derating factor for cable

http://www.theiet.org/publishing/wiring-regulations/index.cfm

Derating factor is the factor by which the current carrying capacity of cable increases.(It actualy decreases as Derating ,by name, suggests and is less than 1).

Yes we need to apply Temp, group ,Laying etc at a time.

I hope u r talking about LT cables. Normally for all types of cables these r applicable.

U can ask for these data from any cable manufacturer, preferably the cables u r using.

thanks