The live wire is the phase wire, which is equivalent to the positive level of direct current. The industry standard is to use yellow, green and red to represent ABC three-phase live wire. The zero line is equivalent to the negative pole of direct current, usually represented by blue and black, and is represented by the word "n". However, there is no difference between positive and negative alternating current, and the current starts from the live wire, flows through the electrical equipment and then flows back to the neutral point of the transformer through the zero line to complete the loop.

Method 2, induction method, this method is only applicable to those without ground wire, and if there is ground wire, it should be operated according to method 1.