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I have a need to install earthing on an existing building which does not have space to dig a hole for new conductor.

The building has an old water bore which is no longer in use. The Pipes for water bore are not in commission anymore and were sealed from the top a decade ago with Cement. After removing Cement, the pipes are in good condition and pass a resistance test for Earthing. Can I use these pipes as a Earthing Conductor? The local building codes allow use of these pipes as Earthing Conductor.

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My question is about the depth, since the pipes are buried about 100 feet into the ground and are in contact with underground water.

Would it cause an issue to nearby water bores? Is it possible for earth fault to use underground water as conductor and reach another bore say 100 meters across this building and cause electrocution, or maybe I am thinking too much here?

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    \$\begingroup\$ I find it very unlikely that this is permitted under your local building codes. \$\endgroup\$
    – jwh20
    Nov 4, 2021 at 12:39
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    \$\begingroup\$ Aside from the purely electrical aspects, you might consider asking a separate question on diy.stackexchange.com about the building regulation / code enforcement issues. \$\endgroup\$ Nov 4, 2021 at 12:52
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    \$\begingroup\$ Tomorrow someone will replace a section of the water pipe with plastic and it won't be a ground any more. \$\endgroup\$
    – user253751
    Nov 4, 2021 at 12:58
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    \$\begingroup\$ I thought the purpose for grounding metal water pipes was to prevent then from becoming hot (with voltage) should a short develop someplace between wiring and the pipes. And not as a ground for the electrical service. \$\endgroup\$
    – SteveSh
    Nov 4, 2021 at 14:21
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    \$\begingroup\$ I have no idea about codes, but practically speaking this will be an excellent earthing method and no more likely to lead to shocks or electrocution than any other method. The only problem I see is that you may get excessive corrosion where the copper wire interfaces with the steel pipe. This corrosion may eventually lead to high resistance in the earth path. Also, sometimes wells have steel pipe in the upper section only, transitioning to plastic in the lower sections. But even if this is the case, the upper section by itself will make a great earth electrode. \$\endgroup\$
    – mkeith
    Nov 4, 2021 at 16:54

2 Answers 2

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Maybe take a look at some schematic pictures how proper grounding is constructed, as a solid basis for overvoltage protection, in buildings, per modern norms (in the E.U. and in the U.S.).

The essential point is:

  1. on the inside, the building should have a central star ground, called "protective earth" or PE potential, somewhere at its base. If there's no native metal structure to serve as an inherent PE potential (i.e. the building is not a metal tower or some such), the building must be equipped with a wiring system, comprising such a centralized PE system, distributed throughout the building. Those are all the yellow-green conductors in your three-conductor mains wiring/cabling. There will be a large busbar somewhere in the main wiring cabinet (in the basement or at the ground floor) where all those yellow-green wires join, coming from the whole building. There will be similar busbars, just probably smaller, in any wiring cabinets - the central cabinet per floor, or various smaller tributary wiring cabinets. In terms of safety, the yellow-green busbar is always the most important element of a wiring box or cabinet.

  2. the building will also have an outdoor ground, called the lightning collector and down-conductor system. Imagine this like a cage outside the building, with spikey collectors on the roof, and with a "grid" or even just a "ring" buried just under or in the concrete of the building's foundations. When building the concrete foundations of a modern building, the building plans typically mandate that a metal stripe be buried under the foundations of the perimeter walls - preferably a stainless steel stripe, or at least a zinc-galvanized iron stripe, like 30x4 mm cross-section. Plus there may be additional grounding electrodes. Again the point is to bolt the whole outside cage (lightning collector system) to comprise a common potential, that's electrically anchored to the underlying earth. Where I live in central Europe, 99% of the lightning strikes are within 200 kA of peak current. Now imagine if your lightning collector system has a resistance to the earth of 100 milliOhms (I believe the norms are not even as strict as this). Uncle Ohm says that 200 kA * 0.1 Ohm = 20 kV peak voltage. You don't want this to appear across the inner wiring of your building, so the ouside lightning conductor must stay principally separate from your indoor PE yellow-green star (with an important exception, mentioned in the next paragraph). Which has interesting implications if you need outdoor radio antennas or overhead communication wiring come into the building - but that's probably a whole different fairy tale.

Now comes the promised exception: the outdoor lightning conductor earth, and the indoor yellow-green tree, must be interconnected as well - at a precisely mandated spot, at the bottom of the building! I.e., the central inner equipotential busbar of the PE system within the building must be interconnected to the base of the outdoor lightning protection system. Thus, all the grounds across the building "are one", and if a lightning strikes, it gets earthed through an ouside path to the underlying earth - while the inner yellow-green PE system does not receive a direct spanking (inevitably there would be some residual EM-induced noise, from the lightning pulse just sliding through the outdoor down-conductors).

Anything outside gets grounded to the outdoor lightning down-conductor system. Railings on balconies, sheet metal "trimmings" on the roofs, antenna masts, metal things on chimneys, you name it. Anything inside gets grounded to the yellow-green spider. Such as, any overvoltage arrestors, clipping the voltage on various "nodes" for various purposes. The yellow-green ground circumvents circuit breakers, including the special "balanced" ICCB's that detect "dangerous touch" (leak from the system of live+return).

