Which type of overload device uses a coil to sense motor current?

The correct type of overload device that uses a coil to sense motor current is the magnetic overload. This device operates based on the principle that when motor current exceeds a predetermined level, the magnetic field generated by the coil becomes strong enough to trip the mechanism and interrupt the current.

The design typically involves a coil wound onto a magnetic core. As the motor draws current, it creates a magnetic field in the coil. If the current reaches a level that could cause damage or overheating, the resultant magnetic force can actuate a switch or relay, effectively protecting the motor from excessive current flow.

In contrast, thermal overload devices rely on temperature changes caused by current flowing through a heating element, while bimetallic overload devices use a bimetallic strip that bends with heat generated from the current. Electronic overload devices monitor current via sensors and use electronic circuitry to provide overload protection. Each of these devices operates using different principles, reinforcing why magnetic overload is the correct answer in this context.