Label everything. Colour and alphabet coded cable markers are available that can be either shrink wrapped or clipped over cables. At the very least use masking tape marked with what the wire relates to.
On you DC system in particular you will have an awful lot of red and black cable loops and ends in different gauges that will need connecting to something so it’s a good idea to exercise good housekeeping in this area at least.
One fitter we know of has a booklet detailing every connection of both his DC and AC wiring circuits. His boat was separated into the main areas from bow to salon to dinette to galley, bathroom, bedroom and engine room/stern.
All the zones then are split further into AC and DC, port and starboard. Further coding is given to individual components within the scheme such as sockets, switches, pumps, lighting and appliance feeds. So a schematic coding can be developed that may read 2D4PLC3 in a schematic diagram. This could stand for 2 (salon) D (DC) 4 (4mm cable) P (port) L (light) C (ceiling) 3 (third one along) and the cable feed to and from the fuse/distribution box would be labelled the same.
This attention to detail is not applied by everyone but it does mean that a labelled cable can be instantly identified and any faults traced back to the distribution box efficiently. Time spent here in the design and layout of the system will certainly save time and effort in the long run.
Good electrical practise would advise testing of all cables before they are connected to appliances and loads i.e. before the second fix. Continuity testing will detect broken conductors and faulty terminals. A Mega test or insulation resistance test will test the integrity of the insulation. This is a professional task that requires specialist equipment and involves running voltage down the cable in order to measure resistance. Failure of the test indicates a break in the insulation caused say by a trapped wire or a screw through the harness.