Isolator is a mechanical switch which isolates a part of circuit from system as when required. Electrical isolators separate a part of the system from the rest for safe maintenance works. Circuit breaker always trip the circuit but open contacts of breaker cannot be visible physically from outside of the breaker and that is why it is recommended not to touch any electrical circuit just by switching off the circuit breaker. So for better safety there must be some arrangement so that one can see open condition of the section of the circuit before touching it.