Visual check to determine tnc-s or tns

[Robo]

Is it always possible to determine between tnc-s and tns by visual inspection. Tnc s is obviously combined N and E in the dno cut out and earth come from inside cutout.

If it was a tns would the earth always be clamped to the lead sheath of the cable. Thanks

 

[Engineer54]

Exactly as you describe, so therefore Aways possible to determine between the two systems....

 

[Robo]

Today i saw a dno and i could just see through the base where cable entered. I could see un sheathed swa which went inside cutout. Is ther any chance this could have been a tns. seperate core for each L and N and swa for earth??

Or is a tns earth always clamped to outside of cable armour before in enters cutout??

Or would this have been a split con Tnc - s .

 

[Engineer54]

Always ''Outside'' the cut out!! Never seen a DNO cut out with a separate earth facility within the cut out enclosure.

 

[Robo]

Thanks mate

 

[brucelee]

yesterday i saw a 16mm earthing conductor to a bs951 clamped to supply sheath then a un-insulated swa to the terminalson the cutout for the connection terminal to make it TN-C-S
its a council house which has had a PIR done august last year so is this a TN-C-S or A TN-S lol or both I know the BS951 is a no no and the DNO need to sort ot as its there mess
no grommets where cables enter enclosure metal clad ccu 2 knockouts trunking with no lid shower IP4Xnot maintained , RCD tripping and wont hold in even with all loads and CBs off this is why i went round as its one of our friends and she was cooking tea was working then just tripped and that was that as it was Council and i wasnt getting paid told them to get council elecys out
they came tested and confirmed after 2 hrs it was the rcd they installed a double socket to one of the 2 ways working on the other side of the split load board which are both the up and down lighting circuits both 6A type Bs
these are all NICEIC contractors

I would go with ENGINEER as this is my opinion also he is spot on

 

[Sparky Ninja]

 

[aptsys]

As widdler's diagram shows, if the property is supplied with splitcon then it is not possible to visually check unless you remove the cover of the cut-out. My old house was supplied in split con and to the untrained looked just like a TNCS supply.

 

[aptsys]

TN-C-S or TNS?...

 

[Phil]

i also had a property with what seemed to be tncs and tns. it had the earth coming from the sheath as well as the cut out so its not always possible just by a visual as to which one it is.

 

[oldtimer]

Why not just do a PFC test if L-E and L-N are exactly the same then it will be TNC-S no

 

[Robo]

Thanks for the help guys.

 

[aptsys]

TN-C-S or TNS?...

Answer was TN-S:

 

[Robo]

TN-C-S or TNS?...

View attachment 5481

Looks like a tnc-s to me but (is the earth normally exposed tho?)could be a split concentric tns supply as widdlers diagram show. Do pscc and pefc at mainswitch. If they are th same its tnc-s

 

[Engineer54]

Never personally seen a cut out box like the one shown, ....we live and learn!!! I would still say however that in the majority of cases, you would be able to visually determine the earthing arrangement of the DNOs supply...

If you were ever unsure, then a Ze test would soon determine/confirm as one or the other...

 

[topquark]

Never personally seen a cut out box like the one shown, ....we live and learn!!! I would still say however that in the majority of cases, you would be able to visually determine the earthing arrangement of the DNOs supply...

If you were ever unsure, then a Ze test would soon determine/confirm as one or the other...

You still can visually, you just have to remove the cover (no testing required).

 

[Engineer54]

Very true, but there are some that would be very skeptical about breaking seals!! ...lol!!!

 

[topquark]

Very true, but there are some that would be very skeptical about breaking seals!! ...lol!!!

Who, me

 

[KEVINDOE]

D.N.O now calls them " navy seals " ....if you mess with them ,youl be shot !!

 

[brucelee]

I had a 100A DP isolator fitted by british gas (unitied utilities) at my brothers so i can replace the two existing boards and tails , new digi meter
when i looked at the supply It has 2 supply cables I asked the meter guy was i TNS or TN-C-S

he said it was a TN-C-S but when i tested PEFC I got 2.5kA and PSCC 3.9kA on one board and on the other i got a higher PSCC of 4kA they are both fed from henley blocks which are in turn fed from the same supply
so if its TN-C-S then why the higher reading is it as i suspect that its because it has two supply cables not sure which is doing what

 

[aptsys]

I had a 100A DP isolator fitted by british gas (unitied utilities) at my brothers so i can replace the two existing boards and tails , new digi meter
when i looked at the supply It has 2 supply cables I asked the meter guy was i TNS or TN-C-S

It probably had two supply cables because it was a looped supply, so one of the cables would be supplying the next property.

 

[brucelee]

Hi mate cheers but thought looped supplies only happened on old terraced houses this is a semi detached and there is a drive and garage between both properties and thats the side the supply is

if it was a looped supply it would be on the other side i think the side that has the party wall I will post a pic if i can

sorry its not a good pic was took a while ago of my old phone i have a newer clearer picture

 

[Engineer54]

Just depends on how the DNO has wired there supply, seen detached executive houses loop wired in the Kent area. In this day and age it saves them money on joints and labour costs ... same old story throughout the industry really i guess ....Cost Cutting Rules!!!

 

[brucelee]

thanks engineer one of the cables is slightly larger than the other

how could i determine if its a looped supply without interfering with there equipment as they say we cant unless the seals fall out which is highly unlikely as they have just fit the isolator and tails to there side
the only place they havnt fitted seals now is the load side of the new 100A wylex D.P. i tried to look as he was doing it but its in a cupboard under the stairs soi couldnt get a good view

cheers suppose i will just have to take there word for it

the Ze was 0.09ohm and the pefc 2.5kA and the PSCC is 3.9kA on 1 board and 4kA on the other so it wouldnt have been possible to determine from measurement of the pefc or pscc if it was a TN-c-s but as we have seen in above posts that it can look like a TN-c-s but in fact is a TN-S

I am going with what the meter guy said as without taking the cover off theres no way to know for sure if its a looped supply or otherwise