Q: I am trying to find out whether the current tia/eia-568a standard recommends providing any slack loops in an installation of 4-pair Category 5 unshielded twisted-pair (utp) cable. bicsi (Tampa, FL), in its 1995 Tele-communications Distribution Methods Manual (tdmm), recommends 1 foot of slack at the work area and 10 feet at the telecommunications closet (TC). Has this practice changed? I was told that slack loops increase electromagnetic interference (emi), but I am unable to confirm this. Can you help?
Jonathan Betz
Superintendent, Adkins Cabling
Tucson, AZ
A: bicsi`s tdmm (1996), in Chapter 4--Horizontal Cabling Systems, states: "When cable runs are being installed, consider providing additional slack at both ends--the recommended minimum amount of slack at the telecommunications closet is 3 meters (10 ft) and at the outlet is 1 meter (3.3 ft) for optical-fiber cables and 30 centimeters (12 inches) for twisted-pair cables."
tia/eia-568a only addresses installation practices that cabling manufacturers considered critical to the performance and reliability of the link. Slack does not enhance performance or reliability. Leaving cable slack or a service loop just makes it easier for the installer to reterminate the cable in the future. This practice pre-dates high-speed data applications on utp cable. And yes, coiling the cable may increase the effects of emi. The severity of the problem is directly proportional to the balance of the cable. Good cable balance, no problem; poor cable balance, increased emi.
