What is the function of the melting alloy in bimetallic overload relays?

• A. To create a stronger magnetic field
• B. To approximate the heat generated in the motor
• C. To decrease trip response time
• D. To enhance the structural integrity of the relay

Answer: (B)

The function of the melting alloy in bimetallic overload relays is to approximate the heat generated in the motor. This is essential in overload protection because as the motor operates, it generates heat due to electrical current flowing through it. The bimetallic strip within the relay responds to this heat; when the temperature reaches a certain threshold—corresponding to an overload condition—the melting alloy will soften or melt. This action causes the mechanism to trip, thereby disconnecting the power to the motor and preventing potential damage from overheating.

The choice of using a melting alloy is particularly effective because it allows for a very precise response to the specific temperature generated by the motor under excessive load. This ensures that the relay will disconnect the motor at the appropriate time to prevent damage, mimicking the thermal effects that would naturally occur in the motor itself under overload conditions.