A broken PEN can result in significant ( destructive ) overvolting of supplies that are connected to broken PEN
-
Looking for a smarter way to manage your heating this winter? We’ve been testing the new Aqara Radiator Thermostat W600 to see how quiet, accurate and easy it is to use around the home. Click here read our review.
Do I need an Earth Rod Fitted?
- Thread starter richards1978
- Start date
A broken PEN can result in significant ( destructive ) overvolting of supplies that are connected to broken PEN
Yes, I know that - but, as I said, I thought (maybe wrongly?) that the 'most common situation' would be under-voltage.
What your diagram does not show is the (very likely, and potentially low impedance) paths from the isolated section of PEN and true earth, through bonding conductors and extraneous-c-ps (or even a deliberate earth electrode).
That is also my understanding - so why did you write (my emboldening) ...
?
- Joined
- 27 Jan 2008
- Messages
- 27,409
- Reaction score
- 3,310
- Location
- Llanfair Caereinion, Nr Welshpool
- Country
PME the ME stands for multiple earths, TN-C-S as pointed out may not have multiple earths, it is near impossible to know if a supply is TN-S as the heads can look the same.
By fitting multiple earths, should we get a broken PEN, then the voltage swings will be reduced, but one will be getting a current through the earth rod, and one would not want too much current to flow, or it could melt the earth wire connecting it, but that would require a very good earth, and unless you're a radio ham, the chance of having an earth that good is very unlikely.
So you will still get voltage swings both under and over voltage should one lose the PEN. The EV charger has caused more concern about loss of PEN this video
talks about the problems, I would think this will go over the head of most people, the problem is we are seeing homes using both more and less power today with solar panels, heat pumps, and EV charging points.
So years ago most homes used around the same amount of power, so the voltage swing would not have been that much. But today we can use both more and less to just a few years ago, and we need protection against two earths which are not the same voltage once we leave the equal potential zone formed by bonding within the home, so we are seeing earth rods being fitted as a reference and as an independent earth when we have an uninterruptible supply from the likes of solar panels and batteries or charging EV's outdoors.
But when there are no EV points, batteries, or solar panels, then the DNO provided earth is considered good enough.
By fitting multiple earths, should we get a broken PEN, then the voltage swings will be reduced, but one will be getting a current through the earth rod, and one would not want too much current to flow, or it could melt the earth wire connecting it, but that would require a very good earth, and unless you're a radio ham, the chance of having an earth that good is very unlikely.
So you will still get voltage swings both under and over voltage should one lose the PEN. The EV charger has caused more concern about loss of PEN this video
So years ago most homes used around the same amount of power, so the voltage swing would not have been that much. But today we can use both more and less to just a few years ago, and we need protection against two earths which are not the same voltage once we leave the equal potential zone formed by bonding within the home, so we are seeing earth rods being fitted as a reference and as an independent earth when we have an uninterruptible supply from the likes of solar panels and batteries or charging EV's outdoors.
But when there are no EV points, batteries, or solar panels, then the DNO provided earth is considered good enough.
No. Standard procedure, and why TN-S doesn't really exist any more.
Yes, but as I've said, it is not 'allowed' to configure an installation as TN-C-S (i.e. have the installation's 'earth' derived from the neutral at the cutout) if the supply distribution circuit has not been PMEd.
Surely not "will be reduced", but, rather, "may be reduced" - since it all depends upon where the PEN is 'broken'?
The "ME"s of PME are surely the DNO's ones, not those provided by any customer (whether radio ham or not)?
Your installation is presumably still configured as TN-S - i.e. your 'earth' is derived from the sheath of the cable that enters your property?
That being the case, I would think that they have not done anything particularly (electrically) dodgy (at least for the time being) provided that the cable sheaths are intact (and of adequate low impedance) between their new downstream joint and your property - but I can't see how they could be sure that such is the case unless they undertook measurements in your house.
If they reconfigured the wiring within your house to derive your 'earth' from the incoming 'neutral' then, as flameport implies, they would then effectively have made the whole thing TN-C-S (which means that they also should have also PMEd it.
- Joined
- 18 Apr 2022
- Messages
- 4,434
- Reaction score
- 525
- Country
Because they've compromised it as per what they did in my street?
Yup.
They didn't.
1) My earth remains as it was, and as it was when originally installed decades before TN-C-S started to be used.
2) As far as I could see they did not install an earth rod at the location of the repair.
What they did has to have been going from this:
to this:
Whether upstream or downstream of my house I do not know. But my road is a cul-de-sac, so the cable must run up one side, around the end, and back down the other side, and several years ago they did a repair on the other side of the road, more or less opposite this one, so if they did the same then what I now have must be this:
As I wrote, provided only that the cable sheath is intact/satisfactory from where it is connected to the neutral to your house (and your installations earth has always been dependent upon that) then, providing the cable has been PMEd (see below) then what you now have would seem to effectively be a perfectly satisfactory TN-C-S earth (even if achieved in a slightly unconventional manner) - so, if I were you, I don't think I would have any concerns, other than about the health of the cable sheath on which I was relying (but that has always been something to 'be concerned about', even before the DNO's 'repair')..
