Which of the following is a characteristic of thermal overload relays?

Thermal overload relays operate based on the principle of resistive heating. When current flows through the relay, it generates heat due to the electrical resistance of the conductor. This heating effect is utilized to measure the temperature rise in the relay, which corresponds to the current flowing through it. If the current exceeds a certain threshold for an extended period, the heat generated can cause the relay to trip, disconnecting the motor from the power supply and thus preventing damage from overheating.

This characteristic makes thermal overload relays essential for protecting motors from overload conditions, as they inherently account for the prolonged heat buildup rather than instantaneous changes in current. This prevents nuisance tripping during brief current spikes that might occur during normal operational fluctuations or startup conditions.