High earth reading

[Inderpal]

Hello all

I need some advice . So I have a high earth reading electrician came out and said my earth reading is 235 which is very dangerous . I have my electric meter underneath my staircase in a cupboard

He said the easiest way he can fix it is put in a tts cable from my garden through my kitchen in the where the meter is . He has quoted me £600.

I have spoken to UK power network and they have said they won't install a new pme? System or do anything as yes it their earth wires but it's a Tenby system and they can't work on it ?

Any advice I have attached pics

 

[333rocky333]

Its a TN~S system, Looks like 2 cables, its possible your neighbour has same problem

 

[ericmark]

NOTE 2:* The resistance of the installation earth electrode should be as low as practicable. A value exceeding 200 ohms may not be stable. Refer to Regulation 542.2.2.

So the reading is just over the limit, but I would not say

very dangerous

How much work is involved to sink an earth rod I don't know, but two earthing systems must be a reasonable distance apart, as @333rocky333 says, possible your neighbour has same problem, but also likely if one property is changed from TN to TT then it is likely down to the DNO to tell you what earthing system you must use, so that both you and neighbour have the same system.

It is not set in stone, but it will require a site visit and risk assessment to ensure any water or gas pipes between properties do not import or export an earth.

My own parents had a similar problem, I will guess in 1954 when the house was built, the water pipes formed the earth, but in 2004 there was no evidence of there ever being an earth. All I could find was the GPO earth for the party line telephone.

To measure an earth, there are two methods, one is to lay out cables and put prods into the ground and working out the ohms independent of the supply, very hard with an existing home, as often one simply can't put the prods into the ground, due to concrete, tarmac, fences etc. So the other method is to compare the homes earth with the DNO earth. This method is reliant on the supply. But is the normal method used.

So depending on the property it could be costly, but the DNO should be saying what you are to use, not the electrician, but you can put in an earth rod as well as the TN earth, I have this with my own house, this is because I have back up batteries, and should the DNO supply be lost, still want an independent earth, but this has to be an on site decision not something debated on a forum, sorry.

 

[JohnW2]

So the reading is just over the limit, ...

Just over the limit for TN-S ?

 

[FrodoOne]

I need some advice . So I have a high earth reading electrician came out and said my earth reading is 235 which is very dangerous

Presumably, the 235 is 235 Ohms - NOT 235 Volts !

I have spoken to UK power network and they have said they won't install a new pme? System or do anything as yes it their earth wires but it's a Tenby system and they can't work on it ?

PME - Protective Multiple Earthing. (https://connections.nationalgrid.co.uk/make-a-change/replace-equipment/earthing-pme-service/ )
Why is it "their earth wires" (TN-S system?)
and
what is a "Tenby" system ?

Its a TN~S system, Looks like 2 cables

Yes - TN-S
It looks like two cables, (Line and Neutral)
with the PE derived from the Sheath of one of them (Neutral) as noted in https://en.wikipedia.org/wiki/Earthing_system
"the armoring of the supply cable is commonly used as the PE conductor between the transformer and installation rather than a dedicated conductor within the supply cable."

As long as the PE derived from the Sheath is intact (back to Earth on the system - somewhere) there should be no problem, as far as overload protection is concerned.
Hence, a "local" earth connection would not be necessary !

However, Is this the PE "connection" that reads 235 Ohms ?

"The sheaths on some underground cables corrode and stop providing good earth connections, and so homes where high resistance "bad earths" are found may be converted to TN-C-S" (ibid)

If this is a TN-S supply
and the PE "supply" has gone "bad",
surely it would be the Supply Authority's responsibility to provide a PME
or
allow the conversion of the TN-S supply to TN-C-S ?

A TN-C-S would also have only Two "supply" cables
Line and Neutral,
with the Neutral connected to the (local) Earthing Electrode,
which then provides the PE - at the same potential as the Neutral, whatever that may be.

Has this been a TN- S system which has been converted to a TN-C-S system, necessitating a Local Grounding Electrode?

(There is a 4 or 5 connection "Earth" Block under the CU.
Is there any local Earthing Electrode Conductor now provided?
What is the purpose of the two conductors going down from this Earth Block - one fixed to the wall and one hanging loose?

If it has been TN- C converted to TN-C-S, there should still be no problem with "overload" protection,
since the PE will have been connected to the Neutral.


