Choosing wire gauge & fuses

Pick conductor sizes that carry the current without overheating or sagging in voltage, and fuse every circuit to protect the wire.

Wiring is where a lot of otherwise-good builds go wrong. The two things that matter are heat (a wire too thin for its current gets hot and can start a fire) and voltage drop (a long thin run wastes energy and dims your lights). Fuses are the safety net that stops a fault from turning the wire itself into the weak point.

Size for current and length

First find the current a circuit will carry: watts divided by volts. A 600 W inverter on 12 V can pull around 50 A under load — a surprisingly large number that needs a properly thick cable.

Then account for length. The longer the run, the thicker the wire needs to be to keep voltage drop under about 3% for sensitive loads. Low-voltage 12 V systems are far more sensitive to this than 24 V or 48 V, because the same power means much higher current.

Voltage drop is not a safety limit

It's a performance one. The fuse and the wire's ampacity keep the run safe; voltage drop just decides how much energy you waste and how dim your lights get. Size for ampacity first, then upsize if a long run pushes the drop past ~3%.

Rule of thumb

As a starting point on 12 V, pick the cable from what the circuit does. Always check a voltage-drop figure for your exact run length rather than guessing — a long run steps everything up a size or two.

Circuit	Typical cable
Lighting & signal	1.5–2.5 mm²
Sockets & pumps	4–6 mm²
DC-DC charger / solar feed	6–10 mm²
Inverter & main battery	25–70 mm²

Starting points for 12 V DC. Long runs push voltage drop up, so step up a size for anything more than a few metres.

Fuse to protect the wire

The fuse protects the cable, not the appliance. Choose a fuse rating below the safe current-carrying capacity of the wire it protects, and as close to the source (the battery) as practical — the few centimetres between a battery terminal and its fuse are the most dangerous part of any system.

Use a Class-T or MEGA fuse on the main battery positive, and a fused distribution panel for the smaller branch circuits. Every wire that leaves the battery should pass through a fuse sized for that wire.