TN-S or TN-C-S From this photo

[TonyJohnson]

Hi,
I undertsand this to be a TN-S system as the earthing arrangement comes along the SWA metal sheath surround but the Ze i got is 0.19 which falls out side the regs of 0.8.
Chameleon Electrical - https://www.facebook.com/Chameleonelectrical/photos/a.162578514404078/251251892203406/?type=3&theater

I have also read on here that if the earth is then connected to an earthing block as shown on picture, it then becomes a TN-C-S! which doesnt make sense as the earth is outside the sheath not inside on the neutral!

Which is it?

 

[SparkyChick]

That appears to be a loop through TNS supply.

The earthing block to which you refer is the main earth terminal for the installation. This can be a separate entity, as it is in your photo, or the earth terminal bar in the consumer unit.

The main earth clearly comes off the sheath of the cable (this is what makes it TNS) into the main earth terminal. If it was TNCS, the earth block would be on the other side (the neutral side) of the service head, usually with the main earth leaving the service head on the same side.

As for the Ze... 0.8 is the maximum recommended I believe (i.e. if it's more, give the DNO a call). 0.19 is much lower and so it's a fine example of a good earth. No problem there.

 

[Nigel]

Needs testing I woukd say to confirm.

 

[Midwest]

Thats a good Ze figure, is it not?

 

[chris gray]

Lol. I hate picking at pics but; stripping your tails back that far has left them single insulated. Just a pet hate

 

[MDJ]

0.19 is better than 0.80, so good there, however in answer to the question I would say it is TNS

 

[Wilko]

Should be TNS
Comparing Ze and L-N may help you decide.

 

[telectrix]

deffo TN-S,but why is the isolator fed in at bottom instead of at top?

 

[mhar]

Lol. I hate picking at pics but; stripping your tails back that far has left them single insulated. Just a pet hate

521.10.1 & 526.8

 

[bigspark17]

0.19 falls outside what value? Are you a trainee? These are worrying questions if you are an electrician!

 

[Ian1981]

deffo TN-S,but why is the isolator fed in at bottom instead of at top?

It’s an isolator so it makes little difference but looks annoying

 

[Loki]

If you are unsure if its a TNS or a TNCS system by looking at it ( ie not sure if its been upgraded to TNCS ) You could do a simple continuity test between the neutral & earth at the mains switch to confirm this.

 

[telectrix]

and it's not SWA. it's PILC (paper insulated lead covered).

 

[Toneyz]

Looking at the photo I have come to the conclusion it is TN-S as if it was an old TN-S and converted to TN-C-S there would have to be a link between the neutral block and earth all I can see is a link between the sheaths and a earth link between the sheath of one cable and a earth block.

 

[davesparks]

If you are unsure if its a TNS or a TNCS system by looking at it ( ie not sure if its been upgraded to TNCS ) You could do a simple continuity test between the neutral & earth at the mains switch to confirm this.

That won’t necessarily help as N and E are still linked at the substation for TNS so there is continuity between them in both systems.
Comparing the measured resistance may help, but it’s not guaranteed.