Power · Design for safety and code · power-18

Plan overcurrent protection and isolation

Every conductor needs a fuse or breaker sized to protect it, and every energy source needs a way to switch it off safely for maintenance.

How

Put a main fuse or breaker close to the battery positive terminal. For lithium banks, at least one fuse must have an interrupt rating at or above the bank's maximum short circuit current.
Fuse each inverter, controller and load circuit individually in the positive cable. Do not rely on one big fuse for everything.
Use DC rated fuses, breakers and switches with voltage and current ratings that suit the circuit. AC rated parts can fail to break a DC arc.
Fit disconnects for the PV array, the battery, the inverter and the generator. Label each one clearly.
Example (US NEC 706): energy storage disconnects must be readily accessible, within sight or lockable, and labelled. Overcurrent devices are generally rated at least 125% of the storage system's nameplate current.
Example (international): IEC 62548-1 sets design requirements for PV array wiring, protection, switching and earthing, including arrays connected straight to batteries.
Example (US NEC 690.11): PV DC circuits on or in a building at 80 V DC or more need a listed PV arc-fault circuit interrupter, unless run in metal raceway, metal-clad cable or underground.
Example (US NEC 690.12): PV circuits on or in a building need a rapid shutdown function, off grid too. Ground-mount conductors entering a building that only houses PV equipment are exempt, which favours a separate power shed.

Safety: Opening DC circuits under load can draw a sustained arc. Switch off loads and use the correct disconnect before removing fuses.