Discuss TN-C-S or TT? in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

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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.
 
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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!!!!!!
 
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.
 
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.
 
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.
 
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).
 
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...
 
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...


Funny thing was I was also told that Only crimped distributions systems would be converted to PME. From EEB (as you know), was quite a few years ago though!!
Also every 3rd or 4th pole as you said in a previous post to be staked. If they are working on an area and having to fit all these stakes at the poles, It would make sence to sort the joints out at the same time. Saying that I have seen many soldered overhead PME systems, so maybe they have changed their rules or its been converted DIY.

Edit,, I think it was the old U bolt type joints they were more on about
 
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Funny thing was I was also told that Only crimped distributions systems would be converted to PME. From EEB (as you know), was quite a few years ago though!!
Also every 3rd or 4th pole as you said in a previous post to be staked. If they are working on an area and having to fit all these stakes at the poles, It would make sence to sort the joints out at the same time. Saying that I have seen many soldered overhead PME systems, so maybe they have changed their rules or its been converted DIY.

Edit,, I think it was the old U bolt type joints they were more on about

Can't say i've seen a soldered joint on an overhead system. All the joint's connections i've seen on such installations have been via multiple clamp connectors. On some of the very old overheads it was by means of splicing (a lost art form) and clamps.

Sorry if it wasn't too clear, but I was talking about underground cables (PILC and the like) that are being converted from TN-S to TNC-S/PME Where every joint will most certainly be soldered connections unless it's been repaired/replaced in recent years. Now converting every joint at the same time in those circumstances, would be both time consuming, very costly and be an intolerable inconvenience for those customers connected to that distribution line...
 
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...



Thank you !!! :):):):)
 
My typo above,, I did try edit it... One too many beers I think! Yep Beer and the Electricians forum makes for intresting reading :)
 
The dno will usually replace the main distribution cable under a street and rejoin all the other cables to properties etc. to it and leave them as TNS, You can usually tell this has been done as the Ze readings will be very low!
If you then have the cut-out replaced, they will have no problems connecting it as a PME supply, In fact if you ring in our area, they will tell you whether you are allowed to connect it PME, especially if the earth clamp is missing from a TNS cable.
In our area, there is virtually no 'true' underground TNS systems left
 
The dno will usually replace the main distribution cable under a street and rejoin all the other cables to properties etc. to it and leave them as TNS, You can usually tell this has been done as the Ze readings will be very low!
If you then have the cut-out replaced, they will have no problems connecting it as a PME supply, In fact if you ring in our area, they will tell you whether you are allowed to connect it PME, especially if the earth clamp is missing from a TNS cable.
In our area, there is virtually no 'true' underground TNS systems left

Your living in cloud cuckoo land if you think the DNO is going to replace a serviceable cable that still has many years of life in it, in TNC-S form. Apart from that, do you have any idea how much it would cost, to say dig-up/trench just a half kilometre of residential road lay a new cable and then joint for every house/dwelling, ...let alone how long it will take and the inconvenience to it's customers from having daily power outages while the work continues?? I can assure you, they wouldn't even think about such work, unless it was absolutely 200% necessary.... and even then they will be looking for other ways to get past the problem... lol!!!

Many under ground cables are in the process of being PME'd, which means that the distribution cable in question will in all likelihood be supplying both TN-S and TNC-S. Which is another reason why DIY N-E connections at a service head can be extremely dangerous. Only the DNO will know what section(s) of that distribution cable has been converted to TNC-S.
 
Your living in cloud cuckoo land if you think the DNO is going to replace a serviceable cable that still has many years of life in it, in TNC-S form. Apart from that, do you have any idea how much it would cost, to say dig-up/trench just a half kilometre of residential road lay a new cable and then joint for every house/dwelling, ...let alone how long it will take and the inconvenience to it's customers from having daily power outages while the work continues?? I can assure you, they wouldn't even think about such work, unless it was absolutely 200% necessary.... and even then they will be looking for other ways to get past the problem... lol!!!

Many under ground cables are in the process of being PME'd, which means that the distribution cable in question will in all likelihood be supplying both TN-S and TNC-S. Which is another reason why DIY N-E connections at a service head can be extremely dangerous. Only the DNO will know what section(s) of that distribution cable has been converted to TNC-S.

No I'm not living in cloud cuckoo land, and no I'm not sure of the cost but.... I do work for a DNO, I'm not gonna say which one, and I can tell you in our area, a lot of the main distribution cables have been replaced and yes it was a hell of a lot of work, on the other hand you are correct, the other remaining TNS cables have all been PME'd, so in our area PME is 99.9% available.
Please stop being so patronising.
 
Patronising i'm not!! You must work for the only DNO in the country that strips out complete local network distribution cables and replaces with new, along with all the branch lines joints off to the householders service cut-out. And if they Do, ....not to the point, where 99.9% of the area's LV network distribution cables have been replaced, or have been fully PME'd....
 
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.

To EN54 and Guitarists posts I also considered doing this on my overhead tncs/pme but would like your comments on the potential danger that may arise under broken neutral scenario, as i understand it as rare as it is, all metal will rise to 230v, now if i have the 'best' or lowest path of resistance to a secondary earth rod in my block of dwellings isn't all or the majority of the fault going to head my way ?

J
 

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