In the dark night, I finally finished my day’s work. Just before I lay down to sleep, I just plugged the phone charger into the outlet, when suddenly I heard a snap, and a flash of light was particularly conspicuous in the dark house. Pull out the plug and see:
The plug is black｜yam.com
I searched the Internet and found that there are many complaints about the plug turning black . Can the blackened plug continue to be plugged back in? Will there be another “lightning” suddenly at night and cause a fire?
Too long not to read the version
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When inserting the plug, the occasional electric light is caused by air breakdown, so don’t worry about it;
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Plugs and sockets that turn black require inspection. If the plastic at the joint is deformed, you’d better stop using it and replace it as soon as possible.
Flash once in a while? don’t worry
It is not uncommon for electric sparks to appear when plugging and unplugging, and it belongs to air breakdown .
When people use plugs to plug into sockets, it is a process of connecting electrical appliances to the large power grid. The electricity from the grid enters our electrical appliances through the plugs. When the plug is about to touch the metal plate in the socket, there is always a time when the distance between the plug and the metal plate in the socket is very short. At this time, although there is no touch, there will still be a spark flash.
The principle of this flash is similar to that of lightning: generally speaking, air is an insulator, but if the voltage is large enough or the distance is short enough, the air will break down and conduct electricity.
Lightning in Nature丨Pixabay
When a voltage is applied, a small number of electrons are emitted from the electrodes, and there may be a small number of charged particles in the air, which begin to accelerate under the action of the electric field and constantly hit passing particles in the air. When these particles are knocked apart, new electrons and charged particles are also created. These particles are accelerated together by the electric field, and then continue to collide with other particles.
In this way, one collision produces two, two collision produces four, and it keeps increasing. If the voltage is large enough and there are enough charged particles, a conductive path is formed, which results in a breakdown.
This voltage is about 3.3kV/mm in the air, that is, if our hands are 1 mm away from the 3.3kV wire, the air will be broken down, and we will be “electrically shocked”. In practical applications, due to the irregular shape of the wire and unclean air, the breakdown voltage may be much lower, and the air will be more easily broken down.
A breakdown like this looks scary, but who hasn’t seen it in life? In winter, when you touch the doorknob, there will be static electricity, and in summer, the electric mosquito swatter and the electric mosquito will be sparked, the essence is that the air is broken down. Some people may dislike the feeling of being over-charged, but who can refuse the sound of sizzling barbecue? Even, in many laboratories, people will deliberately create air breakdown for research.
“Manufacturing” air breakdown in the laboratory丨Photo courtesy of the author
So the question is, is the air breakdown phenomenon in the plug dangerous?
Are these gorgeous fireworks safe?
For electrical appliances, such sparks will have some impact. Breakdown means that a large current flows through the consumer in a short period of time. Electrical appliances subjected to such a large current for many times may cause the degradation of equipment performance and shorten the life of the battery.
While sparks like this do happen from time to time, there are changes we can make to minimize its consequences.
For example, when charging a mobile phone, you can plug in the charging head first, and then plug in the mobile phone; when not charging, unplug the mobile phone first, and then unplug the plug. When using other electrical appliances, plug in the plug first, then turn on the switch; turn off the switch first, and then pull out the plug. In this way, even if a spark occurs between plugging and unplugging, its influence can be minimized.
Secondly, this spark is a type of “surge” in the electrical field. Some power strips will have anti-surge function. If the anti-surge plug-in strip is used, the impact of such sparks can also be reduced.
What if the electricity is “black”?
Sometimes when you pull out the plug, you will find that the plug and socket have turned black. At this time, you need to pay attention.
The plastic on the plug turns black, you need to observe the shape of the black first. If the plastic is obviously deformed, or the black on the surface cannot be wiped off, it is likely to be caused by thermal deterioration . A large current flowed through one or more times, and a small part of the plastic of the plug was burned. Although such blackening may continue to serve, it is still recommended to change a plug .
The two metal sheets of the plug are black, mainly because the metal surface is oxidized. Repeated over-powering will also slightly “burn” the metal sheet of the plug. Such a plug is not completely unusable, but the increase in contact resistance will make the contact poor and may cause new problems. Generally speaking, pickling can be used to remove the oxidized part and restore the metallic luster. But for most users, replacing with a new one is still the most convenient option.
If the socket is blackened, it needs to be checked like the blackened plug. When checking, the power should be cut off in advance, and more caution is required. Some are visible to the naked eye, and they are too dark to look like. You should call a master electrician to overhaul them.
The sockets placed in the corners of the house also need to be checked regularly. Even if they are not burnt black, they must be cleaned.
Image credit: burnshield.com
Most sockets are designed with over-current protection devices, and the household air switch also has short-circuit protection. Even so, electrical safety is still very important.
In daily use, the number of plugging and unplugging can be reduced as much as possible, and the frequency of sparks and blackening can be observed at the same time. Once sparks occur frequently, or there are obvious changes in plugs and sockets , it needs to be handled carefully.
references
[1] There is a way to correctly charge mobile phones, “State Grid News”, January 06, 2022, 8th edition
Author: Madoka
Edit: Owl, Window Knock Rain
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