Which device is typically used to provide isolation between the control signal and the high-power motor circuit?

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

Answer: (B)

Isolation between the control signal and the high-power motor circuit is achieved with a device that has a low‑voltage control coil and separate high‑current contacts. A contactor fits this role perfectly because it is designed to be energized by the control circuit and to switch the motor’s power path. When the control coil is energized, the contacts close and feed power to the motor; when the coil is deenergized, the contacts open, effectively isolating the motor from the control side. This arrangement provides galvanic separation and keeps motor surges and faults away from the control electronics, while offering the durability and current rating needed for motor applications. A switch is manual, not suitable for automated control; a fuse provides protection but does not offer controllable isolation during normal operation; a relay can provide isolation but is typically used for lower power, whereas a contactor is the standard choice for high‑power motor control due to its higher current rating and robustness.