The contactor sequence for the circuit entails the energized contactors being 2S and _____ during the transition from reduced-voltage operation to full-voltage operation.

In a reduced-voltage to full-voltage transition for motor control circuits, the operation of contactors is critical to manage the phases of starting and running the motor safely and efficiently. The sequence typically involves a two-stage process where starting occurs at a lower voltage to limit the inrush current, and then the motor is shifted to full voltage for normal operation.

In this context, the correct answer involves identifying which contactor, along with 2S, is energized during the transition period. When operating under reduced voltage, contactor 2S is primarily responsible for engaging the reduced-voltage configuration. As the system transitions to full voltage, it is common practice to engage contactor 1S to complete the circuit and take over the load.

By understanding the role of each contactor in this sequence, we can see why 1S is the correct choice. It signifies that 2S and 1S work together during the crucial phase where the system smoothly shifts from one operational state to the next. In practical applications, this arrangement prevents abrupt changes that could lead to electrical stress or mechanical failure in the motor and associated components.