A boat's wiring should be designed so that it
comprises cables between terminal blocks, perhaps a terminal block on
each bulthead port and starboard. This allows the wire to individual
lights or appliances to be short and easily installed. Example wiring for engines
Example wiring for
accessories
Each switch panel or control panel should have terminals to provide the interface with the cables to which it connects. This allows the panel to be removed entire from the boat without taking out any cables.
Remember, most wiring on production boats is
installed at a time in the construction when there is easy
access. This often results in wiring that is "built in" and
cannot be removed for repair. No one objects to this, although no
one would allow an engine to be installed this way.
If the voltages to be used are not yet
determined, see What voltage is best? .
Start with an outline drawing of the boat, showing each item to
which wires will attach. Identify bulkheads and other structures
that make access difficult.
Connect the wired items with lines, and label each with the size and
number of wires required, see What codes
need to be followed?. Add an extra 20% to 50% for spares, and
round up to the next larger size of terminal block.
Back at the boat, measure the length of cable that will be needed
between terminal blocks. Add this information to the outline
drawing.
After a survey to establish what circuits will be required, place terminal blocks of appropriate size throughout the boat. A typical solution would place a terminal block at each bulkhead port and starboard, as well as the engine room and the forepeak. The number of connections in each terminal block should be from 20% to 50% greater than the expected need, to allow for future expansion.
A list is made of the needed cables
Each cable is designed to run between two terminal blocks, with each cable built separately from the boat and therefore removable for service or replacement. Figure out how many wires go to each place, and put properly sized terminal blocks at each end of each cable. Then list the wires needed for each cable and measure its required length.
From the outline drawing, create a spreadsheet containing an entry
for each cable needed. For each cable, show the length, number
and size of wires, color codes and/or
labelling, and terminal type. It makes sense to create separate
spreadsheets for primary wiring, engine wiring, and so on. Add
the columns to obtain the materials list. Example planning spreadsheet
Buy the materials. Refer to Where to get materials if surplus items can be used.
Do not begin work until all materials are in
hand.