As I presumed/expected.
There only has to be one earth rod (somewhere) in addition to the one at the transformer for it to qualify as PME. I had previously always 'assumed' that the 'M' of PME usually meant 'several', but the late-lamented westie used to tell us that when a distribution run was PMEd (to facilitate TNC-S) DNOs commonly only installed one extra rod, usually at the end of the cable run.
Yes, I understood that to be what you were describing
In commenting on this I may be "sticking my neck out " - again.
However, may I bring to your attention (once again) the Mike Holt video
While this (lengthy) video refers to the TN-C-S system used in North America (and Australia),
it should be noted that Grounding/Earthing serves two separate purposes.
System Grounding
and
Equipment Grounding.
(it seems (to me) that the discussions, so far, have related to Equipment Grounding/Earthing
but
not System Groundling/Earthing.)
These are discussed in this video, starting at 21:00
and the reasons for System Grounding are discussed starting at 23:00.
Note that at (at 27:00) he states
"The (System) Grounding Electrode conductors shouldn't be any longer than necessary and unnecessary bends and loops should be avoided"
- to ensure minimum IMPEDANCE.
Also note that (at 31:30) with an "outbuilding",
an additional Grounding Electrode (not there connected to the Neutral) is required
so that the System Grounding electrical conductor is as short as possible and, hence, of low impedance.
Equipment Grounding is discussed, starting at 28:30.
Equipment Grounding/Earthing is actually connecting the exterior conductive materials enclosing equipment (via a Protective Earth conductor)
to the NEUTRAL - which is also connected to Ground Earth (at ONE point), which is why it is called the Neutral.
See https://commons.wikimedia.org/wiki/File:TN-S-earthing-EN-v2.svg
The length (and inductive impedance) of this PE "Path" is not important for Equipment Grounding, as long as it of relatively LOW resistance,
so that - under fault conditions - a high current can flow to operate the "Breaker" (or fuse in a BS 1363 plug)
and disconnect the circuit.
https://commons.wikimedia.org/wiki/File:HomeEarthRodAustralia1.jpg
shows a System Grounding connection which is the complete anthesis of the manner in which the conductor should be "run".
Both System Grounding and Equipment Grounding are applicable to all Grounding/Earthing systems.
Last edited:
If two phases are involved then as per the diagram one house will be undervolted while the other house will be over volted.
If the isolated section of PEN has no path to Ground then the two houses will be in series across a 400 Volt ( 2 phase ) supply.
- Joined
- 27 Jan 2008
- Messages
- 27,409
- Reaction score
- 3,310
- Location
- Llanfair Caereinion, Nr Welshpool
- Country
I have seen it only once where the homeowners earth caused a problem, and it did save him losing any equipment other than the earth wire to his shack, he had 4 earth rods, one each corner of his garden, and earth tape between them for his transmitting equipment, and the electrician wiring his shack had bonded his earth bar for the radios, this was you must admit an extreme case.
In the main earth rods are around 60Ω so 230/60 = 3.8 amps which is not going to damage the earth wire, and also unlikely to make much difference with loss of PEN.
There was a suggestion some years ago that all homes should have an earth rod, but this was dropped, the problem is where two earth systems are in proximity, so someone could touch both simultaneously, since most houses are made of a non-conducting material, i.e. bricks, touching the walls of a house and true ground is not a problem.
With caravan like structures where they have metal walls, the use of TN-C-S is banned, by ESQCR as to how we get away with TN-C-S supplies to cars, I don't know, I suppose you can't get EV motor caravans as you would not know where they can be charged.
But proximity of street furniture where the earthing system is unknown is a problem.
Also, in the case of an island of homes, where a damaged supply cable may not cause all devices to disconnect, the out of voltage range and frequency is used to tell devices to disconnect, but where there are many devices, ensuring they don't take turn in disconnecting is not easy, it is hoped that they disconnect fast enough, so no device tries to reconnect.
It seems 50 volts AC is considered as the safe limit unless it comes from an EV then allowed 75 volts, I have not worked out the thinking behind that?
Same as 6 mA DC with RCD's, with an EV charging point with auto disconnection if over 6 mA yes, but rest of the circuits in a house do not have that disconnection device, and we have had DC on the mains supplies for years, the simple three port valves, used with central heating, for example.
I am sure the old CRT TV's with resistors to drop the volts also caused DC.
