Another shower upgrade query

[JohnW2]

Although I agree with this, there are no strict rules on the definitions and as everything is referenced to something which in iself has no legal standing the whole thing is on a sticky wicket.

Indeed. As I think most of us are agreed, it seems very unsatisfactory that EICRs, particularly the coding, are so reliant on individual discretion/judgement.

A cable running at ~120% of its absolute loaded rating (many areas are still >240V) is an overheating risk and therefore potentially a hazard risk.

Strictly true. However, as I said, the tabulated CCCs ('absolute loaded ratings') we work with take into account the characteristics of MCBs - such that it is deemed that Method C 4mm² T+E will not come to any harm (or represent any hazard as a result of carrying about 41.8 A continuously, or about 53.6 A for an hour - so, even if one assumes a 240 V supply (which we are not expected/required to do for design purposes), it is extremely hard to believe that the cable would come to any harm (or represent any hazard) as a result of carrying about 43.75 A for the duration of a shower.

So, as I said, I would personally struggle to regard that situation as "potentially dangerous and requiring urgent remedial action" (i.e. C2), and would (again personally)) regard it as fairly ridiculous to code it as C1 - not the least because that would go against the 'spirit' of C1

 

[EFLImpudence]

At which of those ratings - 37A, 41.8A, 53.6A) does the cable actually reach 70ºC?

Is it that cables in domestic premises never reach the 70ºC unless something has gone extremely wrong?

 

[JohnW2]

At which of those ratings - 37A, 41.8A, 53.6A) does the cable actually reach 70ºC?

Who knows? If getting hotter than 70C would harm the cable, one would hope that the answer would be 53.6 A - and, in any event, as often discussed, I suspect that there are some generous 'safety margins' built into the figures we work with.

Is it that cables in domestic premises never reach the 70ºC unless something has gone extremely wrong?

Again, I don't know for sure, but I strongly suspect that what you suggest is probably the case