Wire & fuse size calculator

Voltage drop is the volts you lose along the cable. A long, thin cable wastes power as heat and the fridge or inverter can sag. This page aims for a small drop — 3% for important kit, 10% for everyday kit — then picks the next copper size you can buy.

You type the one-way length — battery to the kit. The return cable is just as long, so the calculator uses twice that for voltage drop. A 2 m run is 4 m of cable in the maths.

The fuse protects the cable. If something shorts, the fuse should blow before the cable overheats. Size the fuse a bit above the current you will draw, and not above what that cable can take. The gadget may have its own fuse as well.

Yes. The same watts is about half the amps at 24 V, so you can often use thinner cable. Match the voltage to the leisure system you actually have. Do not mix 12 V and 24 V figures.

A 12 V inverter run can draw hundreds of amps from the leisure battery. That current needs fat, short, flexible copper battery or welding-style cable — not thin chassis wire — and a large fuse near the battery. 24 V roughly halves the amps, so the cable can often be thinner. This page is a planning size, not a wiring diagram.

Copper is assumed. Fridge, pump and solar runs can use ordinary leisure cable. An inverter battery feed assumes thick flexible copper battery or welding-style cable, not thin chassis or thinwall cable. Those thin cables cannot carry inverter amps.

They are larger DC fuses used on fat cables, often next to the battery on an inverter feed. A blade fuse is for smaller runs such as a fridge or pump. The amp figure matters more than the name. This page does not pick a fuse brand.

A thin cable runs hot and wastes power. Lights can dim, a fridge can cut out, and in a bad case the cable can melt. Round up to the next size you can buy. Cable is cheaper than a fire or a ruined weekend.

Either. Watts divided by volts gives amps. For solar, the honest figure is often the current on the panel or controller label, not watts divided by 12 V. You can type that current instead.

Yes. The Inverter DC feed preset uses inverter AC watts divided by battery volts — the usual cable-chart method. It does not also add inverter waste on top. You can always type a different figure.

No. This is a planning estimate only. It is not an electrical design, installation certificate, or a claim of ISO or ABYC compliance. Cable type, temperature, how the cable is run, and the fuse holder all matter. Use a qualified installer for safety-critical work.