Indeed - and I think that, contrary to what you seem to have been implying, giving a free copy of BS7671 to those sort of people would not make one iota of difference to the way they behaved. Those who are at all concerned about doing things properly will already have a copy or, more likely, will have one of the (very many) cheaper publications (or even free on-line material) around which give a reasonable insight into the most important principles of BS7671.
It says nominal value of fuse and breaker.
It does, indeed, but as I wrote ....
Do you disagree? As I see it, those tabulations are essentially the same as those in App 4 of BS7671 (for whatever installation method), but with the currents 'rounded down' from actual CCC to the next higher common 'nominal fuse/breaker rating', aren't they?
If they are talking about re-wireable (like BS3036) fuses, one has (at least, per BS7671!) to apply a 0.725 correction factor to take into account the fusing current of such devices being relatively much higher (in relation to rated current) than is the operating current of an MCB. (a Type B MCB has to trip within an hour with a current 1.45 times it's rated current; with a BS3036 fuse, it's more like 2 times the rated current).
Don't you mean rounded down? 4mm seems particularly low, though.
Sorry, yes, - it's Saturday evening , so I'll blame the merlot! ... I'll edit it!
As I said, they're quite similar to BS7671 Method 100/102 figures - that's 27A CCC (per BS7671) for 4mm² - so 25A is surely the MCB size it has to be rounded down to (and 20A not far off the corresponding 3036)?
Quite - but, as I said, with the 'rounding down' the figures are pretty compatible with BS7671 Methods 100/102/B. That could just be a co-incidence, but it may actually relate to what the table heading would/should have said about installation method!
They would all appear to be consistent with Method C.
So the only reason, from my understanding, is that a 20amp re-wire able fuse would hold an over current condition longer than an MCB. MCBs start their trip curve around 125%, correct?
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