When electric leakage or induction electrification occurs in household appliances, there will be a “numb hand” feeling. If the test pencil is used for inspection, both of them will make the neon bubble of the pencil red.
If it is only inductive electricity, these appliances can still be used. If it is electric leakage, it will be very dangerous to continue to use, and maintenance must be carried out.
But how can we correctly distinguish between inductive charging and real leakage?
Inductive electrification is caused by mutual induction between lines inside the machine and the shell or between lines, which is equivalent to the connection between the live part and the shell through capacitance.
Leakage is caused by aging or decreasing of internal circuit insulation due to long service life or damp of the machine, which makes the machine shell live.
Some are caused by the deformation of the shell of the machine, which makes the shell directly contact with one or more internal live parts (it is very dangerous to reuse the machine in this case).
01 Resistance measurement method
Use a multimeter to measure the insulation resistance between the machine shell and the line. When the measured resistance is greater than 1M, it can be considered as induction electrification,
When the measured resistance is thousands of 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 reliable and must be further determined by other methods.
02 Load judgment method
Disconnect the zero line (N line) of the machine, connect a 220V/15W bulb between the breakpoint and the housing, and connect the power after the connection is good. If the bulb lights up at this time, it indicates that the machine has leakage;
If the bulb does not light up, it indicates that the machine is inductively 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 relatively accurate.
03 Voltage measurement method
（1） Use the voltage gear of the multimeter to measure the voltage between the machine shell and the ground, then exchange the live wire (L wire) and the neutral wire (N wire) of the machine, and then measure the voltage between the machine shell and the ground.
If there is a great change in the values of the two voltages, it is largely caused by leakage; If there is no obvious change in the results of the two measurements, it means that it is inductive electrification.
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 happens to be in the middle, the judgment will be wrong, and the results of the two previous measurements will be different.
When the induction is electrified, the value will not change because it has nothing to do with the measuring point.
（2） With the machine running, first use a multimeter to measure the voltage between the machine housing and the zero line (N line). Stop the machine, disconnect the zero line (N line), connect the multimeter between the breakpoint and the machine shell, then connect the live line (L line) to the power supply, measure the voltage again, and compare the results of the two times. If the results of the two times have obvious changes, it indicates that it is leakage;
If there is not much change, it is charged by induction in most cases. This is because the voltage measured for the first time is the voltage between the leakage point and the zero line (N line) (it is approximate to the power supply voltage unless the leakage point is very close to the live line terminal), and the voltage measured for the second time is basically the power supply voltage; The two are different in many cases. If it is inductively charged, there will be no such numerical change.
（3） Turn the digital multimeter to AC20V gear, then hold one probe with one hand and the other close to the machine shell. When the distance is about 4-5cm, observe the multimeter. If the multimeter shows several volts (V), it indicates that it is electrified due to leakage;
If the multimeter does not display or the displayed value is very small, it indicates that the enclosure is charged because of induction.
According to the above judgment methods, some are simple and some are not accurate. Therefore, when the machine shell is charged, several methods should be used to judge each other, so as to increase the reliability of judgment and take corresponding measures.
After distinguishing whether it is electric leakage or inductive electrification, different measures need to be taken.
If it is inductive electrification, a grounding wire should be made for the machine shell, so that there will be no “numbness” in future use, and it will also play a certain role in protecting the machine from electric leakage;
If the electrification is caused by electric leakage, the machine should be overhauled to find out the leakage point, and the machine can only be put into use again after the insulation is strengthened or repaired.