The rule books don't help, "Existing installations that have been installed in accordance with earlier editions of the Regulations may not comply with this edition in every respect. This does not necessarily mean that they are unsafe for continued use or require upgrading." The "necessarily" is the word we look at, so pre-1966 we could have a "Lighting fittings using filament lamps" without an earth, but getting filament lamps today is not easy, there were also other provisions, like "mounted at such a height that they cannot readily be touched" so wall lamps still needed an earth.
For a time, we changed the coding with EICR as it was felt the "does not comply with current edition" was confusing to the owner, so we moved to dangerous and potentially dangerous, how any 230 volts supply can not be potentially dangerous I have not worked out?
And a RCD does not stop you getting a shock, it only reduces the time you can get a shock for, hence not primary protection, so should not being fitted really mean a code C2? Don't get me wrong, I think they should be fitted, but we are leaving too much to how an inspector reads the rules and what he considers as potentially dangerous.
The problem is, the homeowner often does not have a clue how potentially dangerous anything is, we see a report with a C2 and often not even a location for the fault, never mind what is the inspector's concern, and some faults I have hunted to see what he has looked at as being potentially dangerous, and have failed, if I have failed, what chance has the homeowner?
In conclusion, a DNO TN supply does not need an earth rod.
OK, there are specials, like my house, because I have solar and batteries which can provide an uninterruptible supply to my freezers and central heating, even with a loss of the DNO supply, but after all my waffling on, the simple answer is a DNO TN supply does not need an earth rod.
When I lose the DNO supply and use my own generating system then I need an earth rod, but not until that happens.
In the main earth rods are around 60Ω so 230/60 = 3.8 amps which is not going to damage the earth wire, and also unlikely to make much difference with loss of PEN.
There was a suggestion some years ago that all homes should have an earth rod, but this was dropped, the problem is where two earth systems are in proximity, so someone could touch both simultaneously, since most houses are made of a non-conducting material, i.e. bricks, touching the walls of a house and true ground is not a problem.
With caravan like structures where they have metal walls, the use of TN-C-S is banned, by ESQCR as to how we get away with TN-C-S supplies to cars, I don't know, I suppose you can't get EV motor caravans as you would not know where they can be charged.
But proximity of street furniture where the earthing system is unknown is a problem.
Also, in the case of an island of homes, where a damaged supply cable may not cause all devices to disconnect, the out of voltage range and frequency is used to tell devices to disconnect, but where there are many devices, ensuring they don't take turn in disconnecting is not easy, it is hoped that they disconnect fast enough, so no device tries to reconnect.
It seems 50 volts AC is considered as the safe limit unless it comes from an EV then allowed 75 volts, I have not worked out the thinking behind that?
Same as 6 mA DC with RCD's, with an EV charging point with auto disconnection if over 6 mA yes, but rest of the circuits in a house do not have that disconnection device, and we have had DC on the mains supplies for years, the simple three port valves, used with central heating, for example.
I am sure the old CRT TV's with resistors to drop the volts also caused DC.
The rule books don't help, "Existing installations that have been installed in accordance with earlier editions of the Regulations may not comply with this edition in every respect. This does not necessarily mean that they are unsafe for continued use or require upgrading." The "necessarily" is the word we look at, so pre-1966 we could have a "Lighting fittings using filament lamps" without an earth, but getting filament lamps today is not easy, there were also other provisions, like "mounted at such a height that they cannot readily be touched" so wall lamps still needed an earth.
For a time, we changed the coding with EICR as it was felt the "does not comply with current edition" was confusing to the owner, so we moved to dangerous and potentially dangerous, how any 230 volts supply can not be potentially dangerous I have not worked out?
And a RCD does not stop you getting a shock, it only reduces the time you can get a shock for, hence not primary protection, so should not being fitted really mean a code C2? Don't get me wrong, I think they should be fitted, but we are leaving too much to how an inspector reads the rules and what he considers as potentially dangerous.
The problem is, the homeowner often does not have a clue how potentially dangerous anything is, we see a report with a C2 and often not even a location for the fault, never mind what is the inspector's concern, and some faults I have hunted to see what he has looked at as being potentially dangerous, and have failed, if I have failed, what chance has the homeowner?
In conclusion, a DNO TN supply does not need an earth rod.
OK, there are specials, like my house, because I have solar and batteries which can provide an uninterruptible supply to my freezers and central heating, even with a loss of the DNO supply, but after all my waffling on, the simple answer is a DNO TN supply does not need an earth rod.
When I lose the DNO supply and use my own generating system then I need an earth rod, but not until that happens.
Compromised, converted, altered, changed, whatever.
Either way, such repairs have been going on for decades and can be found everywhere.
Cable with 3 inner cores for the phases and the outer is the CNE.
TN-S is not TN-S unless you can see all of the cable between the transformer and the electrical installation.
In the vast majority of installations that is not possible.
should that not be something like:
After all, TN-S is TN-S (as a simple fact) and that surely remains true even if one cannot see that it is?
DIYnot Local
Staff member
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local
