A simple way to distinguish between zero and live wires with a multimeter
Generally speaking, to identify the neutral wire and the live wire in the mains, you must use a low-voltage test pen. Can you use a multimeter to distinguish the live wire and the neutral wire? The answer is yes, and the method is as follows:
Turn the range switch of the multimeter to the AC voltage 250V or 500V range. The black test lead is connected to the plumber in the room, the wet ground, land, etc., and the red test lead is in contact with the power line or the power socket hole. The higher voltage value indicated by the multimeter is the live wire. The voltage value is low or zero is the zero line.
Put the gear of the multimeter on the AC voltage 250V gear, connect one meter stick to the wire, and the other one is in contact with the wall or the ground, (if the wall or the ground is particularly dry, you can use water to make it wet, so the effect is more significant) If the pointer does not move, it means that this line is the zero line, and if the pointer deflects, it means that this line is the live line. When we want to distinguish live wire and neutral wire without a test pen in hand, we only need a multimeter to complete the test. There are three methods as follows:
The first method: If you don’t have a test lead and only a multimeter, you can use the multimeter to distinguish the live wire and the neutral wire when the voltage is normal. Use one test lead of the multimeter to connect the live wire or the neutral wire, and the other test lead to ground or the wall, metal water pipe, etc. If there is voltage (generally greater than 20V), it is the live wire; if there is no voltage, it is the neutral wire.
The second method: First of all, we need to understand the principle of the electric pen. The electric pen is composed of a metal rod, a neon bulb, a carbon resistor, and a metal cap. The neon bulb is a device that can emit light. A glass ball filled with an inert gas, carbon The voltage of the resistor is 1M ohms or above, and the metal cap is the part that the human hand touches. When the person touches the metal cap, the live wire, the electric pen, the human body and the earth form a loop, and there is a capacitance of about 100PF between the person and the earth, and the loop is Constructed like this.
When we use a multimeter to measure, regardless of whether it is a digital or an analog multimeter, after understanding the approximate range of the power supply voltage, we take 220VAC voltage as an example, adjust the gear of the multimeter to 400VAC, and connect the red test lead to the live wire or the neutral wire. When the hand touches the black test lead, if the multimeter has a reading display at this time, it means that it is the live wire; if there is no reading display, it is the zero line.
This method will not cause any danger to the human body. The reason is that the internal resistance of the digital multimeter is 10M ohms, and the internal resistance of the pointer meter is 20K ohms/V. If the measured voltage is 220V, the internal resistance of the pointer meter is 20K × 220V = 4400 ohms, which is absolutely safe. , because the internal resistance of the carbon resistance of the electric pen is generally 1M ohm.
