A simple method to distinguish the neutral wire and the live wire of a multimeter
Generally speaking, to distinguish between neutral and live wires in a power supply, it is necessary to use a low voltage test pen. Can a multimeter be used to distinguish between live and neutral wires? The answer is affirmative, and the method is as follows:
Turn the range switch of the multimeter to the AC voltage range of 250V or 500V. Connect the black probe to a damp floor or ground in the indoor water pipe worker, and the red probe to the power cord or power socket hole. The multimeter indicates a high voltage value as the live wire, and a low or zero voltage value as the neutral wire
Place the multimeter in the AC voltage range of 250V. Connect one meter rod to the wire and the other to the wall or floor. If the wall or floor is particularly dry, use water to moisten it, which will have a more significant effect. If the multimeter pointer does not move, it indicates that the wire is neutral, and if the pointer deviates, it indicates that the wire is live. When we need to distinguish between live and neutral wires without a test pen in hand, we only need a multimeter to complete the test. There are three methods described as follows:
The first method: If you don't have a test pen and only have a multimeter, under normal voltage conditions, you can use the multimeter to distinguish between the live and neutral wires. Connect one probe of a multimeter to the live or neutral wire, and the other probe to the ground or a wall, metal water pipe, etc. If there is voltage (usually greater than 20V), it is the live wire; If there is no voltage, it is the neutral wire.
The second method: Firstly, we need to understand the principle of the test pen. The pen is composed of a metal rod, a neon bubble, a carbon resistor, and a metal cap. The neon bubble is a device that can emit light, a glass ball filled with inert gas, and the voltage of the carbon resistor is 1M ohms or more. The metal cap is the part that the human hand touches. When a person comes into contact with the metal cap, the live wire, the pen, the human body, and the earth form a circuit. There is a capacitance of about 100PF between the person and the earth, and the circuit is constructed in this way.
When measuring with a multimeter, whether it is a digital or pointer multimeter, after understanding the approximate range of the supply voltage, we take 220VAC voltage as an example and adjust the multimeter gear to 400VAC. Connect the red probe to the live or neutral wire and touch the black probe with your hand. If the multimeter shows a reading, it means it is a live wire; If there is no reading display, it is the zero line.
This method does not pose any danger to the human body because the internal resistance of a digital multimeter is 10M ohms, and the internal resistance of a pointer meter is 20K ohms/V. If measuring a voltage of 220V, the internal resistance of the pointer meter is 20K × 220V=4400 ohms, which is absolutely safe because the carbon resistance of an electric pen is generally 1M ohms.
