Connecting an earth

[Andy B]

I`ve re-wired a house and was going to keep it as a TT system. The house is in the country and this is what they had before I re-wired. The electrician testing and signing of the installation said the main earth can be connected at the neutral in the head? Where would I connect this up? Or should I leave it as a TT?

 

[topcop999]

It sounds to me that the installation supply may have been upgraded from a TT (overhead cables) to a TN-C-S (PME) system. This is something you could clarify with the distributor.

If it has been upgraded to a TN-C-S system then the inspector is correct, you can connect in at the supply head. Basically the distributor should have created a main earth terminal which pokes out of the supply head, next to the neutral termination. This is where you connect your earthing conductor. I would suggest you would need a 16mm earthing conductor to supply your consumer unit. It may be 10mm at present. You can then do away with the earth electrode. You may get a more stable and reliable earth than a TT system, it will certainly be a lower value resistance path.

The image below shows an older type of PME supply with the earth connection. Some of the recent distributors heads have a seal on the access to the earth block and they will put a Main Earthing Terminal block nearby for consumer use.

***CAUTION*** If you have any outbuildings supplied, and they contain extraneous conductive parts, you would not continue the TN-C-S earth into those. You would still employ a TT based system for those separate outbuildings and give the outbuildings an earth rod, with RCD protection.

Earthing is a complex area and it is vital you use a qualified person to undertake and test the works.

 

[Andy B]

Thanks for your help.

It looks like a fairly new SWA coming into the house. I took the cover off the head and found the neutral link. There is terminals but not one that pokes out of the supply head. Should I connect up inside the head? Maybe I`ll let the tester connect the earth.
Thanks again.
Andy

 

[Andy B]

Ok I`ve just seen the picture and its not that type of head.
Thanks

 

[topcop999]

What you a re describing is a newer type of TN-C-S (PME) head of which I have no piccies, however the principle is the same... They just protect the connection under a little access flap. Your tester should be able to do an external earth fault loop impedance measurement at the head, to determine if the system is set up as a TN-C-S. If in doubt clarify with the local supplier... its usually just a quick phone-call... The fact that you have a new incoming cable sounds as if it has been upgraded.