What is the purpose of overload relays in motor control circuits?

Overload relays serve a critical function in motor control circuits by protecting the motor from overheating, which can occur due to excessive current. When a motor operates under high load conditions, it draws more current than its rated value. This excess current can lead to increased heat within the motor, potentially causing windings to fail or insulation to break down, resulting in permanent damage.

Overload relays are designed to detect this abnormal current situation. They monitor the current flowing to the motor; if it exceeds a predetermined threshold for a certain time, the relay will trip, interrupting the power supply to the motor. This action effectively prevents damage by stopping the motor before it overheats, ensuring a longer service life and reliability of the motor system.

In contrast, the other options incorrectly attribute functions to the overload relay that do not align with its purpose in motor protection. Enhancing torque output or increasing motor speed pertains to other types of circuitry or devices, while controlling the direction of motor rotation would typically be managed by a contactor or another control mechanism rather than an overload relay.