Earthing mains power supply - Page 1
Forum section: electronics / projects

author: akis
author_rank: Frequent Contributor
timestamp: June 25, 2020, 02:32:39 pm
content: The ground wires in my house all go to the consumer unit (main fuse box) and there they connect to the Neutral of the incoming mains power supply. In other words my "earth" is the neutral of the mains.My question is, if there are buried copper pipes or other physically grounded devices can this create some problem? because then it seems I have two "earths", one underground and another the neutral of the incoming mains supply which I presume is connected to the Earth at the substation?

author: themadhippy
author_rank: Super Contributor
timestamp: June 25, 2020, 03:01:45 pm
content: Quotesounds like you have a TNC-S supply arrangement,or pme in old money,about the most common in the uk,Tera or earth and Neutral are Combined on the incoming supply and Separate on the consumer side.Quoteyes you can get a potential between your electrical earth and mother earth, "equipotental bonding"is the answer.Or in other words ,connecting the services (gas a water etc) entering your property to your main earth terminal so there all at the same potential as the electrical earth .Also the supply cable often has the neutral/earth spiked to earth to keep the potential lowish

author: bjbb
author_rank: Contributor
timestamp: June 25, 2020, 03:11:37 pm
content: Perhaps it is TN-C-S. Depends on the distribution system particular to your region. Hi-Z earthing to the distribution transformer is not unusual for parts of the UK.Seehttps://en.wikipedia.org/wiki/Earthing_system;and reference regulation 411.3.1.2 and BS7671

author: akis
author_rank: Frequent Contributor
timestamp: June 25, 2020, 03:30:59 pm
content: Alright, so if my house's earth wires solely depend on the incoming mains supply neutral for earthing purposes, there can potentially be an impedance in that leg from faulty electrical device chassis to the real Earth travelling for miles maybe before it connects to (mother) Earth. Is it not then better to have a few rods into the ground (or buried copper pipes, or basement swimming pools etc) to make sure that my earth wires have a very short and very low impedance path to Earth?Ah just saw this"Also the supply cable often has the neutral/earth spiked to earth to keep the potential lowish"Yes, that is what I am saying would be prudent, but do not have it at my house.Can I just install my own iron rod into the ground? Will I be breaking any rules?

author: themadhippy
author_rank: Super Contributor
timestamp: June 25, 2020, 04:08:14 pm
content: Quoteyes,maybe,no,it all depends who you ask.

author: Monkeh
author_rank: Super Contributor
timestamp: June 25, 2020, 05:13:00 pm
content: Quote from: akis on June 25, 2020, 03:30:59 pmWhat's 'the real earth'? You want the current to return to the other leg of the supply when there's a fault. A TN-C-S setup is pretty much ideal for this - your CPC ('earth') provides a return path all the way back to the supplier via the combined neutral/earth conductor. The 'mother earth' is the centre tap of a three-phase transformer likely within a few hundred metres of you, connected to you by some very large, very low impedance cables.QuoteAs far as the electrical installation is concerned, they already do. As far as the potential of the ground under your feet, you're not likely to achieve less than a hundred ohms with a rod.

author: themadhippy
author_rank: Super Contributor
timestamp: June 25, 2020, 05:25:08 pm
content: one of the problems with any tnc type supply is if the neutral earth bond goes missing at the sub station,the return current will travel by any route it can to earth,if you have extra rods installed giving a nice low impedance path to earth the majority of the return currents for the network may end up with you.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 27, 2020, 08:19:26 am
content: Why would you even bother to think about this?Curiosity and wanting to know things is good of course, but is there any problem that needs "fixing"?I have some memories of pipes for other utilities (water, gas, etc) may not be used anymore (in some area's of the world) for earth grounding because they are not "designed" for it. Some people have been electrocuted because of faulty grounding after metal pipes have been replaced with plastic pipes, so instead of blowing a fuse in the case of an electrical fault, your bath or other stuff gets live.In these modern times an RCD seems a more sensible option:https://en.wikipedia.org/wiki/Residual-current_device

author: akis
author_rank: Frequent Contributor
timestamp: June 27, 2020, 04:37:49 pm
content: "Why would you even bother to think about this?"Installing an electricity kiosk at the edge of my land where the incoming supply and the meter will go. I asked the electrician what we do about grounding.and he said "nothing", so then I asked here in order to learn.Subsequently, the electrician brought another electrician over for advice, who said we need to place two grounding rods into the ground, one next to the kiosk and one next to the property, some 35 m away.I have now asked a 3rd electrician and am awaiting his reply as to how we need to go about this.

