I just had (and solved thanks SE) a problem with a wall socket where the ground contacts were malfunctional. Much of the electrical safety relies on proper grounding. As far as I can read, details for state-of-the-art measurement of grounding is a science for itself, but the described methods seem far from impossible to do.
I want to test grounding of each socket (and possibly measure resistance for monitoring) as far as possible and practical for safety reasons (personal protection, possibly reduce noise (especially bad with telephone at my parents' house), and obvious prerequisite for surge protection).
Question: What are practical, safe and economic ways for a technically skilled person, but not regularly trained as electrician? E.g. 3 or 4 wire measurements with earthing, "measuring probe" and "helping-earth probe"? In particular, I am not specifically interested in one earthing metal pole but in the earthing as such that "arrives" at the sockets.
I live in an area with houses and small gardens, but with low distance to other houses/streets (5-50 m distance in all directions). So far, I could not figure out in what way my apartment house is (or: should be) grounded (no answer from landlord, I think they do not know themselves). Is it then necessary to disconect the earthing pole from the rest of the house as I read somewhere? (Seems that this was primarily meant only to test one specific earth pole independent from possibly other earthing poles)
I am willing to spend some money, but not necessarily hundreds of dollars/euros per household. I see devices (from cheap (24 €) to expensive (174 €), all still affordable) such as this, this, this and this. Price would be ok as I can use it for my family and friends as well, this is why I'd prefer DIY (if considered safe). Do such devices offer a valid approach to my question?
Disclaimer: All electrical engineering of the house was done by certified electricians (at least I hope so), and I do not want to change anything - unless I discover a problem and will then obviously ask a certified electrician to solve it if it requires work on the mains.