I had a lab session where I did the two watt metre test on a 3 phase, 4 wire star system. I have values for each line voltage and line current. I also have a total power measurement. Should the total power be equal to the sum of each line voltage multiplied by their respective currents? When I do this the power works out about 0.6kW larger then the total power reading I read off. I was wondering whether you need to take phase angles and all that stuff into consideration?