A thermal overload relay monitors current; if current exceeds rating due to overload, it trips the circuit; resets after cooling.

Prepare for the NCCER Electrical Level 2 Control Systems and Fundamental Concepts exam. Utilize flashcards and multiple choice questions with hints and explanations. Ensure success on your exam!

The main idea is protective control that uses heat from current to act. A thermal overload relay protects a motor by using a bimetallic element that is heated by the motor current. When current stays within the rated level, the element stays flexible and allows normal operation. If the current exceeds the rating due to overload, enough heat builds up to bend the strip and open the contacts, tripping the circuit to stop the motor. After the motor has cooled and the element returns to its normal state, the relay resets and the motor can be restarted. This behavior matches the description of monitoring current, tripping on overload, and resetting after cooling. The other options don’t fit because the device doesn’t measure coil temperature directly, doesn’t automatically reduce current as a regulator, and doesn’t create a short circuit.