IEC 60364-5-52 provides tables of cables ampacity derating factors (in single layer in trays). Highest number of cables is 9 with 6 layers of trays (spaced 300mm or more vertically). Now my query is: Has anybody worked out the derating factors for 2 layers/3 layers/random fill of cables in tray? Why is there a fundamental difference in cable laying conditions between IEC and NEC/NEMA world?
Interestingly, IEC 60364-5-52 Sec. 523.3 says: The appropriate values of current carrying capacity may also be determined as described in IEC 60287 series , or by test, or by calculation using recognized methods. This opens up an window for methods used by research publications or mathematical models.
One thing to be noted: Single layer of power cables results in large number of trays. Now, it is a techno-commercial decision to adopt two or three layers of cables (with larger derating factor) resulting in larger cables, and reduced length of trays.
Interestingly, IEC 60364-5-52 Sec. 523.3 says: The appropriate values of current carrying capacity may also be determined as described in IEC 60287 series , or by test, or by calculation using recognized methods. This opens up an window for methods used by research publications or mathematical models.
One thing to be noted: Single layer of power cables results in large number of trays. Now, it is a techno-commercial decision to adopt two or three layers of cables (with larger derating factor) resulting in larger cables, and reduced length of trays.
