The correct answer is: C. Load break switch.
A load break switch is a device used to isolate an electrical circuit from a power source. It is not designed to interrupt current, and therefore does not require a current rating.
A circuit breaker is a device that is designed to interrupt current. It is used to protect electrical circuits from overloads and short circuits. Circuit breakers are typically rated for a specific current, and must be selected to match the current carrying capacity of the circuit they are protecting.
An isolator is a device that is used to disconnect an electrical circuit from a power source. It is not designed to interrupt current, and therefore does not require a current rating. Isolators are typically used to isolate equipment for maintenance or repair.
Circuit breakers and load break switches are both devices that are used to isolate electrical circuits from a power source. However, circuit breakers are designed to interrupt current, while load break switches are not. Therefore, the current rating is only necessary for circuit breakers.