A TT system would also have only Two "supply" cables - with no PE provided

The disadvantage of this is also noted in https://en.wikipedia.org/wiki/Earthing_system
where it is stated :-
"A big disadvantage of TT systems is that the impedance of the earth path is often so high that it can prevent overcurrent protection devices from breaking the supply sufficiently quickly to meet safety regulation.
This issue though can be addressed by instead relying upon RCD protection, which does not require a large fault current to activate.
In the pre-RCD era the TT earthing system was unattractive for general use because of this difficulty of achieving reliable automatic disconnection of supply (ADS)."

 

[Murdochcat]

Were you in the house when that fuseboard was fitted? Did you get an EIC? If so what was the stated reading at that point?

Where did this new spark connect to the main earth?

 

[Inderpal]

It was my grand parents property I only moved in 6 months ago. So I unfortunately have no idea

 

[ebee]

The supplier of your electricity should inform you what tge earthing system is and if its declared as T N (TNS or TNC-S) then they are responsible for repair if faulty on the incoming.
Looks like it might have been TNS and somebody decided to connect a broken off Earthwire using a "Temby" earthclamp.

 

[Murdochcat]

It was my grand parents property I only moved in 6 months ago. So I unfortunately have no idea

I do recommend you get this re-tested and the spark should do the Ze “inside” the CU and again with the earth connection directly to the service head connection

As for the DNO saying they can’t touch the income - they are the only people that should be touching it unless this is a flat

 

[crystal ball]

Had a few of these type faults, DNO came out same day and either sorted or stuck a front end RCD in as a temp fix

 

[ericmark]

Just over the limit for TN-S ?

Yes, TN-S we are told 0.8Ω and TN-C-S 0.35Ω, but the criteria are, it needs to be low enough to operate the protective device. If that device is a 30 mA RCD, working on the idea under fault conditions any live wire over 50 volt needs to trip the device if connected to earth, then 50/0.030 = 1666Ω a little odd with an overload device we work one 230 volts, so 230/(32 x 5) = 1.44Ω add 5% for safety 1.38Ω the times 5 is for a B32 and the B means the magnetic part of the overload will work at between 3 and 5 times the thermal part, and the thermal part is too slow to comply with regulations.

The fault needs correcting, but to frighten the occupants unnecessary that their electrics are super dangerous is not helpful.

The supplier of your electricity should inform you what tge earthing system is and if its declared as T N (TNS or TNC-S) then they are responsible for repair if faulty on the incoming.
Looks like it might have been TNS and somebody decided to connect a broken off Earthwire using a "Temby" earthclamp.

This is what I feel, the DNO tell the user what the supply is, so all users where their earths could close to each other are using the same system. If the DNO says it is TN-S or TN-C-S then they must get the earth loop impedance to 0.8Ω or 0.35Ω with a 100 amp supply. If however the DNO tell you the supply is TT then you need an earth rod, if the DNO don't know, then they will need to visit the site, but they tell you, not the other way around, so all properties on that supply are kept the same.

Since there is RCD protection already, it only needs an earth rod to make it TT.

 

[Jurassicspark]

Pop in your neighbors house and see what the earthing arrangement is.

If it's TN-S then the DNO should be able to change it to a PME.

If it's TT then you'll need to ask the electrician to install an earth rod. I highly doubt it is.

 

[Inderpal]

The dno saying they won't touch it because of the tenby clip so it's no longer their responsibility

 

[JohnW2]

Yes, TN-S we are told 0.8Ω and TN-C-S 0.35Ω, but the criteria are, it needs to be low enough to operate the protective device. If that device is a 30 mA RCD, working on the idea under fault conditions any live wire over 50 volt needs to trip the device if connected to earth, then 50/0.030 = 1666Ω ....

Indeed - but it appears that (whether the DNO did it or not) the OP's installation is 'wired as' TN-S, in which case one cannot rely on an RCD to provide fault protection - and, if it is TN-S, then any Ze over 0.8Ω would clearly need attention.

a little odd with an overload device we work one 230 volts, so 230/(32 x 5) = 1.44Ω add 5% for safety 1.38Ω ...

I gather that "5%" exists for 'international reasons'. In the UK, it really should be 6%, so as to ensure adequate TNCS down to supply voltages of 230 V - 6% (216.2 V).

 

[JohnW2]

The dno saying they won't touch it because of the tenby clip so it's no longer their responsibility

It could be that the DNO are saying that because of that clip (which they wouldn't use), that earth' connection to the cable sheath must have been installed by someone other than themselves in what they regard as a TT installation - and if that were the case, they would have no responsibility for providing an earth, which you would have to provide with your own earth rod.

As has been said, it would be interesting to know what earthing arrangements your neighbours have - if yours is meant to be TT (until someone tried to turn it into TN-S), then the same (or subsequent conversion to TN-C-S/'PME') would probably be true of your neighbours.