Electrical Protection Basics

Protection devices keep people, cables and equipment safe. A solar or backup system needs protection on both the DC side (panels and batteries) and the AC side (inverter output and distribution).

Circuit breakers (MCB and MCCB)

Miniature circuit breakers (MCB) and moulded case circuit breakers (MCCB) disconnect a circuit on overload or short circuit. MCBs cover lower currents; MCCBs are used for higher currents and larger feeders. DC breakers are not interchangeable with AC breakers — DC arcs are harder to interrupt, so use devices rated for the DC voltage of your system.

Residual current protection (RCCB and RCBO)

Residual current devices detect leakage current to earth and disconnect quickly to reduce the risk of electric shock. An RCBO combines residual current protection with overload and short-circuit protection in one device.

Surge protective devices (SPD)

SPDs divert voltage surges from lightning or switching events away from sensitive electronics. Solar systems commonly use a DC SPD between the panels and inverter and an AC SPD at the distribution board.

Fuses and isolators

• PV string fuses protect panel strings from reverse current when several strings are connected in parallel.
• DC isolators allow the PV array to be safely disconnected for maintenance.

Earthing

Protection devices only work as intended with a correctly designed earthing system. Panel frames, mounting structures and equipment enclosures should be bonded to earth.

Selecting ratings depends on system voltage, cable size and fault levels — ask a qualified electrician or the SMART TECH team to review your design.