5 ways to distinguish between induction electricity and leakage electricity

In daily life, when household appliances (such as washing machines, refrigerators, and power tools) leak electricity or are inductively charged, you will feel "numb hands". If you use a test pen to test, both will make the neon bulb of the test pen turn red. If it is just inductive electricity, these household appliances can continue to be used. If it is leakage, it will be very dangerous to continue to use it, and it must be repaired. But how can we correctly distinguish whether it is inductive charging or real leakage?

1. Causes
Inductive charging is caused by the mutual induction between the internal circuit and the shell of the machine or between the circuits. Its charging mechanism is shown in Figure 1, which is equivalent to the connection between the charged part and the shell through the capacitor. Leakage is caused by the aging or reduction of the insulation of the internal circuit due to the long-term use of the machine or moisture, which makes the machine shell charged. Some are caused by the deformation of the shell of the machine, which makes the shell and the internal charged part have one or more direct contacts (it is very dangerous to use the machine in this case), as shown in the figure.

2. Judgment method
1. Resistance measurement method
Use a multimeter to measure the insulation resistance between the machine housing and the circuit, as shown in Figure 3. When the measured resistance value is greater than 1M, it can be considered as induced charging. When the measured resistance value is several thousand ohms or less, it can be considered as leakage, and measures must be taken. This is a relatively simple method and the most commonly used method, but this method is not very reliable and must be further determined by other methods. 2. Load judgment method
Disconnect the neutral line (N line) of the machine, insert a 220V/15W bulb between the breakpoint and the housing, and turn on the power after the connection is good. At this time, if the bulb lights up, it means that the machine has leakage; if the bulb does not light up, it means that the machine is induced charged. This is because the leakage current can be large enough to make the bulb light up, while the induced current is only tens of milliamperes, which is not enough to make the bulb light up. This method is more accurate. 3. Voltage measurement method (I)
Use the voltage block of the multimeter to first measure the voltage between the machine housing and the ground, then swap the live wire (L line) and the neutral wire (N line) of the machine, and then measure the voltage between the machine housing and the ground again. If there is a big change in the voltage values ​​before and after, it is largely caused by leakage; if there is no obvious change in the two measurement results, it means that it is induced charging. This is because the leakage point of the machine is often not in the middle of the normal charged body of the machine. If it is exactly in the middle, the judgment will be wrong, and the results of the two measurements will be different. When the induction is charged, it has nothing to do with the measurement point, so the value will not change. 4. Voltage measurement method (II)
When the machine is running, first use a multimeter to measure the voltage between the machine casing and the neutral line (N line). Stop the machine, disconnect the neutral line (N line), connect the multimeter between the breakpoint and the machine casing, and then only connect the live line (L line) to the power supply, measure the voltage again, and compare the two times. If there is a significant change in the results of the two times, it indicates leakage; if there is no big change, it is mostly caused by induction. This is because the voltage measured for the first time is the voltage between the leakage point and the neutral line (N line) (unless the leakage point is very close to the live line end, it is approximately the power supply voltage), and the voltage measured for the second time is basically the power supply voltage; the two are often different. If it is induced charging, there will be no such value change. 5. Voltage measurement method (III)
Set the digital multimeter to AC20V, then hold one test lead in one hand and another test lead in the other hand close to the machine casing. When the distance is about 4-5cm, observe the multimeter. If the multimeter displays a voltage of several volts (V), it indicates that the charging is caused by leakage; if the multimeter does not display or the displayed value is very small, it indicates that the casing is charged because of induction.
From the above judgment methods, some are simple and some are not very accurate. Therefore, when encountering a situation where the machine casing is charged, several methods should be combined to increase the reliability of the judgment so that corresponding measures can be taken.

3. Measures to be taken
After distinguishing whether it is leakage or induced charging, different measures need to be taken. If the charge is caused by induction, a grounding wire should be installed on the machine casing. In this way, there will be no "numb hands" phenomenon in future use, and it will also play a certain role in protecting the machine from leakage. If the charge is caused by leakage, the machine should be inspected and repaired to find the leakage point, and the insulation should be strengthened or repaired before the machine can be put into use again.