Incoming mains cabling brings an earth conductor with it. It's a single "return" conductor, shared by the three "phases". It doesn't have a separate yellow-green PE. This "shared return" entering the building gets grounded to the central earth point at the base of the building, too. The separate yellow-green PE splits=stems at the base of the building, heading up the whole house.

Now back to earth electrodes. They are implemented at the base of the building deliberately. If you have some natural/inherent large metal object, buried firmly and deep in the ground, there's hardly any point in not using it. As other have pointed out, make sure that your earth tap does not electro-corrode or some such. There are ways to prevent electro-corrosion. And, take care to have the rest of your system in good shape inside and outside the building = well interconnected, the way it should be.

If a lightning does strike, or you have a short to GND from your mains, that's bad luck, but you probably wouldn't avoid harm to your neighbors at large by NOT having our PE system grounded locally to the best available earth electrode :-)

EDIT: Regarding the risk of "hitting your neighbors through the ground water": apparently this is a case of a lesser evil :-) And a matter of making the ground as solid as possible, across an area, so that a fault current doesn't "ruffle its feathers" very much.

A lightning strike, or a mains electricity source, all have a limited energy / current capability. The point of grounding is to conduct any fault current (large but still limited) either back to the source (hence the dedicated return conductor) or into the solid geological earth as directly as possible, so that an elevated voltage doesn't spread through the human-made GND/neutral wiring across the neighborhood, causing damage.

I've recently read an analysis written by someone with decades of practice as a project engineer in high-volt electricity, a transmission line designer who has routed maybe thousands of kilometers of thick wires on pylons at 400+ kV and kiloAmperes of nominal working capacity. That's dozens of kA worth of short circuit capability. For the case at hand, he was debating how far from a "spot of accidental short to earth" there's a dangerous level of "stride voltage", when a wire falls off the pylon, and there's no local earth electrode to the center conductor (which is a dangerous design omission). If memory serves, he mentioned that the dangerous zone had a radius of a couple hundred meters - apparently considering relatively dry soil on the surface.

It has to do with the gradient of voltage (and current) through the mass of the earth, the short circuit current available (or the peak current from a lightning strike) - and a key factor is the soil resistivity. The lower the soil resistivity, the lesser the impact (local elevation of voltage potential) caused by a particular "fault current" level. And, your underground water table improves the "resistance" significantly - unless your geology varies wildly, the underground water soaks a couple dozen miles deep. Electrically that's quite a solid "earth node".

Any fault current hits your in-house PE conductors (lightning collector system) first, reaches the local earth electrode, and spreads into the geology. If your earth electrode is good, your local "base of the building equipotential busbar" doesn't jump very much (voltage-wise), so the voltage pulse spreading to your neighbors via the mains return cabling isn't very high, and is less likely to harm anyone, in terms of their local voltage difference between the mains GND and their respective local geological earth potential. Even if your water table happens to be a layer (maybe several meters) on a lake of asphalt or some such, a good connection to the water table will ensure that your neigborhood is "all at the same level" in terms of the geological earth potential, so again not very different from the mains return GND... counter-arguments are welcome :-)

Should you attempt to protect your neighbors by not grounding to the earth, this is what happens: any fault current ("charge from above") will find a path of least resistance to a suitable "near earth potential". A short in the mains is likely gonna end up in the neutral return, flowing back to your neighborhood, resulting in a voltage step at your neighbors' premises. A lightning, worth millions of Volts, may appreciate any natural conductor: any pipes that happen to be around, live mains, metallic telco or CaTV lines, a rainwater drain pipe coming down the wall, a nice soot-lined (carbonated) chimney... and can skip distances to your geological earth, so not grounding your mains return node to a local earth won't prevent lightning from hitting that earth anyway :-)

The local in-house connection of mains neutral to local earth works the other way too: if a "GND wobble" comes from your neighbors via the mains return wire, having a solid local earth electrode will "bolt it to ground". To your local earth - leaving no differential voltage between mains return, PE and the local geological electric earth potential.

Maybe I'd like to mention one other fault scenario: consider a three-phase system. You get an accidental short in your house, one phase to the shared neutral/return. This will move the potential of your neutral/return towards the phase where the short has occured. At the same time, your neutral/return potential will move away from the other two live phases - thus causing overvoltage, as percieved by powered devices (loads) in those two other phases. This gets worse if you have loose joints in your 3-phase ground return wiring, towards your upstream transformer. Or maybe your uplink to the transformer is just relatively long and relatively small cross-section, which makes the shared return "GND potential" more negotiable, dependent on load distribution among the phases (individual things powered in your house). A solid local earth electrode will help you with that problem, too. So that's a partial reason why licenced "proof testing techies" here measure not only the resistence of the neutral ground return towards the trafo, but also the earth electrodes.

Solar means DC, possibly above 100V depending on the particulars of your setup. DC is a whole different can of worms. I'm not an expert, but I'd hazard a guess that a solid grounding system is key to safety.

