TN-C-S or TT?

[Silly Sausage]

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.

 

[Engineer54]

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!!

 

[telectrix]

and i thought it was all to do with the painless removal of goolies.

 

[SPARTYKUS]

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.

 

[Engineer54]

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.

In what way??

 

[SPARTYKUS]

Good question. Just does. I didn't comment on said sample of electricians and their brain function.

Okay, I meant in the way that there are lots of things in the regulations and I am quite happy to admit I am rusty on things I do not spend time on (like Marinas).

But, having thought about it, should you now retort with something along the lines of "well basic knowledge of earthing systems should not throw any electrician", then I agree with you.

I only meant it can throw you for a moment or two. As a result of lack of familiarity.

 

[Jonny66]

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.


Paul

Thats what a Ze test shows (if done correctly) that you have an effective earth!!!!!!!!! tis the whole point!!!!!!

 

[Edd]

..........

 

[sjm]

Quite often the poles will have a large red PME sign on them, tends to be a bit of a giveaway really! lol

 

[Risteard]

Though one has to wonder what a Southern Irish TNC-S system is called, if it isn't as they put it ''Neutralised''?? lol!!

Sorry for the delay in getting back to this thread, but my understanding is that all TN-C-S "neutralised" supplies in the south of Ireland must have an earth rod fitted as well. Unfortunately I don't have a copy of the Electrotechnical Council of Ireland's (ETCI) ET 101 ("National Wiring Rules") to verify.

 

[Cbigfoot]

Depends where you took the ze from. If you took it with the earth connected to the neutral of the service head then you will get a low reading wherever you are and what ever supply you have as you are simply getting a reading through the phase and neutral conductors. This readin alone will not confirm a tncs supply.

Tncs supplies willnot have old cables on them. They require crmped connections, so the old cables with soldered connections would be removed. A pvc concentric service is usually a good sign that it has been upgraded.

I recently rewired a house that had a tncs service but had been left as a tt by the dno when the service was upgraded because there was no bonding.

 

[Edd]

..........

 

[Engineer54]

Sorry for the delay in getting back to this thread, but my understanding is that all TN-C-S "neutralised" supplies in the south of Ireland must have an earth rod fitted as well. Unfortunately I don't have a copy of the Electrotechnical Council of Ireland's (ETCI) ET 101 ("National Wiring Rules") to verify.

That's basically a very good standard to have, it's very much the same in most Western European countries too. Shame they don't insist on the same in the UK.

 

[Guitarist]

Well, I have just had my in-laws' cottage (overhead supply) changed from TT to TNC-S by UKPN and we now have a Ze of 0.33 ohms. I am going to leave the earth electrode connected also, which is a stable 70 ohms (measured 22 ohms with oil and water bonding connected).

 

[Engineer54]

Depends where you took the ze from. If you took it with the earth connected to the neutral of the service head then you will get a low reading wherever you are and what ever supply you have as you are simply getting a reading through the phase and neutral conductors. This readin alone will not confirm a tncs supply.

Tncs supplies willnot have old cables on them. They require crmped connections, so the old cables with soldered connections would be removed. A pvc concentric service is usually a good sign that it has been upgraded.

I recently rewired a house that had a tncs service but had been left as a tt by the dno when the service was upgraded because there was no bonding.

Well that's not completely true at all. So what do you think happens when a TN-S supply is converted to TNC-S/PME??
They will only use crimped connections when a joint is replaced, they certainly aren't going to replace every joint on the distribution supply run before converting a households service head. It maybe several years before a converted distribution cable is fully PME'd, and is more likely than not, supplying both TN-S and TNC-S during that period.

By the way, there is nothing wrong at all, with soldered joint connections, they have been around long, long before crimped connections, they are as sound as any crimp connection too. There are very few circumstances where soldered terminations are not advised or permitted...