earthing TN-s/tnc-s to TT

BristolSpark · Jun 13, 2012

Hi

I have a main earthing senario, cant veryfy the earth without getting into the house next, as the main earth comes from next door.

Its either a TNs or TNC-s. The question then lies as I am unable to find anything in the regs, can I install an earth rod to a garage supply and still utilise the existing earth supply in the property.

I thought I read somewhere that this was acceptable, due to possibilities of losing the earth via TNC-s due to neautral earth senario, but also recommended for TN-s as it will help with lower Zs readings.

Does anyone have experience of this and can someone verify if this is acceptable.

I am also debating on just running an additional TT from the house now, in 16mm just because I cant get into next door.

Any help and advice would be much appreciated..

telectrix · Jun 13, 2012

measure PSSC and PEFC if the readings are virtually identical, it's most likely TNC-S. what Ze reading did you get? as long as you have confirmed a TN earthing, then no need for a rod, but then again, no harm in banging one in.

tony mc · Jun 13, 2012

If you have a seperate earth which goes to next door it sounds like a TNS!

This earth cable should enter your property to the premises MET.

Have you done any testing to confirm a ZE reading?

The best way to confirm is to do some testing before going any further!

BristolSpark · Jun 13, 2012

There is 16mm incoming tails, they come through a metal conduit pipe in the wall. The earth cable looks to be a 4mm I will stretch to a 6mm but I believe it to be 4mm. This earth cable comes off the metal pipe and attaches to the MET. The other end of this pipe the cable then does in deed attach as a TN-s.

Next door has gone back out now,

As the board in this property needs upgrading at a later date. I was thinking of trying to get a 16mm earth through this pipe and make a direct contact at the TN-s location, then This board is setup to change the ccu at a later date.

In the mean time I need to feed a supply to the garage. Hence why I was considering a rod either at the garage, but still use main earth from property.

Have not done Ze at present, just visual.

Engineer54 · Jun 13, 2012

Nothing to stop you adding a Rod to a TN-S/TNC-S system, but we both know that a 4mm main earth conductor isn't exactly conducive to a good earthing conductor on a TN system. So either you manage to gain access to next door and get a 16mm through the conduit, or connect a 16mm conductor to each end of the conduit...

Do you have a DNO service cut-out in the property your working in?? If not, contact the DNO and ask for one. It's not acceptable for your service fuse to be located within another property and therefore not under your clients direct control. ...eg, What happens if the service fuse pop's while the neighbors are on there 2 week annual vacation, ...do the DNO break down the neighbors door to gain access to replace your clients service fuse?? lol!!