..but as I said is does not "list this as an E-C-P". It includes structural metalwork in a list of things that may be an extraneous-c-p (IF they satisfy the definition in Part 2) - but, just as central heating systems will not usually be extraneous-c-ps (even though they are in the list), nor does structural metalwork always have to be an extraneous-c-p because it's in that list.
"...to each building" [you forgot to complete the quote]. Sure, but that surely just means what it says. Things which are extraneous-c-ps (but not those which aren't) must be bonded whenever the 'enter' any building which is part of the installation - hence, if a water pipe enters both the house and an associated garage, both need appropriate bonding (possibly to different earthing systems).
My view is as above.
PBoD - I don't really understand question.
Whilst John is obviously and indisputably correct I will agree that that is not what 411.3.1.2 actually says.
Not, it doesn't say 'may', but I don't think it actually needs to, since English is not always the most unambiguous of languages. If I wrote "This requirement applies to metalclad accessories, including (i)sockets and plugs,(ii)...", I think that everyone would interpret that as meaning "sockets and plugs which are metalclad", and I hope that not many people would suggest that it meant that 'the list' was suggesting that all sockets and plugs are metalclad, and therefore acquired the requirement. Hence, I think that "extraneous-conductive parts including (say) central heating systems" is intended to mean "central heating systems which are extraneous-c-ps", not to suggest that all central heating systems are extraneous-c-ps. ... and the same for structural metalwork.
To be fair, I think the list includes all the common things which 'may' be extraneous-c-ps, plus some less common ones (like central heating systems).
...under as wide as possible a range of environmental conditions
...and the answer is equally simple ...
That would be earthing, not bonding - and the CPC (if there were one) in the cable that was cut should cause an RCD to operate in that situation. However, I agree that (e.g. if there were no CPC in the cable, and the cutting didn't cause an MCB to operate) then earthing the door would make it more likely that an RCD would operate, so that the cut end of the cable would no longer be live. However, that's a pretty improbable scenario you are describing. In nearly all other situations, 'unnecessarily' (because it didn't qualify as an extraneous conductive part) connecting garage metalwork to earth would increase the risk of electric shock - albeit shocks that occurred would hopefully (but not certainly) be non-fatal in the presence of an RCD.
As I've indicated, those are the situations which concern me, since it may not be possible to be sure that the metalwork would never become an extraneous-conductive part under certain environmental conditions. So, it's not simple - one might think that "if in doubt, then bond" would be 'safe' but, as I've just said, if that results in one 'unnecessarily' bonding, then the result will be an increase in the risk of electric shock (and any electric shock may prove fatal, even with an RCD). It therefore requires a careful 'balance of risks' assessment.
We know that views vary but, in general, I'm inclined to agree with that approach. However, one has to realise that if one does that, one is placing total reliance for L-E fault protection on an RCD, since you won't get enough current through an earth rod to operate an MCB. Given that some people believe that RCDs are much less 'reliable' than MCBs (I'm not sure how they can know
), that's something to think about. Of course, if the house is also (different) TT, then there's no issue - since you're going to be totally dependent on RCDs for L-E fault protection, whatever!
As I say, its w-section and about 1mm. Ive not run the verniers over it but its certainly less than 2mm.
You could, of course, always slip in little scraps of (1-2mm thick) metal (or something) under the clips, to bring total thickness up to ≥2mm.
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