What type of interlocking is used in a magnetic reversing starter to prevent energizing both coils at once?

• A. Electrical Interlock
• B. Mechanical Interlock
• C. Electrical and Mechanical Interlocking
• D. None

Answer: (C)

In a magnetic reversing starter, preventing both coils from energizing at the same time is essential to avoid a direct short or a high-stress condition on the motor. Achieving this reliability comes from using both mechanical and electrical interlocking. The mechanical interlock provides a physical barrier between the two contactors, so they cannot be closed simultaneously regardless of the control signals. The electrical interlock adds a control-circuit safeguard by ensuring that when one coil is energized, a normally closed contact in the opposite coil’s path opens or remains open, preventing the other coil from energizing. Using both methods together gives robust protection against both mechanical faults and control circuit faults, ensuring mutual exclusivity of the two directions. That’s why the best answer is electrical and mechanical interlocking.