Patch-cable bend radius a tight issue

From a cable-management standpoint, I find that patch cables with stranded conductors have a more relaxed lay than patch cables with solid conductors, which tend to be more rigid.

Last August, the first addendum to the Telecommunications Industry Asso ciation's (TIA-www.tiaonline.org) TIA/EIA-568B.1 Commercial Building Telecommunications Cabling Standard was published. The addendum, entitled "Minimum 4-Pair UTP and 4-Pair ScTP Patch Cable Bend Radius," does not have a great deal of verbiage, but may have a significant impact on cabling-plant managers' ability to manage patching fields within telecommunications rooms.

Dennis Mazaris, RCDD, played a significant role in the ratification of Addendum 1 to TIA/EIA-568B.1, including presenting test data showing that cabling channels do not necessarily suffer performance degradation from tightly bent patch cables. Mazaris is president of PerfectPatch (www.perfectpatch.com), which manufactures a product by the same name-a patch-cable management device.

We interviewed Mazaris to get his perspective on issues surrounding the TIA addendum and patch-cable management:

CI&M:Please tell us what is specified in Addendum 1 to TIA/EIA-568B.1.

Mazaris: The addendum specifies the minimum inside bend radius for both unshielded twisted-pair (UTP) and screened twisted-pair (ScTP) patch cables, under no-load conditions, meaning the cables are not bearing any weight. For UTP patch cables, the minimum inside bend radius is 6 millimeters (mm), which is 0.25 inches. For ScTP patch cables, the minimum inside bend radius is 50 mm, which is 2 inches.

CI&M:Is this addendum an update to any previously existing standard addressing patch cables?

Mazaris: No it is not. Many people believe that a minimum patch-cable bend-radius of 1 inch had been specified previously. But that radius specification applied to cable in terminated spaces only, and did not apply to patch cables.

CI&M:In many cabling systems, patch cables are used in several places-in the work area from a PC to an outlet; in the telecom room between connecting hardware and network equipment; and, of course, between patch panels in systems that implement cross-connections. Do these specifications apply to patch cables used in all those environments?

Mazaris: Yes, the specifications apply to what are commonly called equipment cables and work-area cables, as well as to cables used between patch panels.

CI&M:Are patch cables constructed differently from cables used in the horizontal, such that they can withstand bending better than horizontal cable?

Mazaris: That question raises an interesting point. Most patch cables incorporate stranded copper conductors, whereas horizontal cable incorporates solid conductors. However, TIA/EIA-568B.1 allows for the use of solid conductors in patch cables, so patch cables are available with stranded or solid conductors. The patch-cable bend-radius specifications apply to cables regardless of whether they include solid or stranded conductors. From a cable-management standpoint, I find that patch cables with stranded conductors have a more relaxed lay than patch cables with solid conductors, which tend to be more rigid.

CI&M:The TIA is not far away from having all the T's crossed and I's dotted on the Category 6 standard. Will these patch-cable specifications apply to Category 6 systems?

Mazaris: Yes, Category 6 systems will be subject to the 6-mm minimum inside bend radius for UTP and 50-mm inside bend radius for ScTP specifications.

Dennis Mazaris, RCDD, is president of PerfectPatch (www.perfectpatch.com).