Why must residential electrical systems be connected to Earth (soil)?

[DaveE]

What is good primary protection and good construction?

It's what's written in your local building code book(s). Sometimes it's not simple or obvious, that's why the books are big. Sorry, I don't want to read them to you, you'll just ask us more questions without actually studying the subject. I think I'm done.

 

[gen x]

In the case that I gave the conduit was a protective sleeve that terminated into the switch box. I won't comment about if it was safe at the time of original installation. The conduit did not run all the way to the breaker panel.
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As far as what is good primary protection and good construction:
Ideally in my opinion the safest would be to have what we have now in the USA. The neutral is tied to the chassis of the meter can as well as the main breaker panel. After this the protective ground is kept separate from the neutral. Every piece of metal associated is bonded to the protective earth. Water piping is also bonded to the protective ground. Ground rods are driven and connected to the main panel. Concrete encased electrodes are also used. A length of rod is encased in the concrete footing of the building. GFCIs have become quite reliable concerning nuisance trips. One thing that could be changed is to keep the neutral and protective ground separate all the way to the transformer. I've thought this could be an added layer of safety but I am not so sure. The protective ground wire en route to the transformer could be broken without being known until it's really needed. This could result in the chassis of every appliance developing a voltage in the event that somehow the protective earth system in the house becomes energized.

In my country(EU), we have TN-C-S and TN-S system, every house must have earthing with minimum 15m long galvanized steel strip buried into soil, this strip is connected to steel rods stuck deep into soil. Only after the inspection examines the grounding, you can get a connection permit.

 

[Hornbein]

Isolated/floating systems are also used in places where a fault would otherwise trip a breaker and the loss of power would cause a large loss in revenue or other problems. The system is monitored and if a fault exists it is tracked down and dealt with while the power is on.
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Hospital operating rooms work with isolated systems. My memory isn't what it used to be but it seems I may have posted a link to a good YouTube video on the subject at some point in the last couple of years. I'll do a quick search.

Huh. I learned something here.

In my country(EU), we have TN-C-S and TN-S system, every house must have earthing with minimum 15m long galvanized steel strip buried into soil, this strip is connected to steel rods stuck deep into soil. Only after the inspection examines the grounding, you can get a connection permit.

15m! And even that isn't enough. Amazing. Maybe some day I'll find out what a ground loop is.

 

[Averagesupernova]

It is my opinion that the electrodes driven into the earth need to be good enough to reliably trip a GFCI. In other words, the resistance in that part of the circuit needs to be low enough so that they do not add enough resistance to become a significant part of the total resistance between the hand of the person touching a live conductor and the neutral node on the transformer.

 

[gen x]

It is my opinion that the electrodes driven into the earth need to be good enough to reliably trip a GFCI. In other words, the resistance in that part of the circuit needs to be low enough so that they do not add enough resistance to become a significant part of the total resistance between the hand of the person touching a live conductor and the neutral node on the transformer.

Yes low resistance of earth is important but in pratice, when hot wire touch metal case, 99% of current return via neutral as it explained below, I think it will be dangerous if that link dont exist and we rely only on earth as return path.
Do you agree?

 

[Averagesupernova]

Yes low resistance of earth is important but in pratice, when hot wire touch metal case, 99% of current return via neutral as it explained below, I think it will be dangerous if that link dont exist and we rely only on earth as return path.
Do you agree?

I already told you I was not going to chase every link you provide.
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What you are describing I already described in post #30.

 

[Babadag]

I agree with the statement: the ground [earth] will be the same potential as the normally non-current carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment. However, it is not exactly.
N.E.C. Art.250 considers as the maximum voltage [on low-voltage installation] to ground, on the ungrounded conductors, does not exceed 150 V.
The fault clearing time is very important also. Shorter time permits a higher voltage.
On grounded systems the fault to ground current is higher. Then the clearing time is shorter if the current is higher so the protection may act quickly.
For high-voltage systems the grounding electrode is a grounding grid where the short-circuit to ground produces touch and step voltage drop of a limited level with respect the fault clearing time. Even if the system is not grounded the phase-to-phase short-circuit occurs and the and the current rises in the same way.