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The arteries of the system — and its smoke alarms
Cable is rated by cross-section in mm², and the physics is unforgiving: current through resistance makes heat, and resistance rises as cable thins or lengthens. Undersized cable at 12V doesn't just risk fire — it silently steals power as voltage drop, which is why low-voltage systems use surprisingly fat cable (a 300W load at 12V is 25A; the same load at 230V is 1.3A).
A fuse is sacrificial cable-protection: a deliberately weak link that melts before your wiring does. The rule that prevents most DIY fires: the fuse protects the *cable*, so its rating matches what the cable can carry — and it lives within 30cm of the battery's positive terminal, because everything downstream of an unfused battery is a potential arc-welder. Isolator switches on the panel side and load side complete the safety set: you must be able to make the system dead to work on it.
What you'll actually buy: MC4 connectors (the universal weatherproof panel plug — buy a £12 crimping tool, it pays for itself), 6mm² solar cable (~£1.50–2.50/m, the panel-run standard), 10–25mm² battery cable for inverter runs, MIDI/ANL/MRBF fuses with holders (£8–20 — MRBF mounts straight on the battery terminal, elegantly satisfying the 30cm rule), Anderson connectors for quick-disconnect portable kit, and busbars (£10–25) once more than two things connect to a battery. 12V Planet and auto-electrical suppliers are the natural homes for all of it.
Nobody photographs their cabling for the internet, but it's where system quality actually lives — most DIY solar failures and all the scary ones trace back to thin cable, missing fuses or loose crimps. Budget £70–160 for this layer and the hours to do it neatly; it's the difference between a system and a hazard.
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.