Earth Rod on TN-CS

[markthespark]

Hi ive been working at a place where a guy has been out to test the installation and found some problems i was sent to rectfy these.

On one part fo the installation, he mentioned that the main earth was a TN-CS system but didnt comply because there was an earth rod also installed.

Whats wrong with having an earth rod installed on a TN-CS system is it something to do with different potenials?

Ive asked a couple of people and knowone knows the correct answer.

Any ideas chaps?

Cheers

 

[TonyM58]

Mark

read the defintion of a TN-C-S system in Part 2 Defeneitions in BS7671:2001, in particular the diagram for a TN-C-S

the write up underneath specifically says that an earth rod may be required at the consumers installation (or words close to that, aint got the regs in front of me)

 

[markthespark]

Cheers mate ill have a look tommorow.

 

[alan]

TN-C-S is called a PME or protective multiple earthing .
Regular joints are earthed out via rods in the ground. In case the combined neutral earth open-circuit. This happens more often than you would think.
So any reading Ze higher than 0.35 has to be reported, because the Zs is compromised.