House Earthing TN-S or TT....

[MartinJ]

....TN-S appears outside, butt TT employed inside.

Good Evening Everybody (This is my first post)

Overview:
The supply to my parent's cottage consist of an overhead line of three individual cables. Originally, the supply drop from the final pole to the house also consisted of three cables (remnants of which remain in a seen in an attached photo).
In 1990, the three individual cables from the final pole into the house was replaced by a Split-Concentric cable. Looking at the cutout in the photo, there is a small piece of plastic which 'wobbles' (I know you shouldn't) over where (when I've seen other cutouts the same style) an Earth block is located, whether this cover is meant to simply meant to slide off or not I don't know, but the Consumer Unit is now in the way.
Prior to the new cable being installed the cutout was much further to the left, with the meter to the left of it with the tails from the meter running to a BS3036 CU.
Now, the old cutout was directly below the 3036 CU and after the current incoming cable and cutout (moved much further to the right) was installed I remember an Earth cable (probably 6mm2) dangling from the 3036 CU connected to nothing-although I'm sure there was a 'pinch' mark on it, therefore suggesting it had been connected to something, although far too short to connect to the new cutout should it have been.
My father claimed when the new cable was installed, he mentioned to the DNO people he himself installed an Earth electrode outside when the house was re-wired in the early 1980's, of which one of the DNO people mentioned not to worry about Earthing, as there was one 'on the poles running to the house'.
Anyway, for a few years this is how things remained (Yes I know, the house been without effective Earthing!!!).
Then we required three extra circuits to be installed and had the 3036 CU replaced with a Wylex MCB/RCD CU with 100mA T/D incomer and 30mA for sockets and outside circuits, (16th Edition applied at this time), with the earth rod (apparently not initially required as above) remaining and regarding the RCD protection in use as a TT system.
This how it is to the present day.
BUT the question has always bugged me 'Is this truly meant to be a TN-S system OR a TT system as is currently the present case.

I did enquire about this with photos on another site, but with no definite answer.
Some suggested 'Split-Phase' but I can tell you it is only a 2 bedroom cottage, no storage heaters (never).
Some say overhead TN-S supplies do not exist, but I have when reading on this site had seen people mentioning to have seen them, although a rarity.
If you look carefully at the rear transformer view, you can see a link between the middle and bottom conductors (N-E link?).
The transformer supplies three properties altogether, one set of three conductors leading to a nearby property, and another set of conductors leading to a pole which in turn supplies to other properties, including my parents.
On a side note, two properties fed from this transformer are right nearby, whilst the supply to my parents is a very long overhead supply (if this is actually a TN-S Earth, if a RF Circuit was protected by a 30A 3036 fuse as was originally the case, how long would it take to rupture and disconnect in an Earth fault with such a very long, thin overhead line?)
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Problems with uploading photos, could someone help please?

 

[MartinJ]

Without a picture I cannot be certain that the cutout you have is the same as I think it is, and I'm not going to advise any further in case I am wrong and you put yourself in danger by attempting to follow my incorrect advice.
That must be a very old book as the electricity boards haven't existed for around 40 years now, electricians can make that connection these days.

If the customer said that they didn't want to be connected to the suppliers earth then that is their choice, it sounds like this is the case from your OP.
The covers were left in place whenever the earth connection wasn't to be used, either due to it being unsuitable or there being nothing there to connect to it. The cover has knockouts so it could be replaced after the electricity board operative made an earth connection. These days the electrician will often make that connection.

The suitability of the earth can only be established by enquiry with the DNO and by testing it.

If it is the type of cutout I think it is then the earth terminal cover can be removed even with a CU tight up against it.

HI
Just thought I would add some more photos of the cutout I have just taken.
There is also a short video of the Earth block cover wobbling slightly and you can hear it moving as well.
Just to let you know, I certainly did not pull on it or anything, what you see in the video is just gentle movement.
As said earlier, if it is a cover that simply 'slides' off it looks like it will only do so in the left direction, only the CU is against it.

I thought I saw that, but not very clear.

Until a few years ago, the land was Public Footpath area, but since then no longer, otherwise I could have gone and taken a close photograph (one person living down the road got 'told off' by the land owner for walking through it, unaware it had been made private).


If it is working fine then no need to change!

Usually what forces your hand is if a MCB or RCD fails and you find you can't get replacements for an older model and (of course) the busbar arrangement is such that others do not fit safely/properly.


If available it is certainly a lower impedance path, so in that sense superior as it might allow a MCB's "instantaneous" trip to clear a fault fast enough to avoid the main incomer time-delay RCD to trip.

