In a bimetallic overload relay, what physical change causes the strip to trip when overheated?

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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 physical change causes the strip to trip when overheated?

Explanation:
The key idea is thermal actuation from a bimetal strip. Two metals with different coefficients of thermal expansion are bonded together. When overheated, they expand by different amounts, causing the strip to bend. That bend moves a mechanical linkage and opens the contacts, which trips the overload relay. This mechanism relies on the differential expansion, not on melting fuses, coil expansion, or magnet-core changes. The other options describe other protection mechanisms, not how a bimetallic overload relay senses and trips on heat.

The key idea is thermal actuation from a bimetal strip. Two metals with different coefficients of thermal expansion are bonded together. When overheated, they expand by different amounts, causing the strip to bend. That bend moves a mechanical linkage and opens the contacts, which trips the overload relay. This mechanism relies on the differential expansion, not on melting fuses, coil expansion, or magnet-core changes. The other options describe other protection mechanisms, not how a bimetallic overload relay senses and trips on heat.

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