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