NEC 501.10(B)(5) Wiring methods for class I, div 2 states cable type TC is permitted to be installed in cable tray. That means 500kcmil wire must be a three conductor cable (3/C) if it run in tray through a hazardous C1D2 area. The question that has been asked and I am trying to find an answer for is - "why can't type CT rated wires be used in the same application provided proper termination seals are used?"
It seems that using individual wires would be less likely to propagate gas from one area to the next should an event happen where the gas could enter the cable. Installing large single conductors is easier than a large multi-conductor in nearly any circumstance.
I have asked cable manufacturers and they point to UL, I asked UL and they pointed to NFPA.
Can anyone tell me why type CT is not permitted or should not be permitted in C1D2 hazardous areas?