Rating factor for variation in Ambient temperature

Correction Factor for groups of Cables

Arrangement( Cables touching)	Number of circuits or multicore Cables
Arrangement( Cables touching)	2	3	4	5	6	7	8	9	10	12	14	16	18	20
Bunched in Air, on a surface, embedded or enclosed(Methods A to F)	0.80	0.70	0.65	0.60	0.57	0.54	0.52	0.50	0.48	0.45	0.43	0.41	0.39	0.38
Single layer on wall or Floor (Method C)	0.85	0.79	0.75	0.73	0.72	0.72	0.71	0.70	0.70	0.70	0.70	0.70	0.70	0.70
Single layer multicore on a perforated horizontal or vertical cable tray system (Methods E&F)	0.88	0.82	0.77	0.75	0.73	0.73	0.72	0.72	0.72	0.72	0.72	0.72	0.72	0.72
Single layer multicore on cable ladder system or cleats etc. (Methods E & F)	0.87	0.82	0.80	0.80	0.79	0.78	0.78	0.78	0.78	0.78	0.78	0.78	0.78	0.78

(Ref. IEEE wiring regulation Seventeenth edition)