Recently, a friend asked the editor a question, saying that his home tripped when there was a power outage and went to inquire about the property. The property maintenance worker said that it was because the air switch was too sensitive and was very distressed.

The property’s statement is obviously nonsense. Ordinary MCBs only have the function of overload protection for the circuit. The so-called “sensitivity is too high” can only be because the MCBs are too small, but they will only trip during normal use. , It is impossible to trip before power failure.

The editor went to a friend's house and found that the air-opening in his house looked like this:

It is the device on the right that causes the tripping when the power fails.

In fact, this thing is called "undervoltage release", which is installed on the air switch as an accessory, and its function is to protect the circuit from undervoltage. When the voltage in the circuit is too low during a power failure, the device will automatically trip the circuit breaker.

It is similar to the leakage protector in usage and appearance, so many people think it is a leakage device.

There are two changes to the undervoltage release during undervoltage tripping. One is that the reset button of the undervoltage release will protrude and cannot be closed directly. You need to press the button to close normally. The other is the blue square reset button on the right side of the figure above is a display screen, the screen is green during normal use, the screen turns red after tripping, can be closed directly after tripping, and the screen returns to green after closing.

Regardless of whether it is an undervoltage release or a leakage protector, any circuit breaker with such accessories should first check the status of the accessories after tripping, so as to determine the cause of the circuit failure.

If the tripping is caused by the action of the undervoltage release protection device when the power is out, there is no need to overhaul, just close the switch directly. If it is troublesome, you can replace the circuit breaker without undervoltage protection or remove the undervoltage release device (Not recommended).