However, others might argue that a TT earth rod in good condition has the advantage of being under your control and not having other voltages (e.g. lightning surge) superimposed on it.

PS the video was taken with my phone so although the video was taken right way up, it came on my computer as on it's side.

The photos are Front View, Top View and Underside View.

Regards

 

[pc1966]

What is the cable coming out bottom-left of the photo "Cutout Earth Block Bottom Underside View.jpg" as it looks as if the outer sheath is begining to perish?

 

[davesparks]

That's not the cutout/earth cover I was expecting it to be, I was thinking of one with a much smaller rounded cover.

I strongly suspect that it is TNS, but enquiry and testing is the only way to be sure.

I would be taking advantage of the TNS earth if it is available personally.

 

[pc1966]

I would be taking advantage of the TNS earth if it is available personally.

Would you keep the existing earth rod in circuit?

 

[davesparks]

Would you keep the existing earth rod in circuit?

Possibly, depending on its condition, resistance to earth etc.

 

[MartinJ]

What is the cable coming out bottom-left of the photo "Cutout Earth Block Bottom Underside View.jpg" as it looks as if the outer sheath is begining to perish?

Good Afternoon, It is the cable supplying the Cooker circuit.

They are all PVC cables what you see on the cables is dust.
I just didn't think about cleaning them before taking the photos/video.
The same goes for the tails coming from the bottom of the cutout in the video.
I assure you though, dust is all it is.

Regards
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[pc1966]

They are all PVC cables what you see on the cables is dust.
I just didn't think about cleaning them before taking the photos/video.
The same goes for the tails coming from the bottom of the cutout in the video.
I assure you though, dust is all it is.

Probably is just dust or spider's web, it was this bit that worried me:

Again, probably with a quick clean using an old pain brush or similar it would look fine.

 

[MartinJ]

If it has been fed with a split concentric cable then it will be TNS.

Overhead TNS distribution is rare but it does exist, so it is possible that this is what you have.

I know the type of cutout you are describing, that plastic cover does come off t reveal the earth terminal, but you do need to get it confirmed that it as a suitable earth before connecting to it.

Your best/safest bet is to contact the DNO to get them to confirm what type of eartjing system is provided. You may have to get them to visit to give a satisfactory answer as they might just say TT over the phone to get away without doing anything.
But remeber you probably won't get anywhere with a non-emergency callout at the moment.

Good Evening
Although You you and pc1966 have been very helpful, which I am extremely grateful for, I have attached some drawn diagrams of how things have been over time.
(BTW, the current CU was installed more around 1996).
You can see the layout pre 1990, 1990-1996 (with no effective Earthing!!!) and the current layout.
My idea of what happened (however I cannot be totally sure) is when the house was initially rewired in the early 80s with the 3036 CU, is my father (although he didn't re-wire the actual house himself) installed a small (obviously ineffective, in dry rocky ground) *Earth rod outside, but unaware of an Earth *already provided from the overhead supply.
When the new cable and cutout was installed in 1990, and he mentioned to the DNO chap he had previously installed an Earth rod, he claimed the DNO chap suggested there was an Earth on the poles supplying the house, and with regard to been told this, probably *assumed the Earth was connected and in place (however, the Earth cable from the 3036 CU was left dangling, since if it was meant to be connected to the DNO Earth, it was too short to reach the new cutout (and of course the 'pinch' mark left in the bared end I tend to remember).
*my father, just like many others, is not very familiar with electrical circuitry, so I do not consider this as his fault in any way.
The Earth rod and cable in use is still the same, but the cable was relocated lower down when the new CU was installed.
Please see the diagrams for more information.
PS I have used the colours Red, Black and Green to denote Line, Neutral and Earth cables respectively.

Kind regards.
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Probably is just dust or spider's web, it was this bit that worried me:
View attachment 58106
Again, probably with a quick clean using an old pain brush or similar it would look fine.

HI,
Yes, there is a load of dust and spiders webs around there.

You and davesparks have been very helpful.

I have just replied to one of davesparks' posts with some drawn diagrams of how I tend to remember things over time, with a few explanations on them (although generally what I have said earlier). Please refer to the diagrams.

Kind Regards.

 

[pc1966]

wire the actual house himself) installed a small (obviously ineffective, in dry rocky ground) *Earth rod outside, but unaware of an Earth *already provided from the overhead supply.

Has a more effective local earth rod now been installed?

Unless you are getting a rod impedance reliably below 200 ohms (less is better, obviously) then you ought to peruse the DNO about the suitability of their earth and arrange for them to connect to it.

 

[MartinJ]

Has a more effective local earth rod now been installed?

