🔍 Key Concepts

• Autotransformer reduced-voltage starters – which contactors are used for starting vs running • The current path from L1–L2–L3 to the motor terminals T1–T2–T3 when the starter is in the run condition • How contactor R is mechanically interlocked with 1S and 2S, and what that implies about its function

💭 Think About

• On the diagram, imagine the motor has come up to speed and the circuit has shifted from start to run. Which contactors must now be de‑energized, and which one must be energized so the motor operates at normal line voltage? • Follow one phase, e.g., from L1 to T1. With R closed and the others in their run condition, do you see current flowing through the autotransformer windings, or is the autotransformer effectively bypassed? • Look at where the R main contacts are physically drawn in relation to the autotransformer taps and the motor leads. Are they tying the line to the transformer, the line to the motor, or the transformer to the motor during the run period?

✅ Before You Answer

• Verify which contactors (1S, 2S, R) are intended for starting/acceleration and which one for the run condition in an autotransformer starter. • Check whether, in the run condition, the autotransformer windings are still in series with the motor, or if they are completely bypassed. • Confirm what the R contacts actually connect together on the power diagram: line to motor, line to transformer, or transformer to motor.