Low Voltage Electrical Wire Sizing for Boats
Introduction
Deciding upon the correct electrical wire to be used onboard sail and motor boats can be tricky. To often wires designed for alternating current in domestic houses are used instead. That is a bad idea as incorrect sizing can lead to malfunctioning equipment or in worst case fire.
What determines the wire size is not the power nor the voltage but the current (amperage). Current (I) is a function of power (P) and voltage (V) i.e. I=P/V and from this it is seen that lower voltage will at the same power result in higher amperage. That is why a wire used in a domestic house can be used to deliver a lot of power with alternating current at 240V AC but can be dangerous on a boat with 12V DC with even a low power delivered.
The calculator is based on ISO 13297 Small Craft - Electrical System and will help determine the correct wwire size based on current, allowable voltage drop, cable temperature rating, voltage and the maximum current wire capacity is adjusted if installed in engine room and/or if bundled together with other cables. It is only valid for cobber wire.
Voltage drop in the circuit shall be below 10% with all equipment running. In case of essential equipment a voltage drop of no more than 3% is recommended.