What is the correct method to obtain a control voltage of 120 VAC from a dual-voltage control transformer when the line voltage is 480 VAC?

To obtain a control voltage of 120 VAC from a dual-voltage control transformer when the line voltage is 480 VAC, connecting the primaries in series is the correct method. In a dual-voltage transformer, each primary winding is designed to handle a specific voltage, typically allowing for different configurations depending on the supply voltage available.

When the transformer is designed with dual primary windings, they can be configured for different voltages by connecting them appropriately. In this case, connecting the primaries in series effectively doubles the voltage supplied to each winding, which can match the higher line voltage of 480 VAC when using both windings. This configuration allows for proper voltage handling and ensures that the transformer operates within its designed parameters.

By contrast, other methods may lead to incorrect voltage outputs or unsafe operating conditions. Attempting to connect the primaries in parallel would not yield the desired output voltage and might cause an imbalance or overcurrent situation. Using only one primary winding would reduce the available voltage and not meet the requirement of achieving 120 VAC from 480 VAC. Stating that it is impossible to obtain 120 VAC this way ignores the capabilities of a dual-voltage transformer when used correctly. Thus, connecting the primaries in series is the appropriate and effective