Why is there more than 20 volts measured with a multimeter when the socket is dead?
Impact: It will not affect ordinary equipment and can be ignored. For special precision equipment, it may cause damage to components and need to be isolated.
Reason: caused by mutual inductance with other charged power cables laid in parallel
The power outlet is out of power, and there is a voltage of more than 20 volts measured with a multimeter. This situation is generally caused by a poor contact of the live wire of the AC. Some time ago, this happened to the power outlet of Mr. Tony’s house in our village.
Using a multimeter to measure the voltage of the socket in his home, it was only over 30 volts. According to experience, if the voltage on the socket is too small to reach the rated value, it is generally because there is a problem with the live wire contact. So I focused on checking the live wires in his home, searching and searching, and found that the screws connecting the air switch to the live wires were loose. Tony told me that the live wire was about to fall out of the screw hole in the air switch last month and he plugged that wire in himself. I tightened the screw with a screwdriver, and the voltage of the measuring socket rose to 100V, and the LED indicator on the socket also turned on.
Tightened the screws, and the voltage went up to 100V, but it didn't work yet. I then searched and found that one of the wires on the courtyard wall was wrapped with electrical tape. Tony told me that last year, many mice crawled along this wire to the room where the grain was stored in the backyard to steal food. Later, he blocked the hole in the house. Maybe the mice couldn’t get in. He was very annoyed and bit off the wire up.
The interface of this 2.5 square aluminum wire has been severely oxidized, so there must be a large contact resistance, which leads to the socket voltage not reaching 220 volts. So I cut off the aluminum wire and reconnected it, and wrapped it with electrical tape, and then measured the voltage of the socket to reach 220 volts.
