What type of fault does a thermal overload relay protect against?

A thermal overload relay is designed to protect electrical motors from prolonged overload conditions that can result in overheating. This type of fault occurs when a motor draws more current than its rated capacity for an extended period, often due to excessive load or mechanical issues. The thermal overload relay monitors the current flowing to the motor and operates based on the heat generated by this current.

When the current exceeds a predetermined level for a certain duration, the relay opens the circuit, cutting off power to the motor. This action prevents damage that could occur due to excessive heat, which can result in insulation failure, bearing damage, or even motor burnout.

Thermal overload relays are not effective against other types of faults such as ground faults, which occur when there is an unintended path to ground, or short circuits, which involve a direct connection allowing high current to flow in an unintended manner. Additionally, while they may help in situations where a phase loss might lead to imbalances, their primary function is specifically to detect and respond to prolonged overload conditions.