Why ground

Greetings Habrovtsev.

For whom this post

Those who know and understand why grounding is needed will not discover anything new for themselves. When I made this discovery for myself - I was surprised to find that many of my friends (connected with the IT sphere) poorly understand why they should be grounded at all. Therefore, actually now you see this post.

Background

Having bought new headphones with a microphone, and when I came home, I sadly found that the microphone was creating extraneous noise. I returned to the store, we checked it on the laptop, there was no extraneous noise from the microphone. Arriving home began to look for the cause. Connected old headphones, no noise. Again plugged in new headphones, make noise. After a while, I accidentally touched the system unit with my foot, and about the miracle the noise decreased significantly.



So, I came to the conclusion that some sort of interference occurs on the system unit case. I immediately had a thought about grounding, and I used to measure the voltage of the body relative to the ground. At first I took the ground wire for the ground, and was surprised to find that the potential difference was about 100V. I decided to measure the voltage relative to the heating battery, all the same ~ 100V.

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It became curious, decided to google, and as it turned out I was far from the first:

Where does the tension come from

I will not go into details of where the voltage on the cases of refrigerators / washing machines comes from. Let me just say that the reason in 99% of cases is the same as on the case of the system unit. In Google you can find a more detailed description and explanation. In short, the reason is:

In the power supply unit of the computer there is a filter, extinguishing high-frequency interferences, and dropping them into the ground. But actually this filter itself:



Thus, we are going to the ground 110V (if the outlet is 220V), but the current is only the noise current, and therefore we will have a small current.

But such a device is probably familiar to everyone:



The underwater stone of this device is that it connects the ground connections of all devices included in it. If you have N systemists in it, then the current filtered by each filter in the power supply unit will be added up, and the sum will already be on the body of each system unit;) In addition, as shown by my “ground measurements” - exactly the same filters are in the monitors ( at least in both of my monitors that way).

Than it threatens

Even adding current from 5-6 devices connected to the aforementioned surge protector is unlikely to be so strong as to kill a person. But there are other pitfalls.

What happens if one of the filter capacitors suddenly strikes? You will easily get a full 220 on the case of your system unit. Of course, the capacitors are selected with such a rated voltage that the breakdown does not happen even from strong jumps (in the above diagram, for example, 2kV), but as they say once a year and the bastard shoots. But this is not the worst.

The main charm is that devices designed for grounding are designed as if you have a grounding. the device rightly believes that in the event of an emergency it can dump excess current into the ground. The diagram above shows that the land I circled is not the only one. And how many such potential places you have is unknown. Thus, without existing grounding, life-threatening voltage can easily form on the housing of your appliance.

And the most horror

It is particularly dangerous in this way to use devices, one way or another working with water. For example washing machines or dishwashers. In a washing machine, for example, the heating element can leak, and the case will have full 220V, and since the washing machine is often located in the bathroom, where there is tile and moisture, you will be an excellent conductor, and the electric shock will most likely be lethal.

findings

I hope those who still do not have grounding, I convinced him to do. Finally, let me just say, do not make the grounding as easier and faster (on the battery, zeroing, etc.), do it as it should, because it is not only your personal safety, but also the safety of others.

On Habré there are articles on how to properly do the grounding . You can also google a lot of information about this.



Well, thank you for your attention. ;)

UPD. Through the efforts of TolTol , vertu77 , juray, I realized that you can significantly protect yourself using RCDs, since it can be connected to the circuit without grounding . However, not without flaws