Cable Size & Circuit Protection Calculator

Undersized cable is one of the most common mistakes in 12V, 24V and 48V DC systems - and one of the most dangerous. Too-thin cable causes excessive voltage drop, wasted power, and heat build-up that can damage equipment or create a fire risk. Use this calculator to find the cable size and fuse rating we would recommend for your setup.

 

Select from Inverter or DC load (use for Solar also), enter your voltage, load and cable run length, and the calculator will recommend a cable size that keeps voltage drop within safe limits while ensuring your circuit protection is correctly matched.

 

If you need more information on how to use this calculator, check out the full article on Cable & Circuit Protection Sizing over here. 

 

Load type

Continuous watt rating of your inverter

Continuous current draw of the DC load

One way — voltage drop uses round trip (2×)

3% recommended for most installs

NB. When calculating DC-DC charger input cable sizes, increase input load current by 10% compared to output charge current.

Out of range. Cable run over 6 metres? That's longer than a typical inverter installation. At this length, we'd recommend getting in touch so we can make sure you're getting the right cable and circuit protection for your specific setup. Contact us here or call 08 6205 6868.

Max current

—

—

Recommended fuse

—

Next standard size above max current

Recommended cable

—

—

Cable comparison

Showing recommended cable plus 2 sizes smaller and 2 larger. Voltage drop calculated at max current. Ampacity checked against fuse size (the fuse protects the cable).

Cable Area (mm²) Rated amps Est. V drop Est. % drop Passes
Assumptions: Copper cable only. Resistance calculated at 0.01724 Ω·mm²/m (20°C). Ampacity ratings are a general guide — derate for bundled cables, high ambient temps, or runs inside conduit. Fuse protects the cable, not the load — always fit fuse as close to the power source as practical. Results are a guide only; verify by dropping us a line, with a qualified auto electrician or to AS/NZS 3001 for caravan and marine installations.

Shop Wiring & Protection

CablesCables Circuit BreakersCircuit Breakers Fuses & Fuse BlocksFuses & Fuse Blocks