What is the function of an overload relay in an electrical motor circuit?

The function of an overload relay in an electrical motor circuit is primarily to protect against overheating. When a motor operates under excessive current conditions—typically caused by a mechanical overload, a jam, or other factors—the overload relay monitors the current flowing through the motor. If the relay senses that the current exceeds a predetermined threshold for an extended period, it will open the circuit, thus disconnecting power to the motor. This action helps prevent damage to the motor's windings due to excessive heat, which can lead to insulation failure and ultimately motor burnout.

While overload relays can contribute to circuit safety, they are specifically designed to address conditions that lead to motor overheating rather than prevent short circuits, limit current, or detect phase failure. Each of those functions typically falls under the responsibilities of other protective devices in an electrical system, such as circuit breakers for short circuits or phase failure relays for detecting phase imbalances.