TNS or TNCS ?

[PKBristol]

As per the title, what type of earthing system is this ?
From the sheath of the main incoming cable, underneath the main cut out, is a cable going to the MET block, looks original/very old, from this MET block come various earths going off to consumer units and switch fuses etc, so, TNS. However also coming from this MET block is another cable going to (or is it coming from) the neutral of the main cut out, so that's TNCS. This "TNCS" cable also looks old, same as the "TNS" cable.
Has anyone seen this before ?

Thanks, Paul.

 

[Liam12]

Never seen a cut out have the link between the neutral and earth outside it, Ze ?

 

[PKBristol]

Haven't done a Ze yet, this is in a shop, working shop, so don't want to be disconnecting their earth while they're open. I'm rewiring the flats above, 1st and 2nd floor.At the moment i've only been in the "electrical cupboard" at the back of the shop for a few minutes while i isolated the supplies to the flats above, 2 x switchfuses. (Yes i removed the fuses, not just switched it off).

Paul.

 

[Marnik]

Try measuring both PEFC and PSCC, if the results are the same then defo TN-C-S if not then TN-S

 

[PKBristol]

Whichever one it is, should both still be connected ?, that's more my dilema. Who am i to "make it" TNS or TNCS ? I think this is one for the DNO, i'm thinking i should be ringing them.

Paul.

 

[Marnik]

Good call and good luck

 

[PKBristol]

PEFC and PSCC 1.46kA. Ze 0.14.

 

[somersetsparks]

Fairly common mate, to find PME'd TNS supplies, You have a good earth, bonding in place etc. I trust. I would not worry at all mate, leave alone and tell DNO if you really want.
They won't do anything!

 

[GLENNSPARK]

i don`t get this....
so if both the neutral AND earth are star connected.....
then whats the issue with a PME connection where the old TNS has been left.....

 

[somersetsparks]

i don`t get this....
so if both the neutral AND earth are star connected.....
then whats the issue with a PME connection where the old TNS has been left.....

There is none, everything is fine!

 

[MarkieSparkie]

Whichever one it is, should both still be connected ?, that's more my dilema. Who am i to "make it" TNS or TNCS ? I think this is one for the DNO, i'm thinking i should be ringing them.

Paul.

Best of luck with that, lets know if you get any sense out of them so we can put the flags out and announce it to the world.

Old TN-S cables which have lost their earth continuity in the past are commonly converted to PME by local earth rods connected at convenient break points in the original 'TN-S' cable as this is cheaper for the DNOs than replacing the whole original cable. In modern times the head would be replaced with the familiar TN-C-S type, but years ago it was common to just create the external hybrid set-up you have.