Question

How many contactors does a star-delta motor starter require?

• A. Two
• B. Three
• C. Four
• D. Five

Answer 1

The Correct Option is B

A star-delta starter is a type of reduced voltage starter for induction motors. It reduces the starting current of the motor by initially connecting it in a star (Y) configuration and then, after a set period, switching it to a delta (Δ) configuration for normal operation.
To implement this control, the starter requires the following three contactors:

Main Contactor (KM1) – Connects power to the motor circuit.
Star Contactor (KM2) – Connects motor windings in star during startup.
Delta Contactor (KM3) – Connects motor windings in delta after transition.
These contactors work in coordination through a timer to switch between star and delta connections safely and effectively.