I have always thought they would, however, if the maximum Zs is wrongly adjusted so that they don't have to, then they don't have to - but this would not be using the correct values.
I suppose it depends 'which book' they use.
If, as you would presumably like, they used only BS7671, it presents them with a Table entitled "Maximum Zs values". Whilst I'm not saying that it excuses them, I can 'understand' that if they make a measurement (with conductors at roughly ambient temp) and get an answer less than the tabulated 'Maximum Zs' figure, then they could well assume that the circuit is therefore 'OK' ('compliant').
I might be wrong, but I strongly suspect that this is an issue which is not all that widely understood/realised (or thought about). There have been lots of discussions (here and elsewhere) about 'maximum Zs', particularly around the time that all the figures changed because of the introduction of Cmin. In those discussions, the (explicit or implicit) gist is commonly that if the measured Zs of a circuit (measured either 'directly' or as R1+R2+Ze) is less that the "Maximum Zs" figure tabulated in Table 41.3, then the circuit is 'OK'. However, in reality the measurement [either of Zs or (R1+R2)] will nearly always have been undertaken with a conductor temperature considerably less than 70°C - so a measurement which is only a little less than the tabulated 'Maximum Zs' may well relate to a circuit whose Zs will not be OK if (as one has to assume) the conductor temperature were 70°C.
As I've said, there is 'no excuse' for making this mistake, but the risk of that happening would probably be reduced if the title of Table 41.3 were made a little more clear - since it's quite easy (even if 'not excusable') to assume that "Maximum permissible Zs" means "Maximum permissible measured Zs". The alternative (which is what the OSG seems to be attempting to do) is to tabulate the "Maximum permissible Zs when measured with conductors at ambient temp".
I don't think BS7671 does quote figures for conductors at 70°. .... For example B32 MCB is 1.37Ω; i.e. 230 / 160 x 0.95.
OK, I didn't use clear enough language (although I assumed that you would understand my point). As you say, Max Zs figure does not depend on temperature, so that the tabulated 'Max Zs' figures do not relate to any particular temperature. Hence, as you go on to say ...
... It is the conductor resistance which alters and must be adjusted for the actual circumstances - as we have been explaining.
Obviously all true - but, as above, errors could be reduced by one of the approaches I mentioned. Although, yet again, it's not an excuse, if one "measures Zs" and then refers to a table entitled "Maximum Zs", it's not hard to see what can go wrong.
That some think it necessary for publications to adjust that which cannot be adjusted so that everything is at the worst case scenario for the ignorant (OSG) is not, in my view, the correct way to do things.
Yep, but you refer to an ideal world. In the real world, all human beings are fallible, and of varying degrees of intelligence, knowledge and reasoning ability, so it always make sense (in any field or walk of life) to anticipate what one can of 'predictable human errors' and do what one can to reduce/minimise the risk of them occurring.
Kind Regards, john
However, as above, if they had presented figures for, say 20°C, then I think that I would probably regard that as more 'appropriate' ('idiot proof') than BS7671's 70°C figures.
