Wiring, fusing & protection
The parts every build needs (and most shopping lists forget)
The system builder picks your panels, controller, battery bank, and inverter. But a working system also needs the glue: correctly sized wire, a main fuse, a way to disconnect, a place for all the grounds to land. This is the gear that turns four boxes into a safe, finished install — and it's where most first builds cut a corner they shouldn't.
Solar PV systems involve high-voltage DC and substantial fault currents. Improper installation can cause fire, injury, or death. Consult a licensed electrician and your local Authority Having Jurisdiction (AHJ) before any installation work, and verify every value against the current NEC edition and current product datasheets. Numbers and recommendations on this page are educational starting points, not a substitute for professional design and inspection.
The four you can't skip
- A main fuse on the battery. Between the battery positive and the rest of the system, sized to the wire (NEC 690.8/240). On a LiFePO4 bank a dead short without a fuse is a fire. A Class T fuse is the DIY standard because it interrupts the very high fault current lithium can deliver.
- Wire sized to the current, not to what's in the drawer. Run the ampacity math and add for voltage drop on long runs. Fine-strand welding cable (2/0, 4/0) for battery-to-inverter; smaller tinned wire for branches.
- A disconnect / battery switch. So you can safely kill power to work on the system — and, on multi-bank setups, isolate banks so one can't drain the other.
- A busbar. One landing point for positives, one for grounds. Stacking six ring terminals on a single battery stud is how connections work loose and heat up.
On Blue Sea battery switches
Blue Sea Systems gear is the marine-grade favorite — pricey, but the parts you bolt down once and never think about again. Worth knowing the naming, because it catches people: a plain Dual Circuit switch keeps two banks permanently isolated (no way to cross them over), while a Dual Circuit Plus adds a COMBINE position so you can parallel them in a pinch. If you specifically want the two banks kept apart, you want the non-Plus version.
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Some listings earn us a commission. Sizing guidance is physics and NEC code, never pay-to-play. Always confirm your own ampacity and overcurrent math.