TT vs TN-C-S - preference?

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My new property has an TT earth but at some point someone has put block paving over the earth spike location making it unservicable/uninspectable, although it is within acceptable impedance limits currently. The property also has a PME supply which is currently not connected to the installation earth.

So the options are to dig up the driveway to locate the earth spike and/or relocate it somewhere more suitable, or to ditch the spike and switch to a TN-C-S setup. Is there an order of preference when it comes to these things? The only additional factor is that we have an outbuilding wired from the main house fusebox including the CPC, which I beleive lends itself better to TT?
 
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My new property has an TT earth but at some point someone has put block paving over the earth spike location making it unservicable/uninspectable, although it is within acceptable impedance limits currently. The property also has a PME supply which is currently not connected to the installation earth.

So the options are to dig up the driveway to locate the earth spike and/or relocate it somewhere more suitable, or to ditch the spike and switch to a TN-C-S setup.

Or just add another earth spike and connect them together.
Is there an order of preference when it comes to these things? The only additional factor is that we have an outbuilding wired from the main house fusebox including the CPC, which I believe lends itself better to TT?
I hope you have a CU and RCD NOT a fusebox in this day and age. Please confirm.
 
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Forgive the casual terminology, it's a CU with RCDs yes.
 
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Due to electric cars and hot tubs, I would likely go for TT. But in theroy the DNO has the say on which you use ....
Where did that come from?

Although, as I understand it, the DNO are under no obligation to provide an earth, they may do so - but, if they do, it's down to the owner of the installation (not the DNO) to decide whether or not they want to use it.

I have been offered TN-C-S by my DNO, but I declined that offer and told them I am very happy to stay with my TT earth.

Kind Regards, John
 
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I believe there is a distance consideration so with a row of town houses then if one went TT and rest TN-C-S it may be possible to touch the two earth systems at the same time.

But where the two properties are far enough apart so you can't touch the two earth systems, there would be no problem.
 
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I believe there is a distance consideration so with a row of town houses then if one went TT and rest TN-C-S it may be possible to touch the two earth systems at the same time.
That's a theoretical possibility, but I still don't think the DNO can 'force' anyone to use their TN-C-S earth if they don't want to.

In any event, if the location of a fault were such that a 'lost PEN' (which is what everyone worries about) affected some, but not all, of your 'row of town houses', then a hazard similar to the one you postulate could arise even if they were all using a TN-C-S earth.

Kind Regards, John
 
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I believe there is a distance consideration so with a row of town houses then if one went TT and rest TN-C-S

My cottage and the adjacent retail unit were originally one property under the same thatched roof and the electricity supply to them was in the retail unit. Originally an overhead supply the installation was TT. When I bought the cottage I had to disconnect from the existing supply and have a new supply installed to the cottage. My new supply was TN-C-S for the convenience of not having to install a ground rod(s) in close proximity to the ground rod of the retail unit.

The complication of having TT and TN-C-S so close was the water service which comes to my cottage and also supplies the retail unit via a private meter. There has to be a non conductive section in the pipe feed to the retail unit to prevent the Neutral derived "Earth" in the cottage being connected to the ground rod derived Earth in the retail unit via the bonding connections and the water pipes .
 
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My cottage and the adjacent retail unit were originally one property under the same thatched roof and the electricity supply to them was in the retail unit. Originally an overhead supply the installation was TT. When I bought the cottage I had to disconnect from the existing supply and have a new supply installed to the cottage. My new supply was TN-C-S for the convenience of not having to install a ground rod(s) in close proximity to the ground rod of the retail unit.

The complication of having TT and TN-C-S so close was the water service which comes to my cottage and also supplies the retail unit via a private meter. There has to be a non conductive section in the pipe feed to the retail unit to prevent the Neutral derived "Earth" in the cottage being connected to the ground rod derived Earth in the retail unit via the bonding connections and the water pipes .
We were once called to a property complaining of electric shock from their outside tap, we found 2 houses with a narrow (~2ft ish) shared path between them and a brass tap on each house. The actual discovery of the PD between them was the children holding on to both taps at the same time and swinging on them.
 
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My father-in-law had a motor caravan, and regulations say a supply to it should be TT, but it was parked about 1.5 meters from the electric and gas meter cupboards, on concrete, slabs, so he used the TN-C-S supply, as a meter reader could touch both at the same time.

The supply was only to keep the battery charged, and put in really for the lawn mower, but with a semi-detached house, how does one know what joins the houses? I could make this house TT without a problem, there is at least 3 meters all the way around, but unless one is there when it is built, who knows what metal joins or nearly joins the properties? Or how close the earth rod is to underground metal services.
 
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My father-in-law had a motor caravan, and regulations say a supply to it should be TT, but it was parked about 1.5 meters from the electric and gas meter cupboards, on concrete, slabs, so he used the TN-C-S supply, as a meter reader could touch both at the same time.

The supply was only to keep the battery charged, and put in really for the lawn mower, but with a semi-detached house, how does one know what joins the houses? I could make this house TT without a problem, there is at least 3 meters all the way around, but unless one is there when it is built, who knows what metal joins or nearly joins the properties? Or how close the earth rod is to underground metal services.
Well I know exactly how close one earth rod is to the supply cable in a property, I was there when there was a bang and our site temporaries went off.
:( and it was only a few inches below the surface.
 
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Agreed but that would mean banning TN-C-S, can you really see that happening?
Of course not. I was merely pointing out was that a very similar concern to yours about having mixed TT and TN-C-S in 'a row of town houses' would still exist even if they are all TN-C-S.

The problem is TN-C-S, not having a mixture of it and TT.

Kind Regards, John
 
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Not a clue where my supply runs, I see a building which looks like a pill box in a field I assume transformer is in it. But could be a water pump for all I know. The power comes into the garage now a flat, but no idea of direction.

All my RCBO's are single pole switching, if using TT really need double pole switching, so unless I get a hot tub or electric car, it will remain as TN.
 
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The complication of having TT and TN-C-S so close was the water service which comes to my cottage and also supplies the retail unit via a private meter. There has to be a non conductive section in the pipe feed to the retail unit to prevent the Neutral derived "Earth" in the cottage being connected to the ground rod derived Earth in the retail unit via the bonding connections and the water pipes .
Unless I'm missing something, even if that happened, the situation would be no worse than if the retail unit also had a TN-C-S earth, would it? (and, for better or worse, TN-C-S is 'accepted').

As I've often reported, with main bonding connected, the "Ze" of my TT installation is around 0.25Ω, seemingly as a result of a metal water supply pipe and bonding connecting it to my neighbour's TN-C-S earth. As a result, every final circuit in the house has a Zs low enough for OPD-mediated ADS (although I obviously don't/can't "rely upon" that) - and I lose no sleep over the situation.

Am I missing something?

Kind Regards, John
 

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