Why is the voltage at the socket more than 20 volts measured with a multimeter when there is no power?
This is induced electricity.
Impact: It will not affect ordinary equipment and can be ignored. Particularly precise equipment may cause component damage and needs to be isolated.
Reason: caused by mutual inductance with other live power cables laid in parallel
The power socket is out of power, but the voltage measured with a multimeter is more than 20 volts. This situation is usually caused by poor contact of the AC live wire. Some time ago, this happened to the power socket at Mr. Tony's house in our village.
I used a multimeter to measure the voltage at the socket at home, and it was only over 30 volts. According to experience, if the voltage on the socket is too low to reach the rated value, it is usually caused by a problem with the live wire contact. So I checked the live wire at home and found that the screw connecting the air switch to the live wire was somewhat loose. Last month, the live wire almost fell out of the screw hole of the air switch, so he inserted the wire himself. I tightened the screw with a screwdriver and measured that the voltage of the socket increased to 100V, and the LED indicator light on the socket also turned on.
After tightening the screws, the voltage increased to 100V, but it is still unusable. Then I searched and found that one of the wires on the courtyard wall was wrapped with electrical tape. Last year, many rats climbed along this wire to steal food from the grain storage room in the backyard. Later, he blocked the holes in the house. Maybe the mice couldn't get in. They were very annoyed and chewed off the wire.
I looked at the interface of this 2.5-square-meter aluminum wire and it was severely oxidized. There must be a large contact resistance, resulting in the socket voltage not reaching 220 volts. So I cut the aluminum wire, reconnected it, and wrapped it with electrical tape. Then I measured the socket voltage and it reached 220 volts.