Unless you are getting a rod impedance reliably below 200 ohms (less is better, obviously) then you ought to peruse the DNO about the suitability of their earth and arrange for them to connect to it.

It is still the same Earth rod in place, although showing no signs of corrosion etc.
Perhaps I should not have stated 'obviously ineffective', however, although one cannot be sure without a Professional Loop Impedance instrument to measure the Ze and therefore give a specific numerical Ze value, the ground the rod is situated in is fairly dry, rocky and is nowhere near within the 'General Mass' of earth, in line with the transformer (which supplies the OH line) Earth rod.
If you walk from the back of the house up to the transformer supplying the OH LV supply, it is a steep-ish uphill route, and the land consists of many rocks within the ground etc, so a very rocky place.

The lower down village, supplied from a totally different Network, is all PME, overhead supply. There is a pole in the road, near the bottom of the very long driveway to the house, with an Earth electrode running down from it (probably part of the PME 'Multiple' Earthing), but again this is on a much lower down level than the mass of earth the house rod is situated in. Again, the driveway, land etc in between are very rocky and dry places.
On a side note, the Loop Value on a Kewtech 107 Socket Tester lit up as 'URGENT CHECK', i.e. over 93 Ohms as indicated in the Manufacturers Instructions (although I am aware personal opinions vary on such instruments).

If the chance should occur, I will definitely enquire regarding the DNO Earth.
In 2009, a visit from the DNO was made to the property to notify my parents that the cable running to the chimney pot (from the pole) is required to be removed and lowered from the chimney pot.
Then either last year/year before another visit was made from them (yes it was 9/10 years since previously hearing from them) they visited again.
If there is another visit, I will try and enquire then.
Saying that, many bare OH lines in the area have been converted to the new twisted insulated (possibly sheathed as well?) conductors, so although a bit off-topic, if they end up changing the entire OH supply to the property, they won't use TN-S Earthing with a new line will they?, it will possibly be a case of a split-con cable connected to a TN-C-S Network.

Regards

 

[Cookie]

You have no idea how lucky you are to have a TN-S supply (at least the option appears to be there), one where the 11kv is also run on two insulated wires. I can't say for sure, but I'd imagine this supply would eventually go to TN-C-S when the secondary is upgraded as is typical today.

 

[pc1966]

of earth the house rod is situated in. Again, the driveway, land etc in between are very rocky and dry places.
On a side note, the Loop Value on a Kewtech 107 Socket Tester lit up as 'URGENT CHECK', i.e. over 93 Ohms as indicated in the Manufacturers Instructions (although I am aware personal opinions vary on such instruments).

The photos show plenty of vegetation around, so it is not as dry and rocky as some locations!

Still for a decent earth rod you probably need it to go down something like 2m or so. You can get 1m long SDS drill bits that would allow and easy-ish way to get down 1m depth and then see if you can drive a rod down further. Of course, you should always be aware of the possibility of hitting a pipe or buried cable (cable less likely I guess) and what some folks advise is to dig down 1m or so manually (e.g. fence post digging tool) as by that depth you ought to have found any utility pipes, etc.

Another option to get a better Earth is to make a deep but farily narrow hole (as deep as you can, basically) for the rod to be driven in then fill it with conductive concrete. That fills out in to the gaps and tends to retain moisture a bit better keeping the path to "true Earth" a bit better. You might find this cheaper elsewhere, but this is the idea:

Fursecem® Conductive Aggregate

Furse CEM conductive aggregate is designed to be added in place of sand and aggregate to cement to provide a conductive aggregate which lowers the resistance to earth

www.jointingtech.co.uk

Opinions on socket testers in these parts do vary, but the Kewtech Loopcheck 107 is actually a fairly good one. By "vary" I mean folk think they are pants, which is true if you compare it to a MFT operated by someone knowledgable, but as an affordable test for a DIY / home owner it s a damn sight better than nothing. The cheaper testers (£10 region) suffer from not detecting a high-Z earth, only one that is totally disconnected (above tens of kOhm in most cases).

So they won't detect some types of serious fault. Basically they prove bad, not good. If one tells you there is a problem then you need to do something about it, however if it says all is fine you could be fooled as it has not picked up on something like a high-R earth.

Also none of them pick out a N-E swap. If the socket is RCD protected that is quickly detected in use, but a lot of homes still lack RCD protection so not being able to show that fault is another grey area. Now usually the R1+R2 test with L-E shorted at the CU would reveal reversed polarity, but DIY socket change would not (and should not) be doing that, or a wander lead to check R2 would show it if mains was off (so N-E open at the house isolation switch), but again that is not a DIY/home owner sort of procedure.

