Flexible cables in stud walls

Welcome to the forum - here is one opinion, others may follow.
Well the tables in the regs are only a guide to the most common cases, as there are a more or less infinite range of things that can be done, and in any case  are subservient to any more detailed cable makers data, ERA reports etc. So if the makers publish anything more relevant, try to use that.

But the physics of electricity heating  up cores of a given cross section of copper, and then more or less obstructing the escape of the heat and estimating a temperature rise are not that variable. As a first go you could look at the de-rating of another cable of more or less the same geometry, say 2.5mm2 solid core,  in a similar environment, and say

'ah between free air and in this location the rating drops by XYZ percentage - I have assumed a similar percentage de-rating on this other cable for which I only have a free air rating.' And then if you are nervous, round to the nearest % more in the direction of safety...

Equally, 13A sockets on 2.5mm of almost any kind are unlikely to struggle any more than the same load on twin and earth, as the saving grace is actually that plug-in  loads tend to be very intermittent and most of the time a lot less than 13A anyway.

If you know that multiple 13A loads for a long time are likely - perhaps its in a burger catering van with hotplates, toasters and tea urns.. then a harder look is needed.

If the cable has been in use for it bit, look at it - does it look cooked, has the insulation blooped or gone brown and cracked in the heat ? Unless it has, whatever number you derive, it is fair to say it is not immediately dangerous for the existing load profile.  (I have found sockets on 1mm T and E, but only supplying a couple of cash registers and a light, so as the MCB was 10A, we let it go with just a recommendation that the sockets should not be used for heavier loads.)
Reverse also true- if it does look heat damaged, even if the sums say it should not be, something needs to be changed, fatter cable, splitting the loads into multiple branches, improved cooling, or if only burnt at the last inch, bigger back box and not the cheapest socket with the thinnest crummy terminals.

Mike

(In the report if worried you could put your calculated 22A, 20A or 18A or whatever and a little *, where somewhere else it says *= estimated value for non standard situation, just  to show it is not an officially endorsed figure )

Welcome to the forum - here is one opinion, others may follow.
Well the tables in the regs are only a guide to the most common cases, as there are a more or less infinite range of things that can be done, and in any case  are subservient to any more detailed cable makers data, ERA reports etc. So if the makers publish anything more relevant, try to use that.

But the physics of electricity heating  up cores of a given cross section of copper, and then more or less obstructing the escape of the heat and estimating a temperature rise are not that variable. As a first go you could look at the de-rating of another cable of more or less the same geometry, say 2.5mm2 solid core,  in a similar environment, and say

'ah between free air and in this location the rating drops by XYZ percentage - I have assumed a similar percentage de-rating on this other cable for which I only have a free air rating.' And then if you are nervous, round to the nearest % more in the direction of safety...

Equally, 13A sockets on 2.5mm of almost any kind are unlikely to struggle any more than the same load on twin and earth, as the saving grace is actually that plug-in  loads tend to be very intermittent and most of the time a lot less than 13A anyway.

If you know that multiple 13A loads for a long time are likely - perhaps its in a burger catering van with hotplates, toasters and tea urns.. then a harder look is needed.

If the cable has been in use for it bit, look at it - does it look cooked, has the insulation blooped or gone brown and cracked in the heat ? Unless it has, whatever number you derive, it is fair to say it is not immediately dangerous for the existing load profile.  (I have found sockets on 1mm T and E, but only supplying a couple of cash registers and a light, so as the MCB was 10A, we let it go with just a recommendation that the sockets should not be used for heavier loads.)
Reverse also true- if it does look heat damaged, even if the sums say it should not be, something needs to be changed, fatter cable, splitting the loads into multiple branches, improved cooling, or if only burnt at the last inch, bigger back box and not the cheapest socket with the thinnest crummy terminals.

Mike

(In the report if worried you could put your calculated 22A, 20A or 18A or whatever and a little *, where somewhere else it says *= estimated value for non standard situation, just  to show it is not an officially endorsed figure )

Thank you for your reply. 

T