Difference between TN-C-S and TNS?

[--tom]

How do i tell the difference between in-situ TN-C-S and TNS?

 

[Lectrician]

TN-S may have a visible seperate conductor entering the building for an earth, or the sheath of a lead cable may be used to supply the earth. You may also find that a SPLIT CONCENTRIC cable has been used to feed your property, and the earth connection is on the side of the service head. BUT this looks identical to a PME or TN-C-S system, and you cant tell with out removing the service head cover which it is. (you must not do that).

It is possible to do a loop impedance test from L to N and L to E to determine.

PME or TN-C-S have the earth connected to the neutral inside the service head, and you cant normally see this link.

 

[plugwash]

sometimes a PME is done by using a spare neutral terminal on the head rather than a specific earth terminal

 

[kai]

There ought to be a Label saying that there is a PME system in use, on the service fuse block or near it.

 

[plugwash]

sure but a missing label is no indication that the system is TN-S

 

[--tom]

Thank you all for your very informative replies.