I am not answering your post as I hope Sparx may pick it up and give a better answer. I seem to remember the tables in the OSG were already temperature corrected and were slightly different to BS7671 which may explain things.
I have not got an on site guide yet not sure I ever will I already have 17th so don't need it for exam.
However I was also looking at cable ratings especially the 90 deg C type which there seems a lack of any tables to cover.
I did look at table 4D5 etc. see http://www.ericpalmer.fsnet.co.uk/Table4D5.html if you haven't got book to hand and I was also trying to work out the refusal point.
If I was selecting cable I would always go slightly bigger than required but when someone else has selected it and you think it is under size you need to be sure before engaging mouth and telling them they have go it wrong and there does seem to be a lack of information.
How does the Table 4D5 compare with OSG tables?
Thanks for your thoughts, I can confirm the 4D5 table in regs and OSG are the same.
I can see your train of thought regrading cable sizing as i'm of a similar view.
Especially if the current carrying capacity is at the top end.
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