In diagnosing a control circuit with multiple relays, why is it important to verify coil energization before testing contacts?

• A. To confirm the power supply is active
• B. To ensure the coil is receiving the control signal
• C. To measure coil resistance
• D. To identify mechanical wear

Answer: (B)

The main idea is to confirm that the relay coil is actually being commanded to operate. When diagnosing a control circuit with multiple relays, you can only test the contacts meaningfully after you know the coil is energized, because the contacts only change state when the coil is energized. Verifying energization isolates the control path from the contact path, so you can determine whether any issue is in the control signal or the contacts themselves. If the coil isn’t energizing, testing the contacts would be misleading since their state depends on the coil; you’d be chasing a control-signal problem rather than a contact problem. A power supply being active is related, but it doesn’t confirm that the control signal is actually reaching and energizing the coil. Measuring coil resistance is a separate check, and identifying mechanical wear isn’t determined by energizing the coil.