A technician is troubleshooting a motor control circuit where a 3-phase induction motor fails to start. The control circuit uses a 24 V AC control supply, a normally open (N.O.) start button, a normally closed (N.C.) stop button, and a contactor coil (CR-1). When the start button is pressed, the contactor energizes, but the motor de-energizes immediately upon releasing the start button. What is the most likely cause?

Question: A technician is troubleshooting a motor control circuit where a 3-phase induction motor fails to start. The control circuit uses a 24 V AC control supply, a normally open (N.O.) start button, a normally closed (N.C.) stop button, and a contactor coil (CR-1). When the start button is pressed, the contactor energizes, but the motor de-energizes immediately upon releasing the start button. What is the most likely cause?

Answer options: ✅ The holding contact for CR-1 is faulty or miswired.

• The stop button is wired incorrectly (N.O. instead of N.C.).
• The overload relay contacts are open.
• The motor's thermal protectors have tripped.

Correct answer: The holding contact for CR-1 is faulty or miswired.

Explanation: If the contactor energizes when the start button is pressed but de-energizes upon release, it indicates that the holding circuit (also known as the seal-in or latching circuit) for the contactor is not maintaining the coil's energization. This holding circuit typically involves a N.O. auxiliary contact of the contactor wired in parallel with the start button.