When we moved into our 1930s house 12 years ago we had a fair amount of electrical work done, including a new supply fuse, main switch and consumer unit. See picture. According to the certificate the set-up is TN-C-S, earthed on the 'distributor's facility' and you can see the earth wire running down to the block on the side of the supply fuse (which is 3-phase, as our house has a three phase incoming cable, although we only use a single phase). Outside in the flower bed is the old earth rod - a hangover, I vaguely remember the electrician telling me, from the previous installation - but back in 2010 it was not removed and the original thin cable runs from it runs into the CU, although you can't really see it in the picture as it runs behind the main switch and meter. The other day while gardening I noticed that it had become disconnected from the top of the earth rod which sits about 4inches above ground level. Not unduly worried, I simply reconnected it into the chunky screw clamp, but is it normal to retain a legacy earth rod on a TN-C-S system? Does it do anything given the 'certified' earth is on the supply head?
TN-C-S and an Earth Rod?
- Thread starter Nilly
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Ok.
I don't know if 'normal' is the right word.
W e l l - it could be useful in rare faults with the TN-C-S Neutral(earth).
Earth rods and other types are not 'legacy', they are vital parts of electrical infrastructure.
Historically most properties in the UK have not bothered with them, relying only on the supplier provided earth terminal. This is because until recently, installing one was not required or even suggested in most cases.
Earth electrodes are now recommended for TN installations, as stated in BS7671, 411.4.2
Most other countries have required earth electrodes for all installations for many decades.
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In theory most supplies are PME, the ME stands for multiple earths and the DNO (supplier) was supposed to fit many earths, maybe not rods, but still multiple earths, however seems they got lazy, and renamed it TN-C-S and have not fitted as many earths as they use to, so the user has been advised to fit them instead, and with solar panels, and the possibility of running as an island, we need earth rods anyway.
However, when mine was fitted the guy fitting it showed me his meter, showing less than one ohm, I think that is extremely unlikely, so do not really want to trust it.
However, when mine was fitted the guy fitting it showed me his meter, showing less than one ohm, I think that is extremely unlikely, so do not really want to trust it.
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Historically the Earth was very often the metallic water supply pipe.
I would suggest you get some basic tests conducted by a competent spark with proper test kit
Yup, pretty much as Flameport has said.
Earth rods are generally a good idea and does not hurt to have one and could even prove vital in some instances.
Extremely unlikely to make a small impedance earth fault path.
Two things that have made their use more vital.
1/ Suppliers are allowed to use one conductor for both N & E theses days, including parts of "TNS" supplies therefore making it very TNC-S like to nearby supplies.
2/ Getting rid of metal gas and water pipes in the supply infrastructure - in years gone by they used to act as if a massive earth earth rod/mat type system - no longer these days, fortuitous yes but very effective in many cases.
So, having an earth rod or three is usually a good idea if firmly bolted to the Main Earth Terminal or thereabouts.
Earth rods are generally a good idea and does not hurt to have one and could even prove vital in some instances.
Extremely unlikely to make a small impedance earth fault path.
Two things that have made their use more vital.
1/ Suppliers are allowed to use one conductor for both N & E theses days, including parts of "TNS" supplies therefore making it very TNC-S like to nearby supplies.
2/ Getting rid of metal gas and water pipes in the supply infrastructure - in years gone by they used to act as if a massive earth earth rod/mat type system - no longer these days, fortuitous yes but very effective in many cases.
So, having an earth rod or three is usually a good idea if firmly bolted to the Main Earth Terminal or thereabouts.
As you surely know, PME and TN-C-S refer to two totally different things.
In the UK, one can only have TN-C-S if there is PME but, the other way around, there are probably millions of installations (mine for one
) which have a PMEd supply but are not TN-C-S. So it is totally wrong to suggest that anyone "renamed PME" to "TN-C-=S".It does - but I was pretty disillusioned when the late-lamented Westie told us that the "M" was very often just "two" - one at the DNO's transformer and the other at the end of the DNOs distribution cable run.
