Final answer:
The correct answer to the question is a contactor, which is a device specifically designed to switch a large amount of electrical power through its contacts.
Step-by-step explanation:
A system control that loads by opening and closing electrically operated mechanical switches is best described as a contactor. A circuit breaker and a fuse act like automatic switches that open when sustained current exceeds desired limits, typically for safety reasons to prevent thermal hazards. A regular switch, such as a light switch, is a device that opens and closes to control the flow of electricity but does not operate automatically. Finally, a relay is a type of switch that is operated electrically; however, it is typically used to control a high-power circuit with a low-power signal. Considering the description of the system control, a contactor is the most accurate answer as it is designed to control electric motors and other high-power loads with an electromechanical mechanism.