I've actually seen electric-powered systems operated without a PE, and with a floating inner "neutral/return node". I've seen plastic cabinets wired like this, used in the "railway trackside" segment of industrial process control. The people building those systems called them "IT", though I'm not sure this maps well to the taxonomy of TN/TT/IT that can be found in the interwebs. So it was essentially small-signal railway safety control gear, along with communications/signaling. An interesting partial problem happens to be, how to isolate broadband digital communication lines, entering the cabinet, to the desired isolation level (double digit kiloVolts) - if you want to keep using existing metallic wiring, rather than upgrade to fiber optic. These cabinets contain small, self-contained "islands of no connection to earth". The point is to make the gear resilient against incindents involving loose earth (neutral return) in the railway traction power. An electric railway engine guzzles Megawatts of power at 3 to 25 kV of voltage, i.e. currents up to the kA range... I know - not your problem. Apologies for going off topic.

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  • \$\begingroup\$ This will be PE for internal connections only. The expectation is that current will travel towards the Electricity Pole's Ground and back to transformer to close the loop. The Neutral coming with Main is usually grounded. For lightening arrester, I cannot use it. The requirement for lightening arrestor is to dig a 2 meter copper pipe into ground, which is being arranged with Municipality (since it next to outer wall on street). I won't be able to interconnect the two Earthing. It is a small house, and the only reason they need two PE now is due to installation of Solar Grid Tie Inverter. \$\endgroup\$
    – Abu Zaid
    Nov 4, 2021 at 18:38
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    \$\begingroup\$ Normal working return=neutral does/should indeed connect to the electricity pole's 3-phase neutral. But, for various saety-related reasons, all your PE in the house should ultimately connect to a single central point, also bolted to your aforementioned mains return (going to the pole) and to any earth electrodes that you happen to have about the house. All the grounds should be one. If you leave them separate into two or more "island", this has adverse safety implications. If I may suggest, routing an extra 10mm^2 yellow-green wire is not that much trouble? \$\endgroup\$
    – frr
    Nov 5, 2021 at 6:33
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    \$\begingroup\$ It may seem counter-intuitive, how a solid earth potential near by can protect you from shock. Quite the opposite should be true, right? If I understand correctly, the solid earth won't protect someone who is standing on one and touches a live wire - but should prevent the dangerous potential from spreading through random/accidenal conductors far and wide, reach neighbors in a broad area etc. Such as, if you have all your water and gas pipes properly earthed everywhere, and you get an accidental short from electric live to some water/gas pipe, the dangerous voltage doesn't spread further. \$\endgroup\$
    – frr
    Nov 5, 2021 at 6:45
  • \$\begingroup\$ Understood, thank you for taking the time to educate me, appreciate it very much. \$\endgroup\$
    – Abu Zaid
    Nov 5, 2021 at 8:27
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That is the best solution. 100 feet into the ground is far deeper than necessary. Googling immediately finds "The electrical code states that it must have 8 feet (2.4 m) of contact with the ground". It sounds right, though I did not followed the source.

Electrocution should not happen, since the whole point of earthing is to prevent electrocution by passing leakage to the earth, which is the reference voltage where you are standing on. Leakage has to be prevented first anyway.

Meantime, it is regular practice to ground to plumbing pipes or a short rode near power mains.

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    \$\begingroup\$ About your last sentence, I would specify that when you connect a ground wire to plumbing it should be done to ground the plumbing itself, not to use the plumbing as ground. \$\endgroup\$ Nov 4, 2021 at 16:19
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    \$\begingroup\$ --1 @AbuZaid It should not cause electrocution as a grounding rode does not. You are not planing to use the earth as a mains current carrying path. What you worried is if there are any electrical path to other places. That is possible if the lightning hits right on your ground. That case, current will find path anyway. Without earthing, the lightning will harm more but not less. I said the best solution you have, that cannot be replaced with anything else. If a inspector has to argue with only what he knows, fire him and get more knowledgeable ones. I have been in may country many town, \$\endgroup\$
    – jay
    Nov 4, 2021 at 18:38
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    \$\begingroup\$ --2 I have been in may countries many towns, not seen any place complaining earthing with plumbing lines. You cannot create enough potential to earth that can affect your neighbors, unless you create an evil genius villain weapon. \$\endgroup\$
    – jay
    Nov 4, 2021 at 18:43
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    \$\begingroup\$ @jay thank you for answer and explanation. The building never had any earthing, and the only reason they are going for it now is because of Grid Tie Solar Inverter installation, where Grounding is a requirement. Since it passed resistance test, I have approval by the Inspectors. My only concern was depth of pipes, as it reaches underground water and I wasn't sure if it will cause any harm. Appreciate you taking the time to answer my questions, I have upvoted your answer, but since I can only accept one answer, I will accept frr's answer due to details he provided. \$\endgroup\$
    – Abu Zaid
    Nov 4, 2021 at 18:51
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    \$\begingroup\$ @AbuZaid no problemo. I am just happy to see someone gets relief. :) \$\endgroup\$
    – jay
    Nov 4, 2021 at 18:55

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