Overload protection downstream of inverter on off grid solar pv system

Few different points there - ADS - i.e. giving protection against electric shock in the case of a L-PE fault, should be fine using RCDs (both RCCBs and RCBOs).

The MCBs and the overcurrent portion of RCBOs, as you correctly say, are unlikely to trip my magnetic operation on L-N faults (except possibly for very low rated ones) - but then the currents are so low, you're really only talking about a decent overload. The thermal element of an MCB, or RCBO (or even a conventional fuse) should be fine to provide overload protection, especially if you don't have reduce c.s.a conductors (i.e. Iz ≥ In). As L-N faults are treated as overloads, you might think twice about situations where the conductors have a lower rating than the protective device - industrial motor circuits with the overload at the motor end is the classic, but also think about the conventional domestic ring circuit.

Note that BS 7671 only has specific disconnection times (0.4s, 5s etc) for ADS - i.e. L-PE faults - for L-N faults and overloads you can take as long as you like provided the conductors (or more accurately their insulation) don't overheat.

   - Andy.

Just to add,, make sure the system has it's own means of Earthing and there's a N-PE link somewhere in the system (some off-grid inverters will include one, but other might not or it might be programmable if the inverter is capable of off-grid, islanded and grid-tied operations.

Few different points there - ADS - i.e. giving protection against electric shock in the case of a L-PE fault, should be fine using RCDs (both RCCBs and RCBOs).

The MCBs and the overcurrent portion of RCBOs, as you correctly say, are unlikely to trip my magnetic operation on L-N faults (except possibly for very low rated ones) - but then the currents are so low, you're really only talking about a decent overload. The thermal element of an MCB, or RCBO (or even a conventional fuse) should be fine to provide overload protection, especially if you don't have reduce c.s.a conductors (i.e. Iz ≥ In). As L-N faults are treated as overloads, you might think twice about situations where the conductors have a lower rating than the protective device - industrial motor circuits with the overload at the motor end is the classic, but also think about the conventional domestic ring circuit.

Note that BS 7671 only has specific disconnection times (0.4s, 5s etc) for ADS - i.e. L-PE faults - for L-N faults and overloads you can take as long as you like provided the conductors (or more accurately their insulation) don't overheat.

   - Andy.

Just to add,, make sure the system has it's own means of Earthing and there's a N-PE link somewhere in the system (some off-grid inverters will include one, but other might not or it might be programmable if the inverter is capable of off-grid, islanded and grid-tied operations.