Hothouse wires (of conservatories in sunlight)

[Mega Greg]

Just wondering about the potential heating problems of cables installed on or in the sunlit walls of sunlit conservatories and glass fronted rooms.



One air con company website refers to conservatories saying: "Perhaps the biggest problem is the very fact that they become far too hot in the summer (up to 50 C or 122 F)".
Clearly 20C above the ambient temperature mentioned in Appx 4 but we can also note the view that some surfaces in direct sunlight can get "hot enough to fry eggs".


I then image a situation in which householder A is working in the garden/garage/drive with noisy / dust making machinery which is fed from a sunlit wall while householder B keeps the conservatory doors and windows as closed as possible to keep the noise and dust out.
So far I've just got as far as to note that BS 7671 doesn't have a special location section for glass enclosed spaces in direct sunlight but that Appx 4 'Para' 2.1 admits - "...
The rating factors in Tables 4B1 and 4B2 do not take account of the increase, if any, due to solar or other infrared radiation" – (IR being one relevant form of electromagnetic radiation).
It then goes on to say:
"Where non-sheathed or sheathed cables are subject to such radiation, the current-carrying capacity may be derived by the methods specified in BS 7769 (BS IEC 60287)."
[I don't have a BS 7769. The big colour changing book was expensive enough].


The RCD protection of conservatory sockets would safeguard people from electric shock but I'm wondering about the effects on wiring in sunlight and the types that should be used.

 

[Mega Greg]

Can also note:
522.11.1 Where significant solar radiation (AN2) or ultraviolet radiation is experienced or expected, a wiring system suitable for the conditions shall be selected and erected or adequate shielding shall be provided. Special precautions may need to be taken for equipment subject to ionising radiation.
NOTE: See also regulation 522.2.1 dealing with rise in temperature

Not sure of the reference to significant solar radiation. Locations at latitudes between 50N and 59N (like the British Isles) get similarly effected by the sun.

I'm still wondering about the good British wall. Whether in or out of glazing, would it be classed as a place where solar radiation may have a significant effect on wiring.

 

[johnboy6083]

fair point mate. Its upto us as designers of our installations, to select and install the cable and containment, best suited to the job. When carrying out cable calcs, you derate the cable for an increase in ambient temperature. The only place where i can really see this being a significant problem, is in the top of the conservatory, ie for the lights. I would hide the cable from direct sunlight. 9 times out of 10, a conservatory light would be a sputr from the l;ighting circuit anyway, which meanst that the 1mm or 1.5mm cable will be overated anyway, so i cant see this being a big problem.

 

[oxocube]

All the cable rating tables are for an ambient of 30c (as already mentioned) but also the cables are deemed to be fully loaded and at full temperature, for T&E that's 70c. So 50c in a conservatory is not a problem unless the cables are fully loaded, but I'm sure that would be very unlikely.

I would'nt worry about it.

 

[malcolmsanford]

Greg here in the summer it often gets to 55c for months on end, and I've been down sump pits and tech rooms where the temperature in them as touched 68c and have yet to see any heat damage to PVC cables mate so it's not that much of a concern.

All we do as the lads have mentioned is take into account the loading and ensure a cable will always work at 50% above the normal rating capacity. So often you will see a 16amp MCB with 4mm cable

 

[Engineer54]

Can't get much more of a better explanation than that Malcolm... lol!! The last country to worry about summer heat in a conservatory would be the UK, that has been talking about expected ''Indian Summers'' for the last 10 years. ....Alas they have yet to see one yet.. your lucky to get a week of Sun before the rain clouds start forming again. ...lol!!

 

[Mega Greg]

Greg here in the summer it often gets to 55c for months on end, . . and tech rooms where the temperature in them as touched 68c and have yet to see any heat damage to PVC cables mate

Cheers Malcolm, Perhaps its my imagination that's overheating. I'd thought that there might have been stories of the overheating of cables given how hot walls can get in sunlight and a real call to use thermosetting or fp200 cable. With Johnboy's advice though i'l keep it in the back of my mind.

 

[oxocube]

I've worked in various tropical countries and never seen any problems with over heating due to the sun. But in the uk had a major problem where a fan supplier decided to use small (500x600x200ish) roof mounted control panels made of a clear plastic material, and all the relays, contactors etc melted. They were replaced by steel panels and the problem went away.