Question 182Electricity & Electronics - 1st Asst/Chief

The correct answer is D) an open auxiliary "M" contact. When the start button is pushed, it energizes the "M" contactor coil, which then closes the main motor contacts to start the motor. However, when the start button is released, the auxiliary "M" contact is responsible for keeping the "M" contactor coil energized, allowing the motor to continue running. If this auxiliary "M" contact is open, the "M" contactor coil will de-energize as soon as the start button is released, causing the motor to stop. The other options are incorrect because an open in the stop button contact (A) would not allow the motor to start at all, an open "M" contactor coil (B) would prevent the motor from starting, and a corroded contact on the disconnect switch (C) would not specifically cause the motor to stop when the start button is released.