when looking up current carrying capacities in the 7671 regulations ( IEE ) how would you decide which reference method to use if there where two used in the intallation in question eg if general twin core and earth cable was to run for 10 mtr clipped dirrect and then a further 10 mtr enclosed in a wall?between these two methods the diffrence can be as much as 15 amps [Linked Image]

or is it educated guess time?