author: Monkeh
author_rank: Super Contributor
timestamp: June 27, 2020, 04:44:05 pm
content: Okay, so you're moving the cutout away from the building.What's the supply type?

author: themadhippy
author_rank: Super Contributor
timestamp: June 27, 2020, 05:02:04 pm
content: If i was doing the job i wouldn't take an earth or put a rod in at the kiosk keeping it a true TN-C-S within the kiosk and make the supply at the property a TT system.If using swa to connect from the kiosk to property only connect the armouring at the supply end.

author: akis
author_rank: Frequent Contributor
timestamp: June 27, 2020, 05:42:39 pm
content: Quote from: Monkeh on June 27, 2020, 04:44:05 pmI think it is live in the centre and neutral on the steel armour, but cannot be sure.

author: Monkeh
author_rank: Super Contributor
timestamp: June 27, 2020, 05:47:30 pm
content: Quote from: akis on June 27, 2020, 05:42:39 pmWell, you'd need to ask the DNO.. they probably aren't using steel armour for that matter.If you have a TN-C-S supply I see no problem whatsoever with simply carrying that on to your building and performing bonding as normal. No need to TT, no rods, just use the supply normally.

author: themadhippy
author_rank: Super Contributor
timestamp: June 27, 2020, 06:53:59 pm
content: QuoteDepends how you interpret the regs regarding extending TNCS outside the equipotenial zone,and whats regarded as the zone.

author: Monkeh
author_rank: Super Contributor
timestamp: June 27, 2020, 07:00:02 pm
content: Quote from: themadhippy on June 27, 2020, 06:53:59 pmWell, there's absolutely no need to have any exposed metal whatsoever at the site of the cutout, which means there is no zone to care about.But yes, the joys of equipotential zones, bonding, and exporting are real.. Remember radiator clamps? Some serious re-evaluation of that bit of The Book is needed. Again. Let's bring up car chargers for more hilarity.

author: themadhippy
author_rank: Super Contributor
timestamp: June 27, 2020, 07:56:40 pm
content: QuoteI'll see your radiator clamps and raise with bonding metal window frames in the bathroom.

author: akis
author_rank: Frequent Contributor
timestamp: June 28, 2020, 07:22:59 am
content: "I'll see your radiator clamps and raise with bonding metal window frames in the bathroom."If I understand correctly you are saying that one should only earth an electrical device that has a chance of exposing its live power to its metal chassis, but one should not earth a passive device like a radiator?

author: ocset
author_rank: Super Contributor
timestamp: June 28, 2020, 12:17:40 pm
content: good to ask here, to get the more theoretical viewpoint.But i am sure you have asked here aswell..https://www.electriciansforums.net/The radiator doesnt need to be earthed, but it wont be harmful to do so.Unless you can draw a schem of some danger situation with your earthing method, then its fine.I cant see any possible danger of any of the situations you have described.I presume you have an RCD in that part of the wiring that goes back to the earth/neutral junction?Even with a wiring system thats not earthed, and use of severely dangerous kit, it can be hard to shock yourself...as you see here at 7:30Here is the first part of thisHowever, i absolutely recomend not doing this and only using electricians standards in wiring.Millions of households in Brazil for example, dont have any earth connection or any earth wiring, and there are few if any reports of accidents.

author: themadhippy
author_rank: Super Contributor
timestamp: June 28, 2020, 12:51:41 pm
content: QuoteNo i was responding to Monkeh's comment about the days in reg gone past were the whole earth bonding was starting to get silly. Sense has,at last,started to prevail and as long as certain other regs are met theirs no need to be knitting every bit of metal or pipework together with electric string.

