🔍 Key Concepts

• Difference between overload protection and short-circuit protection in motor circuits • Which components in the diagram are in the power (motor) branch circuit versus in the control circuit • How fuses and thermal overload relays (OL) each respond to excessive current

💭 Think About

• Trace the path of heavy motor current from L1, L2, and L3 to the motor terminals. Which protective devices does this current actually pass through? • For a sudden bolted short at the motor terminals, which device must act almost instantaneously, and which device is designed to respond more slowly to moderate overcurrent? • Look at FU4–FU7 and the fuses in Q1: which ones are clearly on the control transformer or control wiring, and which are sized to interrupt high fault current in the motor branch?

✅ Before You Answer

• Be clear on what is meant by motor branch circuit (the main power conductors feeding the motor, not the low‑power control wiring). • Identify which fuses are on the control circuit versus the power circuit in the illustration. • Confirm which device is specifically designed for short-circuit / ground-fault protection rather than for overload protection.