Wiring

Wire size and voltage drop

Undersized cable runs hot and starves the load. Set the amps and the run, and get the gauge, the voltage at the far end, and the fuse.

Updates as you typeSame math as the original Megawatt tool

The circuit

Live
20 A
System voltage
15.0 ft

Measure the wire path from source to load. The math doubles it for the return.

Allowed voltage drop
Where it runs
Wires bundled together

Use this wire

Within limits
Copper area to scale. Dashed ring is 4/0 AWG.

Gauge

6 AWG

Fuse

0A

At the load

0V

0

Voltage drop

0V

Derated ampacity

0A

Drop as the run gets longer

Drop with the chosen gaugeYour limitYour run

Every gauge, checked

How the math works

Required copper area is CM = 10.75 × amps × one-way feet × 2 ÷ allowed drop volts, using the published Megawatt table for 105°C copper. The wire must also carry the current after derating: 85% in an engine bay, and 70%, 60%, 50%, or 40% as more wires share a bundle. The fuse floor is 125% of the load, stepped up to a standard size, and capped at the wire’s derated ampacity.

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