Explain a star-delta (Y-Δ) starter and its benefit.

• A. Start in delta, then star for running; reduces inrush current.
• B. The star-delta starter uses a direct-on-line method to reduce torque.
• C. Start in delta and remain delta; no inrush reduction.
• D. Initially connect the motor in star to reduce voltage during start, then switch to delta for running; this reduces inrush current and electrical stress.

Answer: (D)

The idea being tested is using a star-delta starting method to limit stress during motor start. At start, the windings are connected in star, so each winding sees about the line voltage divided by √3. This reduces the voltage per winding, which in turn lowers the starting current and the torque produced at start—roughly about one-third of what a direct-on-line start would draw. Once the motor reaches a sufficient speed, the wiring is switched to delta for normal running, where each winding sees the full line voltage and the motor delivers full torque. This approach cuts inrush current and electrical stress on the supply and motor, helping prevent voltage dips and nuisance tripping while still providing full torque once running. The other options either start with full voltage (no inrush reduction) or keep the windings in a configuration that doesn’t reduce startup current.