NEIEP Mechanics Practice Exam

What is the primary reason AC relay hum or chatter occurs?

1. Faulty power supply

2. AC cycle reversal

3. Overheating components

4. High load conditions

The correct answer is: AC cycle reversal

AC relay hum or chatter primarily occurs due to AC cycle reversal, which is a situation where the alternating current does not reach a stable point within the electrical cycle, leading to rapid fluctuations in the magnetic field of the relay. This continual fluctuation can cause the armature of the relay to vibrate or rattle, resulting in what is known as hum or chatter. Understanding this phenomenon requires knowledge of how AC relays operate. In a stable condition, the relay's armature is held firmly in either the open or closed position by the magnetic field created by the AC voltage. However, when there is a cycle reversal, the magnetic forces may become inconsistent or insufficient to maintain a continuous hold on the armature, causing it to oscillate. The other listed options do not typically lead to the hum or chatter phenomenon. A faulty power supply may lead to malfunctioning equipment but is not specific to the behavior of the relay’s operation in terms of magnetic field stability. Overheating components can affect relay function and lifespan, yet they do not inherently cause the humming sound associated with AC relay chatter. High load conditions might influence relay performance, but they do not directly correlate with the cyclical disruptions that lead to the noise. Overall, the mechanical