What is the difference between earth and earth from a power outlet?

Question

I'm having a real difficult time understanding the following statements from various sources:

That's what I was told: don't use the earth pin from a power outlet as your earth because it's dangerous.

Source: Q: Using the earth pin on a power outlet as the earth for a crystal radio (while writing this question)

Similarly, on reddit, there are comments telling a very similar story:

Do not connect anything w.r.t. ground to your wall outlet! That‘s a recipe for disaster.

Source: /r/homelab - Grounding your server rack ?

In your house, don't worry about it.

Grounding to the outlet ground is not an earth ground return and potentially dangerous.

Source: /r/homelab - How many of you ground your equipment/server rack? (emphasis mine)

I tried to read and understand the arguments made by the people who claim this is the case, but I don't really understand what they're getting at.

To add further to my confusion, there are people saying the exact opposite of what the above sources say.

Now, I'm not an electrician and I don't consider myself an electrical engineer anymore, but I do have knowledge about electrical engineering. I completed a 4 year apprenticeship on electrical engineering.

I do know that grounding plays a very important role in electrical safety, and to my knowledge, all consumer products made out of metal have the ground pin attached to the housing if they're powered with mains power.

So, if Grounding to the outlet ground is not an earth ground return and potentially dangerous. is the case, why are all these products made out of metal connected directly to it (outlet ground)? That doesn't make any sense to me.

If that makes any difference, yes, this is in the context of grounding a network rack.

However, I don't think that plays a hugely important role, unless I'm missing something here.

Please note: I'm not asking why grounding is done, or what earth's ground is. I'm simply confused by the statements that one shouldn't use the earth from a wall outlet as earth ground: to me, they are the same thing, just with a different "wiring" - lets say.

Context (if this is necessary): I'm living in Switzerland.

Answer 1

The risk is that in the event of a dead short occurring in between live and earth, the PE could present a significant voltage momentarily until the fuse/breaker trips. The earth connection should present a very low resistance to ground, but if this ground happens to be a spike hammered into the ground then it doesn’t guarantee to be a much better conductor than anyone who happens to be touching the PE at the time. So the risk is small but the fallout could be dire.