First of all, household electricity, generally three-phase electricity, is also a line of three colors, each color has a commonly known connection method, although sometimes reversed can also be used, but later problems have affected the maintenance.
According to the “Code for Construction of Residential Decoration Engineering” GB 50327-2001 16.1.4: When wiring, the color of the phase line and the neutral line should be different; the color of the same residential phase line (L) should be uniform, the zero line (N) Blue should be used, and the protective wire (PE) must be yellow-green two-color.
The phase line is also the fire line we are talking about. Usually, red, yellow and green are used as the fire line, blue is the zero line, and the ground line is the protection line mentioned above is usually the two-color line.
Because the wire color is more, but in general, if you encounter a red line, it must be a fire line. In a single-phase lighting circuit, generally yellow indicates a live line, blue is a neutral line, and yellow-green is a ground line.