Cables, fuses and the safety lines you don't cross

Low-voltage doesn't mean low-risk. The non-negotiables.

12V is safe to touch — but 12V systems move *big currents*, and big currents through thin cable mean heat and fire.

Cable sizing: at 12V, a 300W load pulls 25A. That needs 6mm² cable for short runs, fatter for longer ones. When in doubt, go a size up; voltage drop also steals your power.
Fuse every battery positive within 30cm of the terminal, rated for the cable it protects (not the load). Batteries — especially lithium — can dump enormous current into a fault.
Isolator switches between panel→controller and battery→loads, so you can work on the system dead.
Connectors: use proper MC4 connectors for panels and crimped ring terminals on batteries. No twisted-wire-and-tape.
Lead-acid needs ventilation (hydrogen gas when charging).

The hard line: anything 230V and fixed — house wiring, consumer units, grid connection — is qualified-electrician territory, legally and practically. DIY territory is the 12/24V side and plugging appliances into your inverter's sockets.

From EcoPowerful — plain-English DIY solar & wind guidance for UK homes, with a free instant system plan builder. Guidance is general; 230V fixed wiring always needs a qualified electrician. Last updated 2026-06-13.