Using a multimeter to identify zero wire and fire wire
The easiest and most direct way to tell the difference between a zero wire and a fire wire is to use an electric tester to test it. As an electrician's eyes, the pen is not only easy to operate, but also safe and reliable. In the absence of a power test pen, we can also use a multimeter to distinguish between the zero line and the fire line, the specific operation method is as follows:
Single pen test method
Dial the dial of the pointer multimeter (digital meter) to the position of AC voltage 500V. Hold the insulated part of the end of the red pen in your right hand, and put the metal tip of the pen against the wire under test; pinch the metal tip of the black pen with the fingers of your left hand. If the meter needle shows a voltage (the size of the voltage is related to the degree of dryness of the skin, shoes, etc.), it means that the wire under test is a fire wire, and vice versa is a zero wire.
Ground test method
Use the red pen on the wire under test, the black pen on the ground or a good contact with the earth on the metal conductor. If the pointer indicates that there is a voltage close to 220V or close to this value, it proves that the wire under test is the fire wire. Zero line to ground no voltage, or only a few volts, but compared with the fire wire, there is still a big difference.
Note: a pen connected to the object under test, the other pen must be connected to the earth and the conductivity of good objects. If connected to a dry wall or the earth, even if there is electricity may not be able to measure the voltage.
Palm winding test method:
The black pen in the left hand or right hand wrapped around a few circles, the other hand holding the end of the red pen on the wire being tested. If the multimeter pointer deflects to the right and there is some voltage, it means it is the fire wire; the one that does not react is the zero wire. However, this method is to use the induced current to measure, easy to be affected by the environmental magnetic field or electric field, the measurement results are not necessarily accurate, for reference only.
Summary
Although the above methods can determine whether the zero line and the fire line and objects are charged, but they have certain disadvantages.
For example, the first method, if the skin is very dry, shoes insulation ability is very good, then the multimeter display voltage may be very low, affecting the results of judgement.
For example, the second one, if the earth wire breaks or the other conductor connected to the other pen is not in good contact with the earth, it may also cause misjudgment.
For example, in the third case, if there is a strong magnetic or electric field around, the measurement result will be completely inaccurate.
Therefore, the safest and most reliable way is still to test with a tester.
