When household appliances (such as washing machines, refrigerators, power tools) have leakage or induction charging, they will feel “numb”. If you use a test pen to check, both will make the neon bulb of the pen turn red.
If it is just induction electricity, these appliances can continue to be used. If there is a leakage, continued use will be very dangerous and must be repaired.
But how can we correctly distinguish between induced charging and real leakag
nductive electrification is caused by the mutual induction between the internal circuits and the casing of the machine or the mutual induction between the circuits, which is equivalent to the capacitance between the live parts and the casing.
Leakage is caused by the aging or degradation of the internal circuit insulation caused by long-term use of the machine or moisture, etc., making the machine shell electrified.
Sometimes it is caused by the deformation of the shell of the machine, which makes one or more direct contacts between the shell and the internal live parts (it is very dangerous to use the machine again in this case).
Judgment method
01Resistance measurement method
Use a multimeter to measure the insulation resistance between the machine shell and the circuit. When the measured resistance is greater than 1M, it can be considered to be inductively charged.
When the measured resistance is several thousand ohms or less, it can be considered as leakage and measures must be taken.
This is a relatively simple method and is the most commonly used method, but this method is not very reliable and must be further determined using other methods.
02load judgment method
Disconnect the neutral line (N line) of the machine, and connect a 220V/15W light bulb between the breakpoint and the shell. After the connection is good, turn on the power. If the light bulb glows at this time, it indicates that the machine has leaked electricity;
If the light bulb does not glow, the machine is inductively charged. This is because the leakage current can be large enough to make the light bulb glow, while the induced current is only tens of milliamps, not enough to make the light bulb light. This method of judgment is more accurate.
03Voltage measurement method
(1) Use the voltage switch of the multimeter to first measure the voltage between the machine casing and the ground, then swap the live wire (L line) and the neutral line (N line) of the machine, and then measure the voltage between the machine casing and the ground. Voltage.
If there is a big change in the voltage value between the two 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 normally 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, the value will not change because it has nothing to do with the measurement point.
(2) With the machine running, first use a multimeter to measure the voltage between the machine shell and the neutral line (N line). Stop the machine, disconnect the neutral line (N line), connect the multimeter between the break point and the machine shell, then connect only the live wire (L line) to the power supply, measure the voltage again, and compare the two results. If there are obvious changes, it indicates leakage;
If there is not much change, in most cases it is charging 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 wire end, it is approximately the power supply voltage), and the voltage measured for the second time is basically the power supply voltage; There is a difference between the two in many cases. If it is induction charging, there will be no such numerical changes.
(3) Set the digital multimeter to AC20V, then hold one test lead in one hand and the other test lead 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 it is charged due to leakage;
If the multimeter does not display or displays a very small value, it means that the case is charged due to induction.
Judging from the above judgment methods, some are simple and some are not very accurate. Therefore, when encountering a situation where the machine casing is electrified, several methods must be combined to make judgments to increase the reliability of the judgment so that corresponding measures can be taken. measure.
Take measures
After distinguishing whether it is leakage or induction charging, different measures need to be taken.
If it is inductively charged, a grounding wire should be connected to the machine shell, so that there will be no “numb hands” in future use, and it will also play a certain protective role against machine leakage;
If the electrification is caused by leakage, the machine should be inspected, the leakage point should be found, and the insulation should be strengthened or repaired before the machine can continue to be put into use.
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Post time: Oct-27-2023