The correct answer is: D. generally on both sides of a circuit breaker.
An isolator is a device that is used to isolate an electrical circuit from the power supply. It is typically installed on both sides of a circuit breaker to provide a safe way to disconnect the circuit from the power supply for maintenance or repair.
Option A is incorrect because an isolator does not operate the relay of a circuit breaker. The relay is a device that is used to control the circuit breaker.
Option B is incorrect because an isolator is not a substitute for a circuit breaker. A circuit breaker is a device that is used to protect an electrical circuit from overloads and short circuits.
Option C is incorrect because an isolator is not always independent of the position of the circuit breaker. In some cases, the isolator may be installed in a different location than the circuit breaker.
I hope this helps! Let me know if you have any other questions.