It differs in actuation current.
Circuit breaker with B characteristic will be tripped immediately when a current flowing through it is equal to 3-5 times the rated current, that is in this case 96-160A.
On the other hand, the C characteristic is 5-10 times the rated current, i.e. about 160-320A, i.e. the circuit breaker will work at this current.
There is also a D (10-20x) characteristic, which is about 320-640 Amps.
The fuse characteristics are selected according to the type of load, and more precisely to the starting current.
Thus, B is used for domestic applications, because domestic appliances have low inrush currents.
But if we want to protect the motor (induction motors consume up to 8 times the rated current at start-up), then you have to use C, because the B motor will knock out at start-up. For example, a motor of about 10 kW, a three-phase motor consumes about 15A from the phase during normal operation, while at the start it consumes even 120A for a while.
Hope you understand now.
greetings
PS: For pre-meter protection (if that's what you mean when choosing), char is the best. C. Unless you have devices that will consume even more than 320 A at start-up, then D.
