🔍 Key Concepts

• Motor starter control circuit: how the Stop, Start, and M coil work together in the lower (B) diagram • What a loud hum without rotation usually indicates about the motor (stalled / locked rotor, high current) • Why we use overload protection (OL) and the importance of de‑energizing a circuit before troubleshooting

💭 Think About

• When the motor is humming but not turning, what does that tell you about whether the M contactor coil is currently energized? Trace the circuit in diagram B from L1 through Stop/Start to the M coil. • Before you touch or inspect any part of a stalled motor or its starter, what must you do with the control circuit to remove power from the motor and the M contactor? • Under what condition would the thermal overload (OL) need to be reset, and does the diagram or the question say that this condition has already occurred?

✅ Before You Answer

• Verify which device in the control circuit actually removes power from the M coil and opens the main contacts feeding the motor. • Confirm whether the overload contacts (OL) would already be tripped just because the motor hums briefly, or if they trip only after sustained overcurrent. • Eliminate any option that involves working on or holding energized components (like the contactor or internal motor parts) before the circuit is safely de‑energized.