An application engineer needs all of the facts to make an intelligent choice of an overcurrent protection device for a particular application.

The following link is to an article that suggests a seven step procedure that may be followed when selecting an overcurrent supplementary protector, circuit breaker or fuse.

http://www.mechprod.com/overcurrent-protection-selection/

The first six steps in this procedure define the problem in a detailed engineering sense. Then the seventh step, the actual choice of a particular overcurrent protector, can be made from a logical and relevant knowledge base.