not sure what you are asking or hoping to achieve, presume you are looking at rating factors table 4B1, your cable is never going to run at lower than 25'C with any sort of load.
Are you trying to justify use of too small a cable size?
more info. plz
Having looked at the ERA tables, I can get the 20 deg figure now. No problem.
However to answer the question, I am, as you surmise, trying to size a cable.
The area is fully air conditioned to be between 18 and 20 degrees.
Including the plantroom.
Another issue was using XLPE or PVC, if using XLPE the terminals on the equipment needed to be rated at 90 deg C, although I can calculate at 90 Deg C run at 70 deg C, which may have over come the problem.
Interestingly, the equipment supplier quoted the terminals to a BS that made them 70 deg C over ambient, therefore at 40 deg C the terminals would be rated at 110 deg C - seems unlikely!
Have resolved the problem now.
Thanks for your help.
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