The conductors have been divided into four classes: 1,2,5 and 6. Those in classes 1 and 2 are intended for use in cables for fixed installations. Classes 5 and 6 are intended for use in flexible cables and cords but may also be used for fixed installations.
 Class 1: solid conductors
 Class 2: stranded conductors
 Class 5: flexible conductors
 Class 6: flexible conductors which are more flexible than class 5

cable - classification