What is surge protection device back up fuse function?

In order to make sure the surge protection device can cut out from the power supply system after the failure, to avoid accidents enlargement; it is not recommended to use miniature circuit breakers instead of fuses.
 

First, tripping the fuse with a precise point, the circuit can be built quickly from tripping device failure, and slightly off a great trip tripping curve range, it can lead to malfunction or not operate at the SPD. 
 

Secondly, MCB with its own micro-coil impedance element (e.g.: short-circuit protection of electromagnetic release), will increase the line when the lightning current through the residual pressure, causing the line overall residual pressure, elevate the risk of equipment insulation failure.