Phoenix Contact 2277860 A window-type current transformer is a type of transformer used to measure electrical currents and voltages, designed for use in applications where space is limited, such as in utility meters or industrial monitoring systems, with an input primary current of 250 A AC and an output secondary current of 5 A AC, capable of accurately measuring up to 7.5 VA rated power while maintaining a high level of accuracy with an accuracy class of 1.