By measuring the current ,and come to the conclution is not the correct answer,for example We take oneHP/4pole/ motor,it takes approximately8 amps in idle run,2pole motor takes4 amps,6pole motor takes amps,where as8pole motor takes nearly to amps as idle load,then how can we come to the conclution only taking the idle current only.So first we should measure the resitance at degree centigrade,then check the rpm of the motor by given the3 ph. supply,take the frame dimension,winding wire gauge size,This the way to know the details of No name plate motors to know the HP