Identifying supply type

[Richard3009]

TNS and TN-C-S can appear the same at first observation, other than opening and looking in the cutout for the amount of incoming cores and the link , how else can you tell the difference.

 

[Simonslimline]

on a TNCS the pscc and pefc should be the same

 

[Richard3009]

Im talking about visually identifying a supply type using no instruments

 

[Simonslimline]

Most of the TN-S systems I have seen have had an earth sweated on to the cable sheath.

 

[Richard3009]

Split concentric being the exception it looks just like TN-C-S but isnt.

 

[Simonslimline]

Alot of the time there is a label saying its a PME system, my flat is PME and done using straight concentric cable. There is a label saying this system is a protective multiple earthing.

 

[Richard3009]

And without the label, how would you find out

 

[Simonslimline]

phone the DNO

 

[telectrix]

phone the DNO

but have a good supply of beer and smokes to hand.

 

[Richard Burns]

This post has some useful information and photos addressing the issue you raise.

 

[Richard3009]

What about the system that uses a concentric cable with 3 cores so its a TNS system but looks like a PME, the only way to tell is by opening the cutout to see if its a 2 core with linked N (TN-C-S) or 3 core (TNS)

 

[Richard Burns]

I do not think any DNO would use a three core concentric cable for a single phase, at the lengths of cable they are using cost is a primary factor.

 

[Richard3009]

File:TNSUsingPMECutout3.jpg - DIYWiki how about this

 

[Simonslimline]

What about the system that uses a concentric cable with 3 cores so its a TNS system but looks like a PME, the only way to tell is by opening the cutout to see if its a 2 core with linked N (TN-C-S) or 3 core (TNS)

So you mean a split concentric. Other than my other answers I am not sure really.

 

[Richard3009]

If the cover was on that cutout you would put money on it being a TN-C-S and you'd be wrong

 

[Simonslimline]

Yes but if you are not sure you can find out by enquiry. Also instead of guessing you can do your PFC tests to work it out.

Is this a genuine concern of you'rs ?

 

[Richard3009]

No just an observation I made on a supply yesterday

 

[Simonslimline]

Fair enough.

How did you identify it in the end ?

 

[Amp David]

Know what id do if i had no instruments to test with. Probably get shot down if i decided to post it though.

Why would you have instruments though in the first place?

 

[Richard3009]

split the cutout

 

[davesparks]

Why are so many people so keen to go taking the DNO's equipment to pieces just to be able to tick a box on a cert? And you will have your tester anyway if you are doing inspection and testing!

And if you are there to do a quote then in the average 100A SP supplied domestic environment there is no difference in what we have to install and how we have to install it between the TN systems, unless you are quoting for running power outside to an outbuilding containing extraneous parts (how many actually do).

There's even a suggestion somewhere that we should consider that existing TN-S systems may be changed to TNC-S in the future (more grey area nonsense from out IET masters)

 

[Rockingit]

Was thinking exactly the same as Dave - for average everyday domestic all we need to know is TN or TT and what the Ze is. Even a Electrical Trainee can suss that one, surely?!