If one is going to guesstimate how much load they are going to use at one time - it is important that the feeder overcurrent protective device be sized accordingly.
So, if one estimates their load will be no more that 50A and one sizes the wire for 50A - then one must install a breaker rated 50A.
The Feeder OCPD limits the load.
A conductor sized for 50A must not be connected to a breaker rated 100A (in general). The breaker will pass 100A. It cares not wither or not the conductors are rated for.