 

[MartinJ]

You have no idea how lucky you are to have a TN-S supply (at least the option appears to be there), one where the 11kv is also run on two insulated wires. I can't say for sure, but I'd imagine this supply would eventually go to TN-C-S when the secondary is upgraded as is typical today.

HI
The thought of been lucky to have the TN-S (although not currently used) has crossed my mind a few times.
The OH Line I was told was installed in the early 1960s, the first time my parents cottage (and the other properties supplied from the same Transformer) had electricity installed.
The houses in the village just below (mentioned in a previous post) did not have electricity until the 1950s (when a row of 10 council houses were built) and the houses were supplied overhead with two cables (L&N) and employed a TT system, I think via the mains water pipe!!! (I am aware it was once permitted) although since the last 25+ years all cables supplying the village houses have been replace with ordinary concentric cable and PME'd.
So yes, I fully understand where you are coming from.
I have therefore often considered, for an Earth to be provided to my parents cottage (and the two other properties) initially at the time (early 1960s) of the OH Line being installed was, in the very remote country concerned, a PRIVILEGE.
To put this another way, it is a shame for a solely separate Earth cable on the pole to be there, serving no purpose whatsoever, when possibly available for use (although it only serves a purpose for Earth Leakage faults, which are probably a very rare occurrence in practice, but I consider that being beside the point).

Kind Regards

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HI
The thought of been lucky to have the TN-S (although not currently used) has crossed my mind a few times.
The OH Line I was told was installed in the early 1960s, the first time my parents cottage (and the other properties supplied from the same Transformer) had electricity installed.
The houses in the village just below (mentioned in a previous post) did not have electricity until the 1950s (when a row of 10 council houses were built) and the houses were supplied overhead with two cables (L&N) and employed a TT system, I think via the mains water pipe!!! (I am aware it was once permitted) although since the last 25+ years all cables supplying the village houses have been replace with ordinary concentric cable and PME'd.
So yes, I fully understand where you are coming from.
I have therefore often considered, for an Earth to be provided to my parents cottage (and the two other properties) initially at the time (early 1960s) of the OH Line being installed was, in the very remote country concerned, a PRIVILEGE.
To put this another way, it is a shame for a solely separate Earth cable on the pole to be there, serving no purpose whatsoever, when possibly available for use (although it only serves a purpose for Earth Leakage faults, which are probably a very rare occurrence in practice, but I consider that being beside the point).

Kind Regards

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Also, if the OH Earth had been suitable for use all along, then that possibly means the necessity to fork out on the cost of the TD RCD in the CU currently installed was not justified!
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The photos show plenty of vegetation around, so it is not as dry and rocky as some locations!

HI
I understand what you are saying, but the Earth rod is directly outside the house in the garden right by the porch wall, in a fairly sheltered location.

NB I am not implying that you have misunderstood the photos, I just wasn't sure of your post above, but to clarify, the photos shown are the area between the Transformer and the cottage i.e. all photos shown are behind the cottage, I haven't posted any photos from between the front of the cottage and the road.

Regards

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The photos show plenty of vegetation around, so it is not as dry and rocky as some locations!

HI
I understand what you are saying, but the Earth rod is directly outside the house in the garden right by the porch wall, in a fairly sheltered location.

NB I am not implying that you have misunderstood the photos, I just wasn't sure of your post above, but to clarify, the photos shown are the area between the Transformer and the cottage i.e. all photos shown are behind the cottage, I haven't posted any photos from between the front of the cottage and the road.

Regards

Sorry, something has gone wrong with the quoting

HI
The thought of been lucky to have the TN-S (although not currently used) has crossed my mind a few times.
The OH Line I was told was installed in the early 1960s, the first time my parents cottage (and the other properties supplied from the same Transformer) had electricity installed.
The houses in the village just below (mentioned in a previous post) did not have electricity until the 1950s (when a row of 10 council houses were built) and the houses were supplied overhead with two cables (L&N) and employed a TT system, I think via the mains water pipe!!! (I am aware it was once permitted) although since the last 25+ years all cables supplying the village houses have been replace with ordinary concentric cable and PME'd.
So yes, I fully understand where you are coming from.
I have therefore often considered, for an Earth to be provided to my parents cottage (and the two other properties) initially at the time (early 1960s) of the OH Line being installed was, in the very remote country concerned, a PRIVILEGE.
To put this another way, it is a shame for a solely separate Earth cable on the pole to be there, serving no purpose whatsoever, when possibly available for use (although it only serves a purpose for Earth Leakage faults, which are probably a very rare occurrence in practice, but I consider that being beside the point).