There is also a PNB variant of TN-C-S in what is often termed the "UK".As you surely know, PME and TN-C-S refer to two totally different things.
In the UK, one can only have TN-C-S if there is PME but, the other way around, there are probably millions of installations (mine for one
It does - but I was pretty disillusioned when the late-lamented Westie told us that the "M" was very often just "two" - one at the DNO's transformer and the other at the end of the DNOs distribution cable run.
As I understand it, PNB only really differs from PME when an installation is the only one fed from a DNO transformer (an unusual situation for domestic installations in UK), the one N-E connection (other than the one at the transformer being at, or very close to, the installation.
If multiple installations share the same feed from a transformer then, since the N is common to them all, the N-E connections, at, or close to, each of those installations amount to 'PME', don't they?
PNB will be supplying a single customer.
That's what I said - and, as I also said, that is a very unusual situation for a domestic installation in the UK.
Also, given what westie told us, if there is just one customer and the N-E connection is at the end of that single run of cable (i.e. at the installation), then it would actually seemingly qualify as PME!
There are two types of "Earthing"
"System Earthing" and "Equipment Earthing"
Connecting the PE Conductor at the premised to the Neutral - connected to the "'certified' earth is on the supply head" - provides Equipment Earthing.
Without the "Earthing Electrode" - in the Garden - "System Earthing" is likely to be relatively ineffective.
This may not much matter if you are in a bult-up area, as you must be.
This is because "System Earthing" is to protect against "surges" caused by relatively close electrical discharges, such as "Lightning Events".
In a built up area it is likely that "Lightning Events" would mostly be taken by much higher objects and Power distribution facilities (Poles and Wires).
Although it is of US origin and the term "Grounding" is used, the following (long) video explains much concerning Earthing of electrical systems.
particularly from 25:50 to 28:50.
After watching the above particular section, you should see that the "electrician" who installed the following did not understand that which he was doing.
File:HomeEarthRodAustralia1.jpg - Wikimedia Commons
Maybe it's just me (and, as you know, I'm not an electrician) but I don't think that those terms are very familiar to those in the UK.
I would also think that "equipment earthing" is a pretty misleading term, since the primary purpose of what you are describing as 'equipment earthing' is surely the protection of human beings (and other animals), rather than 'equipment, isn't it?
Again, this is something which, in the UK seems usually to be considered separately from the 'earthing' of an electrical installation.
Searches for these terms gets far more 'hits' for "System Grounding" and "Equipment Grounding" than the corresponding terms using the word "Earthing" - which suggests that these terms/concepts may be more familiar in the US>
No they are not John, you are correct.
Earthing is what we do at the supply, whether from the supplier or own earth rod/plate et etc and it relies on the Earthing principle.
Bonding is what we do to join things together to equalise the potential.
Main Bonding we , not long ago, named EEBADS or Earthed Equipotential Bonding Disconnection of Supply.
We were told there is no such term as "Earth Bonding" but I do not quite agree with that in reference to main bonding.
If we have two or more "Earth Sources" in a supply they must be joined together - Electrical Earth (However Derived), Pipework etc and Earth Rods/plates etc.
So if you have an Earth Rod etc you must robustly join it to your Main Earth (System earth if you like), so all Earths then are pretty much the same Potential (Voltage) .
You Electrical Earth from your supplier can be example 35V adrift from the soil beneath your feet, so bonding pipework etc that runs thru it to your electrical earth helps keep them all together at whatever voltage they are compared to the End of the Universe (Well the Planet Earth really).
One reason these "Earths" might be at different voltages is if heavy industry is close, other (more temporary) differences occur in lightning strikes etc.
Supplementary Bonding does not need go right back to you main earthing terminal but purely to one location - say bathroom example - rather than the whole house.
A Builder Bloke once exclaimed to a few of us "An Earth is an Earth is an Earth" in a matter of fact style.
I replied "Oh No it is not!" .
That standoff lasted a few days.
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