Physics joke zero line fire line

Ruh distinguishes the zero line and the zero line of the live wire as follows:

1, power on, measure with an electric pen, and all lights will be on.

2. Disconnect the zero line at the main switch, only connect the fire line, turn on the lights at home, and measure with an electric pen. It didn't light up just now. Now the lights are all zero lines, and the rest are all ground lines.

3. After determining the live wire with an electric pen, connect two bare wires and live wire to the 220V bulb respectively, so that the zero wire and the ground wire can be distinguished from each other in brightness. The light is the zero line, and the dark is the ground line.

The colors are as follows: Generally speaking, the three wires are live wire, zero wire and ground wire; The fire line is generally red, yellow and green; The zero line is generally blue and black; The grounding wire is usually bicolor. In addition to distinguishing colors, you can also measure with a universal electric pen. First, measure directly with an electric pen. All lights are live wires for the first time, then disconnect the zero line at the main switch, and then measure with an electric pen. What didn't light up before was the zero line, and the rest was the ground line.