Why use a multimeter to measure a voltage of over 20 volts when the socket is out of power
This is induced electricity.
Impact: It will not affect ordinary equipment and can be ignored. Special precision equipment may cause component damage and requires isolation.
Reason: Mutual inductance with other live power cables laid in parallel
The power socket is out of power, and a multimeter is used to measure a voltage of over 20 volts. This situation is usually caused by poor contact of the live wire of the AC power. A while ago, Mr. Tony's power socket in our village experienced this situation.
Wiring of power sockets.
Mr. Tony is a small farmer and a skilled farmer, but he knows nothing about electricity. I measured the voltage of his home socket with a multimeter, and it was only over 30 volts. Based on experience, if the voltage on the socket is too low to reach the rated value, it is usually due to a problem with live wire contact. So I focused on checking the live wire in his house, searching and searching, and found that the screw connecting the air switch to the live wire was somewhat loose. Tony told me that the live wire almost fell out of the screw hole of the air switch last month, and he inserted the wire himself. I tightened the screw with a screwdriver and measured that the voltage of the socket had increased to 100V. The LED indicator light on the socket also lit up.
The LED indicator light on the socket lights up.
The screws were tightened and the voltage increased to 100V, but it still cannot be used. I continued to search and found that there was an electrical tape wrapped around one of the wires on the courtyard wall. Tony told me that last year many mice crawled along this wire to the grain storage room in the backyard to steal food. Later, he blocked the hole in the room, maybe because the mice couldn't get in and were very angry, biting off the wire.
I checked and found that the interface of this 2.5-square aluminum wire has been severely oxidized, indicating a significant contact resistance, resulting in the socket voltage not reaching 220 volts. So the aluminum wire was cut and reconnected, and electrical tape was wrapped around it. After that, the voltage of the socket was measured to reach 220 volts.
