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.

 

[Babadag]

From the international [ and British ] standard for grounding in power installation exceeding 1 kV:

 

[gen x]

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.

Why is 150V on ungrouding(flaoting) system? Doesnt have to be zero volts?

 

[Babadag]

The voltage between a grid[the grounding of the installation] and the equipment non-energized part connected with is VFH in the attached fig.7[from IEEE 80/2013 Standard].
In order to get 0 V for this parameter you need Rg [ground resistance] =0.
It is not possible even if we try to do this with any cost.
The NEC limited this resistance to 25 V [maximum] and the voltage VFH=150 V

 

[gen x]

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

I write wrong, we have galvanized steel strip all the way to the transformer, so that is excelent grounding

 

[adebo]

Wherever persons can be in contact with electricity with voltage above 60 volts, the salty fluids inside their bodies can become a conducting path to electrons, which could interfere with the electrical control impulses reaching their muscles, especially the very important one named heart.

Creating an equal potential between the ground on which those persons stand, barefoot sometimes, and another surface, or between two separated surfaces which can be reached with the hands, eliminates the danger of having a dangerous flow of electrons through the path of their bodies.

Please, see:
https://www.nfpa.org/en/news-blogs-.../03/14/How-Grounding-and-Bonding-Are-Achieved

https://www.salinas.gov/files/sharedassets/city/v/1/fire/documents/grounding-bonding-fact-sheet.pdf

https://www.ecmag.com/magazine/arti...p-to-code-understanding-grounding-and-bonding

https://www.ecmag.com/magazine/articles/article-detail/what-on-earth-connecting-up-to-code-part-2

Beautiful explanation!

 

[Rajesh52]

Why is grounded electrical system safer than isolated system?

A grounded system is generally considered safer because any ground fault creates a low-impedance path, allowing a high fault current to flow. This quickly trips the protective device (fuse or circuit breaker), removing the fault before it becomes dangerous. It also helps keep exposed metal parts close to earth potential, reducing the risk of electric shock. In contrast, an isolated system may continue operating after the first ground fault, but the fault is harder to detect, and a second fault can lead to a much more serious short circuit.

 

[sophiecentaur]

In contrast, an isolated system may continue operating after the first ground fault, but the fault is harder to detect, and a second fault can lead to a much more serious short circuit.

There is no simple answer to the earthing question but, in most permanent installations there can't really be any reason not to bond everything metallic to a common potential point (i.e. Earth). Earth (not the planet!!) has a long and complicated history but, users can rely on any exposed metal object being at very near the same potential then the risk of shock is low for faults which have a high resistance / low Earth current. These days, this can be detected by an RCD but, not too long ago, many people were protected in this way without their knowledge.

Proper fusing (single pole in the live leg) will protect against low resistance paths to the Earth system when the Earth current is high enough to blow the fuse. This 'should' protect against the risk of fire, as long as the fuse is appropriate for the supply conductors. Fuses will / should protect against over-current between Line and Neutral where there's no risk of shock.

A second earth fault should be detectable on an isolated system but it would mean that every 'yellow transformer' on a work site would need some sort of RCD which would get in the way of the elegant simplicity of the standard rugged transformer and it could turn itself off at very inconvenient times (fail itself). Even more safety inspections and tighter regs would be called for. And that would increase the cost of all work. 'Repairs' by operators should be forbidden, perhaps. A guy who has been working on a heavy duty concrete breaker would be in so state to do his own repairs with a screwdriver and tatty old cutters. Quite a can of worms, imo.

 

[sophiecentaur]

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.

It would be difficult to achieve this in multiple occupancy buildings with many floors and no surviving records of tests. In UK, the supply to the house is usually provided with an armoured sheath which is connected to the Neutral conductor back at the transformer. (TN) That is considered to be a 'good enough' Earth connection and the loop impedance will be well below 1Ω.

My UK house is 100 years old and started life with an underground DC supply. There appears to be no continuity between the armoured cable and the Neutral and this is the same for all(?) the houses in the street. The Earth Loop impedance measured at well over 100Ω and the Network Authority man who came to see it would not provide a measured value. They were, in fact, very 'shifty' about it, no doubt because providing a TN type system to the whole street / district would be far too expensive.
My sparks provided me with a local copper Earth spike and the Impedance is only a very few Ohms. Low enough for my handy plug tester to be satisfied and I think it can now be regarded as a TT system. I certainly feel fairly safe (and it's wall-to-wall RCDs).