T1 · Wire check · free

What size wire does this circuit need?

Enter one DC circuit. Circuit Locker sizes it twice, once for voltage drop and once for the federal ampacity table, and gives you the thicker of the two with the largest fuse or breaker the wire may have.

The circuit

System voltage

12 V24 V

Current (A)From the device label

Run, one way (ft)Source to device

Voltage drop limit

3% critical 10% other

3%: panel feeders, bilge blowers, electronics, navigation lights. 10%: cabin lights and similar.

Insulation rating Printed on the cable jacket. Marine boat cable is commonly 105 °C.

Runs through an engine space Inside a multiconductor sheath (duplex or triplex cable)

Current-carrying conductors bundled together Count the wires that carry current in the same sheath, harness, bundle or conduit, this one included (not ground wires). Three or more lower what each may carry (Table 5 note 2).

The wire check is free and unlimited. Saving circuits, printing panel labels and the run sheet come with the Locker Pass, $1.95 a month (free during preview). Pricing

Your answer appears here

Try the worked example: a 7.5 A bilge pump 18 feet from the panel, or a 15 A windlass control 12 feet away.

Run length is one way. The formula counts the wire out and back for you.