Flexible cables in stud walls

yep, the world is not that precise - the tables say nothing about vertical or horizontal routing but it makes a good few degrees difference if the cable is pre-heated by more cable below it.

Even if the figure was 15A for the headline case, the basis of the tables is  a 40degree rise, to 70C from a 30C starting temperature, after some hours at that load to reach equilibrium. In the UK unless the location is near some heat producing kit, much more than a 25C start is unlikely, and rising to 80 instead of 70 does not explode the cable, it just goes a bit floppy, and gets painful to touch. To reassure yourself drop an offcut in your tea and watch it not melt like butter - or ideally your mate's tea. My point is there is an illusion of precision with the ratings - you may calculate 18A and agonise that the load may  be 20 occasionally- but a lot of other things have to go wrong at the same time to actually cause a real problem, even if your sum ends up being 10-20% out on the current rating.

Mike.

Your point is understood. However, myself being a simple electrician, if anything were ever to go wrong with that bit of the wiring (perhaps resulting in a fire), I don't have the qualifications/experience to be able to be able to argue that I evaluated the flex to be acceptable in that scenario, whereas an experienced electrical engineer can argue their case with more gravitas, and be accepted by authorities more readily than I. I recal reading a post on the forum some time ago that perhaps unfairly said that electricians seem to think that if a cable carries more than an amp above its Iz/It, it'll burst into flames, whereas engineers know better. I don't believe we do think that, it's more that we have to go by stated values because we're not qualified to make allowances in ccc that differ from those provided.

T.  

Your point is understood. However, myself being a simple electrician, if anything were ever to go wrong with that bit of the wiring (perhaps resulting in a fire), I don't have the qualifications/experience to be able to be able to argue that I evaluated the flex to be acceptable in that scenario, whereas an experienced electrical engineer can argue their case with more gravitas, and be accepted by authorities more readily than I. I recal reading a post on the forum some time ago that perhaps unfairly said that electricians seem to think that if a cable carries more than an amp above its Iz/It, it'll burst into flames, whereas engineers know better. I don't believe we do think that, it's more that we have to go by stated values because we're not qualified to make allowances in ccc that differ from those provided.

T.