The reasons are:
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1. The charger leakage leads the dangerous voltage to the 5V ground of the mobile phone power supply;
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2. The mobile phone has a metal coating or metal edge, and the metal edge is connected with the ground wire;
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3. When people touch the metal edge, other parts of the body are grounded, forming a circuit to the ground;
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4. Failure of leakage protection device at home, or none at all;
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5. When this danger occurs, there is no one nearby to help timely power off.
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Extended data
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1. Discharge static electricity during cleaning. Clean the charger and charging port regularly. When cleaning, use a damp cloth, or an antistatic cloth. Do not use dry cloth (electrostatic charge).
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2. Waterproof and moisture-proof. As an electronic product, accidentally entering water or being exposed to humid air when not used for a long time will cause varying degrees of corrosion or oxidation of its internal electronic components.
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3. Anti-fall and shock. The mobile phone charger is actually a fragile part, and the internal components can not withstand beating. In particular, it is necessary to prevent accidental landing during use. Do not drop, tap, or vibrate the charger. Handling the charger roughly will destroy the internal circuit board.
It's inductive electricity. The vast majority of ordinary mobile phone cases are plastic, so this phenomenon you said is not common.
However, there are also mobile phone cases that are metal, when charging, if the quality of the charger is not very good, there may be pulsating direct current induction to the mobile phone case, or there is an alternating current component string into the low-voltage side, then it is possible to feel the feeling of electricity on the metal shell.
That may be your mobile phone leakage, most mobile phone cases are made of plastic or silicone material, generally do not conduct electricity, but if you use a mobile phone case is made of metal material, conduction means that the mobile phone leakage occurred, it is best to take the mobile phone to the official sales center to test, so as not to cause unnecessary safety accidents. If it is a line fault, simple maintenance can be returned to normal