Costing running 3 phase motors

[mickfred]

Been asked to cost the running a number of motors . Was going two amp test each phase and multiple by line neutral voltage to get kWh . Is this correct .ta

 

[Lucien Nunes]

Not quite. Multiplying current by voltage will give you the input kVA, not kW, because the two separate readings don't take into account the phase angle. It would be correct for a heating element but not for a motor, the figure will be too high by the power factor. Heavily loaded motors will be reasonably close, lightly loaded ones will give you a pessimistic figure. The only way to get the exact power that you pay for is to use a proper wattmeter.