Technical Bulletin

A recent industry study* performed by PerfectSite Corporation, an international structured cabling consulting firm, has determined that duplex 62.5/125 micron, multimode fiber optic patch cords, which are typically used as interfacing from the data equipment (located at the horizontal cross connect) to the fiber optic backbone, were treated the same as copper patch cords used to interface the horizontal cables into the data equipment. Bending radius of 1/4" or less was recorded in 79% of the fiber patch cord evaluated, compared to 71% for copper. This is due to the limpness of the fiber patch cords construction under study. When tested with 36 manufactured patch cords and 7,200 applications of the PerfectPatch^TM, the PerfectPatch^TM provided a protective bend radius, bend-radius stability, and attenuation losses of less than .25db per patch cord utilizing the PerfectPatch^TM.

When developing a fiber optic backbone and/or horizontal strategy, one should consider the limpness of fiber optic patch cords and congestion in the vertical management system caused by high-density patching. Although fiber has come a long way, there is one consistency about fiber: if you kink it, the glass breaks. And as fiber works its way into more of the horizontal cross connect area and more fiber optic patch cords are being utilized, the more congested fiber management will become - just like it has with its copper counterpart. And it too will need that extra measure of protection to prevent kinking and to manage high-density patching where the accumulation of slack and entanglement of patch cords proves a major problem in the management performance level. This can directly affect the speed with which faults can be identified and rectified in the network, thus directly affecting the system functional performance level.

Upon developing a structured-cabling-system strategy, one must take into consideration the System Functional Performance Level*, which can be broken down into three interdependent components (see figure 1).

• Component performance level - addressed by TIA/EIA-568-A. First line of defense. If a component doesn't pass specifications, the faulty component(s) must be replaced.
  
  
• Installation performance level - addressed by TIA/EIA-568-A and others. Components are manufactured, based on certain installation requirements, and can be tested out in the field, as specified, in accordance with Section 12 of the 568-A for attenuation losses in fiber cabling systems, and TSB67 for UTP cabling systems or other measurable means based on cable and passive components in a structured cabling system.
  
  
• Management performance level - addressed by the Industry. The impact of management on the speed with which faults can be identified and rectified.
  

* "Standards Update: Year of Aesthetics," BICSI NEWS, January 1997

When fiber patch cord is kinked (unlike the copper patch cords which just may suffer signal degradation), fiber is not as forgiving - it breaks. That is why you must protect it at all times from being susceptible to breakage.

By utilizing the PerfectPatch^TM, you eliminate bending as a key factor in broken fiber (glass) (see figure 2).

When a fiber optic patch cord is bent, it induces compression and tension forces on the surface of the glass fiber. This statistically does not present a problem to the integrity of the fiber unless a microscopic flaw is present (see figure 3). These flaws, prevalent on all glass fibers, would have to be large enough and located precisely in the patch-cord bend (see figure 3). Only then could it proliferate when subjected to tensile forces and environmental changes that lead to flaw growth and reduced fiber strength over the life cycle of the fiber. For this to occur in a patch cord with a 1/4" protective bend radius or greater. Corning, Incorporated performed a probability analysis. The findings were based on using a Two-Region Power Law model for predicting crack growth. The calculated failure or probability is 2x10e-6; that corresponds to a two parts per million-failure rate over 20 years (see figure 3).

Due to the ease of testing multimode fiber optic patch cords in comparison to Category 5 copper patch cords, PerfectSite performed tests at its own laboratory using 4 different manufacturers' light sources and power meters. The testing covered attenuation losses in fiber optic patch cords with relationship to bending radius.

Although there are attenuation requirement tests stated for fiber cable and components throughout section 12, "Optical Fiber Cabling Systems" in the TIA/EIA-568-A, the same results in attenuation will occur when bending patch cords. To get accurate bend readings, it is recommended to use a minimum of 100 feet (30.48m) of cable.

PerfectSite elected to perform a simple test that can be easily replicated in the field and which isolates the effects of bending a patch cord.

Take 3 patch cords and connect them as indicated in figure 4, then reference out (0) the patch cord on the power meter. By submitting the patch cord "B" to bends, there will be an increase in attenuation (see figure 5). PerfectSite examined 12 different manufacturers' patch cords (36 total patch cords). Each used Duplex 62.5/125 micron, multimode patch cords. PerfectSite performed 200 applications of the PerfectPatch^TM, 1/4" protective bend radius to each of the 36 patch cords (7200 total applications), recording attenuation losses after each application of PerfectPatch^TM were applied. The results averaged below .25 db attenuation loss per PerfectPatch^TM application at short wavelength 850nm and long wavelength 1300nm. At no time did the results exceed .5 db. This is less than the TIA/EIA-568-A attenuation loss of .75 db per each mated connector pair.

There is a misconception that has hurt the fiber industry. It is the perception that fiber optic patch cords must have large sweeping bends for the purpose of "maintaining bend-radius requirements." This erroneous concept is not practical in the premises environment as an industry study cites:

"Seventy-nine percent of premises patch cords used in backbone infrastructure have 1/4" or less radius."

This tighter radius is due to the natural limpness of the patch cord and the environment effects of a high-density patching with numerous copper patch cords. This has brought manufacturers of fiber patch cords taking conservative approaches to bend radius with no rationale for backup. Until now, there has been no testing on the subject of a non-load-bearing, bend-radius performance of patch cords.

The TIA/EIA-568-A (section 12.4.5) addresses the bend radius of fiber optic cable in the outlet/connector box not the patch cords as follows:

"The outlet/connector box shall have the ability to secure the optical fiber cable and provide for a minimum of 30 mm (1.18 in) bend radius."

The PerfectPatch^TM with its non-load-bearing bend radius complies 100% to the TIA/EIA-568-A standard.

The PerfectPatch^TM brings a lot to the table in any fiber optic patch-cord management system. It eliminates slack and entanglements. The PerfectPatch^TM provides a protective bend radius, so that the glass in a patch cord does not break. It ensures bend-radius stability and increases the total system functional performance level by improving the management performance level. The PerfectPatch^TM is 100% TIA/EIA-568-A/TSB72 compliant.

PerfectPatchTM Part Number PP-350 PerfectPatchTM PP-350 is the only product in the market that can reduce patch-cord slack, the #1 problem with patch-cord management. It is also the only product to provide protective bend radius with bend-radius stability and non-load-bearing radius (KinkGuardTM) at Fiber Optic performance levels. This product is proven to increase patch-cord performance, management, and aesthetics.