🔍 Key Concepts

• Trace the current path from the 3-phase supply (L1, L2, L3) through the contactors (KM1, KM2, KM3) to the motor, noting where the OL (overload) device is located. • Distinguish between overload protection (responds to sustained overcurrent) and short-circuit/fault protection (fast-acting fuses). • Look at how the OL contact symbol appears in the control circuit side and how it would interrupt the coil of the main contactor feeding the motor.

💭 Think About

• Follow the diagram and ask: when the motor draws too much current for a long time, which device is designed to heat up and then open a control contact, rather than simply blowing a fuse? • Which component, when it operates, will cause the main contactor feeding the motor to drop out, thereby disconnecting the motor from the line? • Are the listed fuses primarily sized and placed for line/transformer protection, or for sensing sustained overload in the motor windings themselves?

✅ Before You Answer

• Verify which symbol in the power circuit is labeled OL and how its contacts are shown in the control circuit (normally closed contact in series with the contactor coil). • Check which devices (by label) are directly in series with the motor line conductors versus those that only protect the control transformer or incoming line. • Confirm which device is explicitly associated with overload relay heaters rather than just short-circuit protection fuses.