Is TNCS worse than TT earthing?

[ADS]

So basically, the decision to add a 'rod' to a TN-C-S system is the same as making the decision to run a PME supplied earth to an outbuilding - it is up to the designer/installer to make the decision, based on his/her knowledge of the characteristics of the installation - there is no definite 'yes you can' or 'no you can't'.

I'm happy with that.

 

[davetheglitz]

So the basic answer to OP is yes, you are allowed to rod a TNCS,

This wasn't actually the question - My question was is TNCS a better earthing system than TT.

This is why I always say it is a no no, as I said, asking a question such as can I just add a rod brings up 2 things,Does the poster understand the implications enough to be doing this,

And do the circumstances permit this?

Hang on Steps - I can answer that myself!!! No he damn well doesn't understand the limitations!! Diagrams are great at simplifying the thought process - but can miss out the basics!! From the original diagram - if the neutral is lost then the current going through the live and the neutral paths in the RCD is the same - rod or no rod. In effect the rod has done nothing much other than possibly lowering the touch voltage by a few millivolts (think of a cooker as the load - 7 or 8 ohms verses 200 ohms for a rod. I think several posters have said that but I've been too thick to realise!

Came up with another stupid idea - see attached which relied on the earth rod impedance being > 950 ohms and less than 1600 to allow the loss of neutral to be detected - but of course no good as soon as bonding goes in place.

Overall then - TNCS is c**p because of the lost neutral. Makes bonding ultra important.

TT is c**p because of the possibility of a N-E fault.

Perhaps my question should be which is worst!

Thanks everyone for your patience!