What connection type would allow a transformer's secondary windings rated 120/240 to deliver 240 volts?

The connection type that allows a transformer's secondary windings rated 120/240 volts to deliver 240 volts is a series connection.

In a series connection, the voltage across the windings can be summed, meaning that if one winding is rated at 120 volts and the other at 120 volts as well, when connected in series, the total voltage available would be 240 volts. This configuration utilizes both windings effectively to achieve the higher voltage output.

This concept is fundamental in transformer operation, where the output voltage is dependent on how the windings are interconnected. A parallel connection would not increase the voltage; instead, it would provide the same voltage rating as one of the windings while sharing the current load. Single and double connections do not pertain to the standard terminology used for transformer winding configurations.