Maybe, but it's totally logical. It may not even require any significant changes in the regs - can you remind me where it mentions the 0.725 factor? It is just possible that it is opart of a general statement about 'overload protection characteristics' that would extend to the situation in which there was deemed to be no need for overload protection at all. However, all of this obvioulsy depends upon someone deciding that overload protection is not needed - something which, as I've said, I regard as a ratheer iffy concep.Ooooh! That, I think, would be far too involved and require sub-clauses in just about every relevant regulation and table.one should really be able to actually 'up-rate' it, by multiplying by a factor of 1.45 - but try convincing anyone about that!
Indeed. Did I not write very recently that, with a few exceptions (particularly equipment containing electromagnetic components such as motors and relays), people could try to apply the "cannot cause an overload" argument to a high proportion of fixed-wired loads - leaving, as you say, mainly just sockets circuits needing overload protection! As for your figures, if one used that argument then (provided disconnection times and VD requirements were satisfied - which is quite possible), 4mm² (clipped direct) protected by a 50A MCB would be fine. If, by tails, you mean tails feeding a CU, then I'm not sure that would work, would it, since the maximum possible load (without 'overload' of any final circuit) would presumably be the sum of the Ins of all the MCBs/MCBOs - probably usually much too high for 6mm² (about 68A clipped direct, 'without overload protection').[Also, wouldn't/doesn't/couldn't it apply to almost every circuit apart from those with sockets? 12kW showers or 34kW cookers on 4mm² with 50A mcb. 6mm² tails. Are we over-engineering?
What one has to remember is that the CCC tables presented in Appendix 4 of the regs is just one set of a whole family of possible sets which could be produced. We never see the underlying 'parent set', which are the currents deemed to be the maximum current that a can safely carry for one hour. The tables in Appendix 4 have had all the CCCs from that parent set divided by 1.45, to reflect the overload performance of a Type B MCB. We could have another set for BS3036-protected cables, in which the parent set's CCCs had all been divided by 2. However it's easier for the regs to simply tell us to multiply the Appendix 4 CCCs by 0.725 (i.e 1.45/2) if we're using a BS3036. Logically, if there were deemed to be no possibility of overload, a correction for the 'overload performance' of the CPD would not be necessary, so that 'dividor' (relative to the 'parent set') would become 1 (rather than 1.45 or 2) - so that we would just use the 'parent table' CCCs (aka 1.45 times the Appendix 4 CCCs)!
Kind Regards, John