Methods used to measure the power factor in low-voltage test circuits are covered. Since the power factor measurement for high-capacity test circuits is particularly difficult, and different methods may yield different results, the methods that are least likely to yield errors are recommended for particular circuit conditions. The ratio method is recommended for fast clearing devices that may have total interruption times of 0.5 cycle or less. The DC decrement method is recommended for circuits with a 30% power factor or less when the device to be tested interrupts at a point in time more than 0.5 cycle from the initiation of the current. The phase relationship method, using current and voltage waves, is recommended for circuits having power factors over 30%.

This standard describes three methods used to measure the power factor in 60 Hz inductive low-voltage (1000 volts and below) test circuits. Similar methods may apply at other frequencies. These methods are: 1) Ratio method; 2) dc decrement method; 3) Phase relationship method; These preferred methods are shown in Table 1.

The purpose of this standard is to recommend methods of measuring power factor for inductive test circuits by such means as oscillographic records, so that the preferred method, giving the greatest accuracy, is recommended for any particular circuit.