Using Unused Wires in a Network Cable for a Telephone
Last updated: 10/24/03

Q. Can one use the unused wires in a network CAT 5 (and 5e, 6) cable for a telephone connection?

A. The wires in a network cable should not be untwisted more that 1/2" for CAT 5/5e cable and 1/4" for CAT 6 cable. Furthermore, separation of pairs of wires from the other pairs should be minimized as the geometry of the overall cable is important for performance. A network cable should not be bent sharper than 4 times it's diameter. If you are in the US, the ring voltage on the telephone line will probably disrupt the network. In otherwords, I don't recommend it. If the network cable is not going to be used for networking, A four wire, telephone RJ-11 plug can be plugged into an eight-wire RJ-45 jack and the RJ-11 plug contacts will match the unused wires (10/100BASE-TX network, not 1000BASE-TX) in the network cable, if the jack is wired correctly. If it isn't wired correctly and a computer, etc. is connected at the other end, one can expect to see smoke at the other end. I used CAT 5 cable for the telephone lines going to my shop/office, but the cables are terminated with 4-wire RJ-11 telephone jacks and are not shared with my network. One can put four, 2-wire telephones on one 8-wire CAT 5 cable; however the ring voltage may occasionally disrupt any dial-up MODEMS using the same cable. I've seen that happen on 120 foot cables. Larry