An interesting observation is that if one did 'throw away' the OSG, and also the informative' Appendices of BS7671, then quite a lot of things that many people 'swear by' (as if they were regulations) would be lost - things like diversity guidelines, voltage drop guidelines, the question of what can be connected to an unfused spur from a ring final, etc. etc.
I am.
I don't know either, but what is clear is that BS7671 says virtually nothing about it (even in an 'informative' Appendix) beyond mentioning that the concept 'may be applied' in appropriate circumstances. However, many people (including you and I) more-or-less 'assert' things such as "A total maximum cooking appliance load of X amps may be regarded as Y amps" - without having any idea as to who decided that (and how 'authoritative' those ' they' may be).
In terms of detail, only really in 'informative' Appendices. In particular, the much-quoted (often as if they were 'regulations') 3% and 5% figures are only guidelines in an 'informative' Appendix. BS7671 itself says nothing specific about spurs from ring finals (other than that they are allowed to exist) and, as you know, it is perfectly possibly to design some spurs that would be 'in violation of' the guidelines of Appendix 15 (which, again, people often 'assert' as if they were regulations).
I think that can probably be trumped for 'ridiculousness' ...
It seems that a lot of what the OSG says about spurs is actually a prose version of the guidance in Appendix 15 of BS7671.OSG said:
The concept obviously has (and is conceptually totally reasonable), as undoubtedly have some guideline figures/calculations (which generally 'work'), but where do they come from? If you or I were, hypothetically, having to justify our use of a 'standard' diversity calculation (e.g. in a hypothetical Court of Law), we would have nothing go cite in our support other than the OSG, would we?
As I said, nothing particularly specific there. In the absence (which I imagine will usually be the case) of a 'relevant product standard', the only regulatory requirement is that VD should not impair the safe functioning of equipment - and I think you'd struggle a bit to think of (m)any items of equipment which would become 'unsafe' because they were supplied with a lower-than-intended voltage! For actual guidance (in particular, the oft-cited {'as if they were regulations} 3%/5%), 525 refers one to ('informative') Appendix 4.
Quite so. Ditto Appendix 15.
That's what I said in my last post. However, how often do we hear people 'asserting' that some proposal related to unfused spurs is "not allowed" (because it 'violates' something which Appendix 15 says, or sometimes merely because Appendix 15 does not even mention the possibility amongst its 'examples')?
I don't think that anyione has suggested that it does. It's certainly true that, when there is a difference, the OSG is almost invariably more restrictive/'conservative' than BS7671 - such that following OSG guidance will result in compliance with BS7671.
The general concept of "I did it because that's what we've always done and it has always seemed to work" is not necessarily the soundest concept in existence. Given that the OSG contains quite a few things which (albeit usually erring on the side of conservatism/safety) are difficult to make sense of, I'm not sure how much confidence one can have in anything it says, particularly things which are not justified by explanations or reference to 'sources'.
Maybe anybody truly competent to do them would know.
In the absence of some external guidance (from those who had undertaken the tests etc.), unless they had personally undertaken extensive tests/investigations (which no individual will have done), there is no way that anyone could "truly" know what diversity calculation was appropriate.
In situations such as we are discussing, individuals cannot be expected to determine for themselves what calculations are appropriate, and what constants should be used for those calculations. Even if an individual somehow decided that an appropriate way of calculating after-diversity current in a particular situation was "the first X amps plus Y% of the rest), there's no way that they could determine for themselves the appropriate values of X and Y without doing extensive (and totally unrealistic) experimentation
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