Why ground

Greetings to the Khabrovites.

Who is this post for

Those who know and understand why grounding is needed will not discover anything new. When I made this discovery for myself, I was surprised to find that many of my friends (IT-related) have little understanding of why grounding is necessary at all. Therefore, actually now you see this post.

Background

Having bought new headphones with a microphone, and having arrived home - I sadly found that the microphone was creating an extraneous noise. I returned to the store, there we checked on the laptop, there was no extraneous noise from the microphone. Arriving home, I began to look for a reason. I connected the old headphones, do not make noise. Reconnected new headphones, noisy. After some time, I accidentally touched the system unit with my foot, and lo and behold, the noise was significantly reduced.

So, I came to the conclusion that some kind of interference occurs on the system unit case. I immediately had the thought of grounding, and I climbed to measure the voltage of the housing relative to the ground. 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.

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

Where did the tension come from?

I will not go into details of where the voltage comes from on the cases of refrigerators / washing machines. I can only 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 this:
In the computer’s power supply there is a filter that attenuates high-frequency interference and dumps them into the ground. But actually this filter itself:

Thus, 110V goes to the ground (if 220V is in the socket), but the current is only an interference current, which means that the current strength will be insignificant.
But such a device is probably familiar to everyone:

Подводный камень данного девайса заключается в том, что он связывает заземления всех устройств, включенных в него. Если у вас включено N системников в него, то ток, отфильтрованный каждым фильтром в БП будет складываться, и находиться на корпусе каждого системника будет уже сумма ;) Кроме того, как показали мои «измерения земли» — точно такие же фильтры находятся в мониторах (по крайней мере в обоих моих мониторах именно так).

Чем это грозит

Even adding up the current from 5-6 devices connected to the aforementioned surge protector, it 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 breaks? You can easily get the full 220 on the body of your system unit. Of course, capacitors are chosen with such a rated voltage so that breakdown does not happen even from strong surges (in the above 2kV circuit, for example), but as they say once a year, the bastard will shoot. But this is not the worst.
The main charm is that devices designed for grounding are designed as if you have grounding. the device rightfully believes that in case of an emergency it can discharge excess current into the ground. The diagram above shows that the land I circled is not the only one. And how many potential places you have is unknown. Thus, without the existing grounding, a life-threatening voltage can easily form on the body of your appliance.

And the most horror

It is especially dangerous in this way to use devices that somehow work with water. For example, washing machines or dishwashers. In a washing machine, for example, the heater may leak out, and there will be full 220V on the case, 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 fatal

conclusions

I hope those who still do not have grounding, I convinced him to do it. In the end, I’ll just say, do not make grounding as simple and quick as possible (for battery, grounding, etc.), do it right, because it is not only your personal safety, but also the safety of others.
On a habr there are articles on how to do 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 an RCD, because it can be connected to the circuit without grounding . However, not without flaws