In a bimetallic overload relay, what causes the bimetallic strip to spring away and open the motor control circuit when current exceeds rating?

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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!

Multiple Choice

In a bimetallic overload relay, what causes the bimetallic strip to spring away and open the motor control circuit when current exceeds rating?

Explanation:
Heat from the current heats the bimetallic strip. The strip is made of two metals with different coefficients of thermal expansion, so as it heats, one metal expands more than the other and the strip bends. This bending trips the mechanism and opens the motor control circuit to protect the motor. Light, sound, or magnetic effects aren’t what cause the strip to move in this type of relay.

Heat from the current heats the bimetallic strip. The strip is made of two metals with different coefficients of thermal expansion, so as it heats, one metal expands more than the other and the strip bends. This bending trips the mechanism and opens the motor control circuit to protect the motor. Light, sound, or magnetic effects aren’t what cause the strip to move in this type of relay.

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