🔍 Key Concepts
• Review how an autotransformer reduced-voltage starter works, especially the sequence of contactors (1S, 2S, and R).
• Look at where the 1S contacts are physically located in the power circuit (bottom of the diagram) and which transformer taps (0%, 50%, 65%, 80%, 100%) they connect to.
• Compare the function of 1S in the control circuit (top) with its function in the power circuit (bottom) to understand what it actually does in the starting sequence.
💭 Think About
• Trace the current path from L1/L2/L3 through 2S, the autotransformer, and then through 1S to the motor: at what point in the starting sequence does 1S energize the motor and how?
• Ask yourself: does 1S ever connect the motor directly across the line, or does it only connect the motor to a particular tap of the autotransformer?
• Consider which contactor would logically be used for the very first application of voltage to the motor versus any subsequent speed or connection changes.
✅ Before You Answer
• Verify which contactor (1S, 2S, or R) is in series with the 0% tap (full autotransformer output) going to the motor leads T1–T3.
• Confirm whether 1S is used when the motor is first energized at reduced voltage (first step) or when changing from reduced‑voltage to full‑voltage operation.
• Check the labels near the taps (0%, 50%, 65%, 80%, 100%) and see which tap the 1S power contacts actually make use of. This will tell you the correct functional name.