A _________________ belongs to both the control circuit and the power circuit.

• A. Switch
• B. Contactor
• C. Controller
• D. Relay

Answer: (B)

A device that has a control-side coil and power-side contacts is meant to bridge the control and the power circuits, letting a low-energy control signal switch a high-current load. The cont actor is exactly that: its coil sits in the control circuit and, when energized, pulls in the heavy-duty contacts that switch the power circuit. This setup keeps the control signal isolated from the high-power path while enabling remote or automatic operation of motors and other large loads.

The other options don’t fit as well. A switch is typically manually operated and sits directly in the power path without a separate control coil. A controller provides logic but doesn’t itself handle the power switching. A relay also uses a coil and contacts, but it is usually used for smaller loads and signaling rather than the heavy-duty switching common in motor control.