Through the distribution transformer operation da.ta, equipment data, the situation of consumer expanding that powersupply company masters, the maximum low.voltage range is judged,which helps the company determine the possible areas of low.volt.age happening and analyze the reasons of three.phase imbalance byimbalanced loads.This paper provides the calculation method ofequivalent current unbalance degree before installing.By the chang.es of current imbalance value and low.voltage consumers’range,the junctions is determined whether is reasonable to avoid the occur.rence of low.voltage because of the human factors before junction.