Kind Regards

HI
The thought of been lucky to have the TN-S (although not currently used) has crossed my mind a few times.
The OH Line I was told was installed in the early 1960s, the first time my parents cottage (and the other properties supplied from the same Transformer) had electricity installed.
The houses in the village just below (mentioned in a previous post) did not have electricity until the 1950s (when a row of 10 council houses were built) and the houses were supplied overhead with two cables (L&N) and employed a TT system, I think via the mains water pipe!!! (I am aware it was once permitted) although since the last 25+ years all cables supplying the village houses have been replace with ordinary concentric cable and PME'd.
So yes, I fully understand where you are coming from.
I have therefore often considered, for an Earth to be provided to my parents cottage (and the two other properties) initially at the time (early 1960s) of the OH Line being installed was, in the very remote country concerned, a PRIVILEGE.
To put this another way, it is a shame for a solely separate Earth cable on the pole to be there, serving no purpose whatsoever, when possibly available for use (although it only serves a purpose for Earth Leakage faults, which are probably a very rare occurrence in practice, but I consider that being beside the point).

Kind Regards

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[automerge]1589849542[/automerge]

Also, if the OH Earth had been suitable for use all along, then that possibly means the necessity to fork out on the cost of the TD RCD in the CU currently installed was not justified!
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Also, if the OH Earth had been suitable for use all along, then that possibly means the necessity to fork out on the cost of the TD RCD in the CU currently installed was not justified!
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I don't know what's happening, but the quoting is going all wrong for some reason.

Regards

 

[Cookie]

HI
The thought of been lucky to have the TN-S (although not currently used) has crossed my mind a few times.
The OH Line I was told was installed in the early 1960s, the first time my parents cottage (and the other properties supplied from the same Transformer) had electricity installed.
The houses in the village just below (mentioned in a previous post) did not have electricity until the 1950s (when a row of 10 council houses were built) and the houses were supplied overhead with two cables (L&N) and employed a TT system, I think via the mains water pipe!!! (I am aware it was once permitted) although since the last 25+ years all cables supplying the village houses have been replace with ordinary concentric cable and PME'd.
So yes, I fully understand where you are coming from.
I have therefore often considered, for an Earth to be provided to my parents cottage (and the two other properties) initially at the time (early 1960s) of the OH Line being installed was, in the very remote country concerned, a PRIVILEGE.

Massive privilege. TT and TN-C-S are simply comprises (trade offs between various disadvantages/risks) in a world where utilities refuse to provide more than the bare minimum number of conductors that will light a light bulb or spin a motor. If I had to choose between IT, TT, TN-C-S and TN-S, I would hands down choose TN-S.

Low Z fault path, no stray voltage or current, no shock danger from a broken neutral (PEN), no danger from a failed RCD during an indirect contact fault, reduced line noise in old audio equipment... I'm forgetting about a half dozen other advantages.

In the United States we have it way worse, in that not only does our MEN serve as an LV PEN, but also as a PEN for the MV system. Stray voltage is a big problem especially on dairy farms, swimming pools, caravans and the like.

http://www.ecs.csun.edu/~bruno/MultiGroundedNeutralFinal_4-17-7.pdf

To put this another way, it is a shame for a solely separate Earth cable on the pole to be there, serving no purpose whatsoever, when possibly available for use (although it only serves a purpose for Earth Leakage faults, which are probably a very rare occurrence in practice, but I consider that being beside the point).

That extra wire is a blessing that I wish everyone on earth could experience.

Also, if the OH Earth had been suitable for use all along, then that possibly means the necessity to fork out on the cost of the TD RCD in the CU currently installed was not justified!

If the PE coming in was good, then no, I don't think the RCD was needed back then.

I don't know what's happening, but the quoting is going all wrong for some reason.

Regards

Its ok, this has happened to me on other sites before

 

[pc1966]

If I had to choose between IT, TT, TN-C-S and TN-S, I would hands down choose TN-S.

Low Z fault path, no stray voltage or current, no shock danger from a broken neutral (PEN), no danger from a failed RCD during an indirect contact fault, reduced line noise in old audio equipment... I'm forgetting about a half dozen other advantages.

Yes, certainly my view on the matter as well!

The TN-C-S option would not be so bad if it were a ring circuit (so no single PEN break causing 'earth' to rise up) but I don't think that is ever done (ring on HV yes).

In the United States we have it way worse, in that not only does our MEN serve as an LV PEN, but also as a PEN for the MV system. Stray voltage is a big problem especially on dairy farms, swimming pools, caravans and the like.

It is not my area of expertise, but I think historically the UK has shared MV and LV earths at some transformers, but only if the substation Ra was below 1 ohm. However, I don't think that is allowed any more on new setups?