A scenario was presented in the recent design erection and verification exam where 3 circuits comprising single core single insulated copper cables were to be installed in pvc trunking and run at 90C. Apart from the difficulty in connecting to protective devices and equipment, such a design is an ill-considered one, I would have thought. 
Perhaps this was just an examiner trying to pitch a different situation from the usual 70C cables that are often the subject of questions but forgetting the obvious issues with running circuits at 90C?