This is the part of a system nobody photographs and the part that decides whether it lasts.
Size the cable from current, length and drop
Three inputs: the maximum current the load draws, the total length there and back, and the voltage drop you will accept. The result is a cross-section. Run length matters as much as current, which is why a cable that is comfortable at half a metre can be inadequate at four.
Protect every cable that can carry a fault
A fuse or a breaker sized to the cable, as close to the battery as the installation allows, rated for direct current at the system voltage, with a breaking capacity above what the bank can deliver into a short. Everything between the battery terminal and that device is unprotected, which is why the distance is measured in centimetres.
Terminate joints with the right tool
Lugs crimped with a die matched to the lug and the cross-section, not soldered and not squeezed with pliers. Ferrules on stranded wire entering screw terminals. Heat-shrink over the barrel. Every one of these is about excluding air from the joint, because a joint that admits air oxidises and a joint that oxidises heats.
Add an isolator and a way to measure
A means of disconnecting the bank deliberately, and a shunt in the negative line so every amp in and out is counted. Both are installed at the start or retro-fitted awkwardly later, and the second one is what makes every later question answerable.
Know which decisions are not yours to make
Earthing and bonding, notification, and anything that connects to a building’s fixed wiring are governed by the applicable regulations where you live, and they differ between countries and between settings. The manuals govern the products; the regulations govern the installation.
What people ask before they order
Why is the fuse sized to the cable and not the appliance?
Because the cable is what has no protection of its own. A fuse that lets the cable overheat before it opens is not protecting anything, which is why a larger fuse is never an upgrade.
Does this page replace the manuals?
No. Every inverter, charger and controller specifies its own input protection and cable requirement, and where those differ from a general calculation, the stricter one is installed.
Last reviewed 16 September 2026