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Posted By Topic: Main Earth onto steelwork in old building

Kingswell
Dec 11 2017 13:54

The main earth on a building about 50 years old is bolted onto the steel work at roof level, which is bolted to steel RSJs going down into concrete pillars. Would this have complied when built? If so, do I need to test resistance to remote test peg to prove it?
   

AlecK
Dec 11 2017 15:16

Since 1976 (at least) the requirement has been for an independent , dedicated earth electrode. R 157 specified various either driven vertical or laid horizontal types, though also allowed for alternatives approved by the Electrical supply authority.

For older, I believe probably would not have complied; as the old way was to use a waterpipe that was in most cases electrically continuous with an entire water distribution system. That methodology was prohibited from 1 April 1969 unless an agreement was in place between ESA and Water Supply authority allowing it.

Methods of testing the effectiveness of earth electrodes are given in "3017"; however there is no requirement for effectiveness, only a requirement for not exceeding max impedance of the main earthing conductor.

   

Kingswell
Dec 11 2017 18:21

Thankyou, Alex. The waterpipe inside this building is mainly copper - but it is not bonded or earthed, and doesn't appear that it ever was!
   

pluto
Dec 11 2017 22:33

Prior to 1976 EWR rergulations using the big building foundations was a normal way to get a good earth electrode and is still a good way to get decent earth connection.
   

Kingswell
Dec 12 2017 07:38

Thanks Pluto. I'm sure this building was there before 1976, and as this area is basically solid rock, driving an electrode would be impossible. I don't understand why the copper waterpipe was never also utilised, but that's slightly irelevant now, as it's no longer "electrically continuous with an entire water distribution system". But I will bond it.
   

AlecK
Dec 12 2017 09:04

Connecting to reinforcing of concrete foundations is mentioned in Notes to R 157 of the '76 Regs as a way around the difficulty of using either of the normal electrode types where the building occupied the entire site. The key then, as now, is connection to the actual reinforcing and not just to something bolted onto the concrete - along with the absence of any DPC between the concrete and mass of earth (which is why many slab floors of houses are not suitable).

Connection to structural steel doesn't get a mention, but may well have been approved by SA under (1)(c) covering alternative types.

Worth remembering that up until 1993, officially ALL installation work was supposed to be inspected by the Supply Authority. In practice this didn't always happen for minor work. But we do have grounds to reasonably believe that any mains or main earthing systems were inspected and passed by the local SA inspector when new.