To make the basic single-phase transformer move versatile, both the primary and secondary windings can be made in two equal parts. The two parts can be reconnected either in a series or in parallel . This provides added versatility as the primary winding can be connected for either 480 volts or 240 volts and the secondary winding can likewise be divided into two equal parts providing either 120 or 240 volts. (note: there will be four leads per winding brought out to the terminal compartment rather than two). Either arrangement will not affect the capacity of the transformer. Secondary windings are rated with a slant such as 120/240 and can be connected in a series for 240V or in a parallel for 120V or 240/120V (for 3-wire operation). Primary windings rated with an "X" such as 240X480 can operate in series or parallel but are not designed for 3-wire operation. A transformer rated240X480V primary, 120/240V secondary could be operated in 6 different voltage combinations.

Primary in series, secondary in series.
Primary in series, secondary in series. (3 wire operation)

Primary in series, secondary in parallel.
Primary in parallel, secondary in series.

Primary in parallel, secondary in series.
Primary in parallel, secondary in parallel.