Generally, the secondary circuit of low-voltage electric control cabinet has a minimum wiring cross-sectional area of 1.5 square meters for voltage circuits and a minimum cross-sectional area of 2.5 square meters for current loops. Current loops refer to current transformers, ammeters, current signal lines of power factor meters, current signal lines of mutual inductance watt-hour meters, etc. The current flowing through is 5 amperes. In addition, the power line is yellow, green, and red, and the neutral line is blue or light blue (some are gray. Because international standards also distinguish between European standards and American standards). The main circuit line is at least 1.5 square millimeters of black wire, the control line is 1.0 square red wire for AC voltage, and 1.0 square blue wire for DC voltage. There is no requirement for the color of the signal line.