Guidance on Choice and Use of Cable

Always use the correct size of cable. Attempting to supply large currents through cables of insufficient thickness is bad practice and should be avoided.

See the chart below for guidance.

Always protect circuits with suitable fuses. Calculate the required fuse value and fit that value. If you put in too large a fuse you risk damaging the device supplied or the cable itself. To calculate the value of fuse required, add together the wattage of the lamps or other devices which form the load and divide this total by the voltage (12 volts or 24 volts).

diameter mm
CSA of
Core (mm2)
Resistance per
metre (ohms)
(at 20 deg c)
Cont. Current
Rating (Amps)
Voltage Drop
over 5m (Approx)
at max current
(A) (B) (C) (D) 5 x C x D =
9/030 0.65 0.0294 5.75 0.845v
14/030 1.00 0.0189 8.75 0.827v
21/030 1.50 0.0125 12.75 0.797v
28/030 2.00 0.0094 17.50 0.823v
35/030 2.50 0.0075 21.75 0.816v
44/030 3.00 0.0060 25.50 0.765v