How many times have you picked up a trade magazine and seen beautiful advertisements, detailing a full rack of patch panels with every patch-cord management trimming? The patch cords (not too many, of course), plugged into these panels, are routed, oh so elegantly, in the patch-cord management system. They have such a sweeping bend radius, so perfect, looking like someone took a protractor and drew them in place! In bold print you can read the words: "Meets TIA/EIA-568-A or ISO/IEC 11801 bend-radius requirements."
You find yourself saying: "I couldn't get my patch field to look that good if my life depended on it. I must be in clear violation of the standards." Before jumping to conclusions, it is important to review the standards on UTP and ScTP patch cords.
The bend-radius requirements, as stated in the TIA/EIA-568-A standard, section 10.6.3.2 Cabling Practices for UTP (and, by extension, ScTP indicated in 10.2.1) horizontal cable, reads: "Also, in spaces with UTP terminations, cable-bend radii shall not be less than four times the cable diameter for horizontal cable."
This applies to termination on the back of the patch panel (see figure 1) where the horizontal cables terminated and bend-radius stability occurs. There is no bend-radius requirement for patch cords in the TIA/EIA-568-A standard.
In the ISO/IEC 11801, the patch-cord bend radius is included, as set forth in clause 9.1.6-Installation Practices and 8.1 table 15 (line 1.12) mechanical characteristics of 100 ohm and 120 ohm balanced cables: "The minimum bending radius of installed horizontal cable if four ('f.f.s.,' for further study) times the outer cable diameter."
Since there has not been adequate data presented for patch-cord bending radius, the international community has elected to use 'f.f.s.,' which means it is not a requirement for conformance to this standard, only a suggestion.
Now that we have reviewed the standards, let us look at why it would be hard to impose a requirement for patch cords. The primary factor is bend-radius stability, which is the patch-cord radius' resistance to change in its environment, typically dynamic at the patch panel.
Bend-radius stability is predominant at the back of the patch panel (see figure). This is where the four times the outer diameter rule of the horizontal cable applies. Upon initial installation, very few changes are made that could affect bend-radius stability.
At the front of the patch panel, where patch cords are utilized, bend-radius stability does not occur. Typically, the patch field is in a state of flux due to moves, adds, and changes. This state of flux is high considering that the churn rate of companies can be higher than 40% per annum.
While the standards do not address the bend radius of patch cords, neither do they advocate the kinking of patch cords, which can lead to signal degradation in copper and broken glass in fiber patch cords. The subject of bend radius is one of the many topics that will be tackled in the TIA/EIA TR 41.8.1 (authors of 568-A) installation requirements task group, chaired by BICSI's Standards Representative, Donna Ballast, RCDD. This task group was formed to write the installation and design requirements for the future 568-B standard.