These cables are used in communication systems as following construction :
1- Layer, for general use, including two cables for installation in customers’ premises where good appearance is required.
2- Unit , of 20-pair , including a 1.38 mm diameter insulated earth conductor , for use with customer distribution schemes.
3- Unit , of 16-pairs , for use with the binary number system.
4- Unit , of 30-pairs , for use with PCM systems. and are manufactured in acc. with British TELECOM CW1308