š Key Concepts
ā¢ Review how an autotransformer reduced-voltage starter works, especially the sequence of contactors (1S, 2S, and R).
ā¢ 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.
ā¢ 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.
š Think About
ā¢ 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?
ā¢ 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?
ā¢ Consider which contactor would logically be used for the very first application of voltage to the motor versus any subsequent speed or connection changes.
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Before You Answer
ā¢ Verify which contactor (1S, 2S, or R) is in series with the 0% tap (full autotransformer output) going to the motor leads T1āT3.
ā¢ Confirm whether 1S is used when the motor is first energized at reduced voltage (first step) or when changing from reducedāvoltage to fullāvoltage operation.
ā¢ 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.