Rating Factors
   The current rating mentioned in above tables based on ambient temperature 30°C in accordance with IET Wiring regulations for Electrical Installations,         BS 7671.

Rating Factor for variation in Ambient Air Temperature.

  Air Temperature (°C)           25 30 35 40 45 50 55 60
  Rating Factor               1.02 1.00 0.96 0.91 0.87 0.82 0.76 0.71

Rating Factor for one circuit or one multicore cable or for group of circuits or a group of multicore cables.

 Arrangement

 (cable Touching)

                                 Number of Circuits or Multicore Cables
1 2 3 4 5 6 7 8 9 12 16 20

 Bunched in Air,   on a surface,   embedded or   enclosed

1.00 0.80 0.70 0.65 0.60 0.57 0.54 0.52 0.50 0.45 0.41 038

 Single layer   on wall or   floor                

 1.00                         0.85  0.79   0.75  0.73  0.72    0.72    0.71  0.70  0.70  0.70  0.70

 Single layer   multicore on a   perforated   horizontal   or vertical cable   tray system

 1.00 0.88 0.82 0.77 0..75 0.73 0.73 0.72 0.72  0.72  0.72  0.72

 Single layer   multicore on   cable ladder   system or   cleats  etc.

 1.00 0.87 0.82 0.80 0.80 0.79 0.79 0.78 0.78 0.78 0.78  0.78