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9.3. One Wattmeter Method

In this method the current coil is connected in anyone line and the pressure coil is connected alternately between this and the other two lines as shown in Fig. 33. The two readings so obtained, for a balanced load, correspond to those obtained by normal two wattmeter method.

This method is not of as much universal application as the two wattmeter method because it is restricted to fairly balanced loads only. However, it may be conveniently applied, for instance, when it is desired to find the power input to a factory motor in order to check the load upon the motor.