Physical Differences Between 3.5c & 4c Cable

phycially 3.5 C will have 3 full size conductor and 1 half size conductor for eg 3.5C X 120 sqmm will have 3 cores of 120 sqmm and last one of 70 sqmm. where as 4 C X 120 sqmm will have all the conductor of 120 sqmm. Fourth core generally meant for the neutral..................... U can use any of them depending upon unbalance load i.e single phase loads and harmonics in the system since each of the above phenomena will lead to heating of the neutral conductor.

Same as difference of 34C and 36B breasts.