Which device is commonly used to switch a motor's power circuit in an electrical control system?

• A. Contactor
• B. Relay
• C. Fuse
• D. Transformer

Answer: (A)

Switching a motor’s power requires a device that can handle high current and withstand repeated on/off operation. A contactor is designed for this exact purpose: it’s a heavy‑duty electromagnetic switch whose power contacts close to connect the motor to the supply when the control coil is energized. The control circuit only needs a small current to operate the coil, while the motor current flows through the contactor’s main contacts. Often, a protective device like an overload relay is used in the same control circuit to guard the motor from overheating or damage.

Relays serve a similar purpose but are typically rated for much smaller loads, so they aren’t ideal for directly switching a motor. A fuse protects circuits by interrupting current in a fault, but it doesn’t function as a switch in normal operation. A transformer changes voltage levels, not the motor’s power switch.