author: ocset
author_rank: Super Contributor
timestamp: June 28, 2020, 01:03:32 pm
content: QuoteYes, this is the bad situation, if neutral and earth are not connected at the sub-station due to some fault there...however, this will result in dangerously high mains live voltages which will result in blown MOVs in many mains plugged devices in your house, and your house supply fuse would likely blow.Im pretty certain most house electrical junction boxes have mains voltage detectors in them which switch off the supply if it goes too high in voltage.

author: Monkeh
author_rank: Super Contributor
timestamp: June 28, 2020, 01:19:11 pm
content: Quote from: treez on June 28, 2020, 01:03:32 pmtreez, you have absolutely no idea what you're talking about.

author: David Hess
author_rank: Super Contributor
timestamp: June 28, 2020, 09:31:45 pm
content: Where I live not far from St. Louis, Missouri, several houses in a row along the power distribution lines use the same pole transformer and each of them has their own ground rod connected to neutral at their primary distribution box so there are several ground rods tied to the same neutral over hundreds of yards. The areas in California where I have lived did exactly the same thing.When I installed several chimney mount antennas, I considered the existing power ground rod completely inadequate for lighting protection so I installed my own 10 foot length of 1/2" copper pipe at the base of the chimney and filled it with salt. (1) Where I have seen shacks for radio gear at the base of antenna towers, they did the same at every corner of the shack while tying the rods all together.(1) Use a fitting to attach a garden hose to the top of the pipe and use water pressure to hydraulically drill it into the ground. This is much easier than pounding on it.

author: ocset
author_rank: Super Contributor
timestamp: June 28, 2020, 11:00:13 pm
content: QuoteWoops yes sorry, I was thinking of a lost neutral conductor in a 3 phase system (as you know all domestic mains originates from 3 phase at some point)…….the consequences of a lost neutral conductor will vary, depending mainly on the load balance conditions in the three phase system, but also on the type of earthing system used and the position of the break in the neutral relative to the load.Worst case scenarios could include both damage to connected loads due to overvoltages on single phase circuits or the creation of hazardous touch voltages on exposed conductive parts.

author: Bassman59
author_rank: Super Contributor
timestamp: June 29, 2020, 04:43:53 am
content: Quote from: akis on June 28, 2020, 07:22:59 amI read it as radiators (and the metal window frames) are a sufficient ground, rather than a proper ground going back to the panel.

author: Monkeh
author_rank: Super Contributor
timestamp: June 29, 2020, 04:47:14 am
content: Quote from: Bassman59 on June 29, 2020, 04:43:53 am.. no, they're absolutely not.There was some minor insanity regarding bonding every metal object you could possibly touch to earth. It was, indeed, insanity, and we now only concern ourselves with objects capable of introducing a (sufficiently low impedance) potential.

author: ocset
author_rank: Super Contributor
timestamp: July 01, 2020, 10:52:06 am
content: The neutral and earth should not connect in the consumer unit, only the network operator is allowed to connect them in the service terminal equipment (head) to create a TN-C-S system.But as the earth is already tied to the neutral, TNC-S, then it is a good bet that this will not change. I cannot see any need for additional earth electrodes unless a car charging point, or similar, is being added.

author: themadhippy
author_rank: Super Contributor
timestamp: July 07, 2020, 02:49:55 am
content: QuoteThere is a very rare beasty called TNC were neutral and earth are combined on the consumers side.Its also known as concentric earthing as the earth/neutral conductor must surround the phase conductor.Ive only seen 1 example in the wild and that was a long time ago.

author: Zero999
author_rank: Super Contributor
timestamp: July 07, 2020, 09:06:40 am
content: Quote from: Monkeh on June 29, 2020, 04:47:14 amThe UK wiring regulations are like that: pretty much all metalwork in a building needs to be bonded to earth.

author: themadhippy
author_rank: Super Contributor
timestamp: July 07, 2020, 01:33:24 pm
content: QuoteNot necessarily so anymorehttps://electrical.theiet.org/wiring-matters/years/2019/76-july-2019/protective-bonding-habits/