Final answer:
An instantaneous circuit breaker reacts to a short circuit by opening the circuit instantly to protect the circuit and prevent any damage or overheating.
Step-by-step explanation:
An instantaneous circuit breaker reacts to a short circuit by opening the circuit instantly. It is designed to quickly interrupt the flow of current in the event of a short circuit to protect the circuit and prevent any damage or overheating. In comparison to other circuit protection devices like fuses, circuit breakers offer the advantage of being resettable, allowing the circuit to be restored after the short circuit is resolved.