A simplified circuit diagram of the two-wattmeter connections is shown in Fig.1. Figure1
is simplified in the sense that the ammeters, current transformers, selection switch, and
polarity switch have been omitted. The polarities of the voltage and current connections
to the wattmeters are significant. Note that the line in which the current is not measured,
line “c”, is connected to the negative voltage terminal on both wattmeters.