I think D is a far more interesting conductor to tag a name on.

Any takers for a classification for conductor D  in that diagram?

I think D and A are the same conductor, namely the big CPC for the whole site - I'd not use any term with 'bond'' in the name. The fact it has a MET (Main or Marshalling Earth Terminal )part way along does not alter the primary function of  being the thing the ADS in the consumer unit depends on - cut either and you cannot be sure that fuses blow any more.
The plumbing bonds could have joined at the CU end or at the incomer end and not alter that.
Equally I'd not say someone was wrong if they referred to either A or D  as the "main earth" - just as long as they did no slip in the word 'bond', .  not a question with clear cut 'always right' answer so rather a nasty one.

Mike.

CPC

mapj1  Interesting, and I don't think I disagree - but are D and A the same in terms of BS 7671 definitions?

I'm not sure they are (unless you say you have two METs - but then which is actually the main one?

Stuart Urban said:

CPC

Well, that would seem logical if you go with the fact that D can't be the earthing conductor ... It is a cpc if you take the view that it connects exposed-conductive-parts of both equipment on final circuits, and the consumer unit (if metal) to the MET.

So, it's a circuit protective conductor without a circuit of its own - or a cpc for all circuits (as this is the link to the MET).

Interesting.

I'd say it's a CPC for the circuit from the Service Head, through the meter and terminating at the Consumer Unit. I'd say Fig 2.1 in the book agrees with me. To me, there could only be any ambiguity if the MET wasn't labelled.

I'd say it's a CPC for the circuit from the Service Head, through the meter and terminating at the Consumer Unit. I'd say Fig 2.1 in the book agrees with me. To me, there could only be any ambiguity if the MET wasn't labelled.