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phawk

Could anybody help me with this?

I'm starting a re-wire of an old property that has an overhead incoming supply. I've pulled the main fuse and there is a live & neutral supply, then the earth is taken from the neutral block (TN-C-S, right?). The problem I have is that I spoke to another electrician who seems to think that this shouldn't be the case if the supply is coming from overhead, as the system would need an earth rod, making it a TT system.

I've done a Ze which comes in at 0.20 ohms, and a PFC & PSCC which both come in at 1.17kA, which are well within the limits for a TN-C-S system.

So.......is the system earthed or not? Seems to me that it is but I want to make sure.

Also, the property has no gas (it has a stand-alone oil supply for the central heating). Where do I bond this?

Thanks a lot,

Paul
 
Could well be TNC-S, check with the DNO if it is supposed to be available in that area.

Test to confirm it needs to be bonded then bond back to the MET the same as any extraneous incoming service.
 
If it is an overhead supply and TT then there must be a tranny somewhere down the line, on a mast or something. But your test results point more to a TNC-S.
 
it sounds very much like TNC-S. why would the guy think it needed a rod at the property? he needs to study his earthing diagrams. bond oil pipe where it enters the building ( assuming it's metal pipe.)
 
Plenty of overhead supplies are TN-C-S mate, and pretty good ones too. Yours may well have been TT once upon a time, but for the last 20 years DNO's have been converting many on request.
Earth from neutral block and Ze of 0.2 ohms.... No-brainer really.
 
PME was first introduced in the UK to provide a reliable earthing system, for the then many rural overhead supplies. You can check for yourself, if the overhead system supplying this property has been PME'D or not. Walk down the poles a few hundred metres, if PME'd you will see that at every 3rd or 4th pole, a N-E grounding cable that's going down to an earth rod, will be clearly present.

Overhead PME systems are in essence the purest form of PME you will find. Also if you have an earth rod on the property leave it in place, and don't disconnect from the installations MET. Look at it as just another PME earthing point!!!
 
PME was first introduced in the UK to provide a reliable earthing system, for the then many rural overhead supplies. You can check for yourself, if the overhead system supplying this property has been PME'D or not. Walk down the poles a few hundred metres, if PME'd you will see that at every 3rd or 4th pole, a N-E grounding cable that's going down to an earth rod, will be clearly present.

Overhead PME systems are in essence the purest form of PME you will find. Also if you have an earth rod on the property leave it in place, and don't disconnect from the installations MET. Look at it as just another PME earthing point!!!

I go over to the West of Ireland once or twice a year, very rural!
I've noticed that a lot of the O/H supplies appear to be quite new, so I take it they'll be mostly TNCS?
Might take my meter over this time...I need to get out more!
 
I go over to the West of Ireland once or twice a year, very rural!
I've noticed that a lot of the O/H supplies appear to be quite new, so I take it they'll be mostly TNCS?
Might take my meter over this time...I need to get out more!

Supplies in the south of Ireland are almost all TN-C-S although they must be "neutralised".
 
Ive seen plenty terraced shared overhead supplies converted to tncs .... just had to get DNO out to allow me to connect to the newly provided earth on a board upgrade that had a earth rod existing from the tt days.
 
I did a quick google and found this...

From Wikipedia (I know, not a definite source!) for ESB, Irish supply company:

Earthing/Grounding System

  • TN-C-S is preferred. This is referred to in Ireland as a "Neutralised" supply. Most homes and businesses are connected to such a system.
    Where this system is used, all metal pipe work must be bonded i.e. connected to the system's earth/ground creating an equipotential zone.
In such an installation earth straps and yellow & green earth wires can be seen connected to pipework under sinks, in heating systems etc.

  • TT system is used where TN-C-S earthing is not possible due to the design of the local distribution network, or the geology. This system is referred to as 'unneutralised' or 'not neutralised'.
Where a TT network connection is used, the entire supply must be protected by an RCD
Converting a TT supply to a TN-C supply "Neutralisation" may only be carried out by an ESB engineer with the approval of ESB Networks. Under no circumstances should a home owner, or an electrical contractor make any connection between the Earth/Ground and Neutral. To do so inappropriately could expose people to a risk of serious shock or electrocution.


Is it just an Irish way of referring to TNCS/PME? They do have their own ways! :)
Hopefully our man will come back and clarify.
 
From Wikipedia (I know, not a definite source!) for ESB, Irish supply company:

Earthing/Grounding System


  • TN-C-S is preferred. This is referred to in Ireland as a "Neutralised" supply. Most homes and businesses are connected to such a system.
    Where this system is used, all metal pipe work must be bonded i.e. connected to the system's earth/ground creating an equipotential zone.

In such an installation earth straps and yellow & green earth wires can be seen connected to pipework under sinks, in heating systems etc.


  • TT system is used where TN-C-S earthing is not possible due to the design of the local distribution network, or the geology. This system is referred to as 'unneutralised' or 'not neutralised'.

Where a TT network connection is used, the entire supply must be protected by an RCD
Converting a TT supply to a TN-C supply "Neutralisation" may only be carried out by an ESB engineer with the approval of ESB Networks. Under no circumstances should a home owner, or an electrical contractor make any connection between the Earth/Ground and Neutral. To do so inappropriately could expose people to a risk of serious shock or electrocution.



Is it just an Irish way of referring to TNCS/PME? They do have their own ways! :)
Hopefully our man will come back and clarify.

Thanks for clearing that up ...lol!!!

Supplies in the south of Ireland are almost all TN-C-S although they must be "neutralised".

Though one has to wonder what a Southern Irish TNC-S system is called, if it isn't as they put it ''Neutralised''?? lol!!
 
Last edited by a moderator:
and i thought it was all to do with the painless removal of goolies.
 
If you're used to working in cities for years then work somewhere that has alot of overhead Tncs (like Stroud, for example which is very hilly) it can throw you, experienced spark or not.
 

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