Unidentified domestic earthing

[Pinto Baz]

I have just been to a domestic property were the main supply cable comes in through the wall together with a seperate 16mm G/Y earth conductor. The main supply cable is typical modern black PVC cable and terminates into a Henley sevice head (cut out) whilst the G/Y terminates into its own black terminal block (the square black heavy duty type, often used to split into meter tails) It all looks no more than about ten years old, the property is well over 100 years.

Suprise, suprise... the other side of the wall is a solid slab of concrete. I have measure the loop impedance Ze, it is 0.8 and there is no RCD/ELD so I guess that pretty well rules out a buried earth spike. I suspect the distributer supplied the building as a TN-S and may well have extended a paper lead cable with a joint below the ground outside. I have seen such a trick done in a cellar but has anyone seen it done like this. The distrbution people (Central Networks) have no records for this property.

 

[Guest123]

With a Ze that low it would definately suggest a TN-S arrangement. The DNO can be a law to themselves when they want to be so yes they probably did joint the sheath or 3rd wire underground somewhere.

 

[nickblake]

I agree with lenny sounds like a TNS the 0.8 on the Ze is the maxium reading for that type of earthing arrangement

 

[Pinto Baz]

Thanks guys, I'm going to put TN-S. Though I am slightly tempted to invite the DNO back to fit a PME which they said they would do for £150, bet they would change that figure when they see the Concrete