The actual electrical power consumption (effective power) of a load of an electrical apparatus or others is given by a product between the apparent power and the power factor. 
To obtain a power factor, the information of a phase difference between a voltage and a current is required. 
For this reason, when obtaining for the effective power, measuring by connecting the terminal of a measuring apparatus to an conductor wire of an electrical cable directly is commonly done. 
Related reference is as follows:    Japanese Laid-open Patent Publication No.  2001-255342;    Japanese Patent No.  4251961; and    Japanese Laid-open Patent Publication No.  Hei 11-133065.