Patch-cord Bend Radius Testing Analysis

This white paper contribution is part of a two part contribution on bend- radius analysis for patch cords that was submitted and presented at the March 2nd 2000, EIA/TIA, TR 42.1 committee meeting in Orlando, Florida. The contributions for testing and field analysis of bend radius provided the support for the TR 42.1 committee to provide a two-third vote to adopt a one times (1x) the cable diameter for UTP patch cords, bend radius in the future 568-B.1 standard. This new standard is to be ratified by the end of this year.

Patch-cord Testing

Patch-Cord Testing Series

Patch-Cord Sampling
- A total of 12 different manufacturers of patch cord assemblies were selected.
- A sample of 3 cords, 10 foot each (Category 5e) from each of the 12 manufacturers was provided (for a total of 36 cords).
- Ten of the manufacturers (30 cords) were purchased through distributors. - Two of the manufacturers (6 cords) were donated directly from the manufacturer.
- Of the original 36 patch cords, one cord failed due to open pairs on the patch cord assembly's plug. This provided for a total 35 cords to test and analyze.
- Of the 35 cords tested to Category 5e patch cord, Return Loss specifications, 8 failed the controlled test (no bend).
- The 8 failed and the 1open pair assembly cord accounted for a 25% failure rate of patch cords coming out of the factories.

Two Bend Patch-cord Testing Series

Patch Cord Testing Procedure

Using the DCM PCT-350 System, which includes an automatic balanced switching device with a high-frequency interface combined with a HP 8753-E network analyzer and computer, Return Loss was measured to the Category 5e (568-A-5 standard) for patch cords.

A jig was used with two, 2-inch mandrels (1-inch radius - 4 times the cable diameter) based on 0.25-inch maximum size diameter for UTP-four pair patch cables. 0.5-inch mandrels (.25 inch radius) were used to measure one times the cable diameter. All the bending was performed in a set of two (180-degree bends) on each patch cord under test.

The following measurements were taken and recorded in plots 1 through 4 after the cords were secured in place. All 35 patch cords were tested individually in each of the four measurement states (below) for a total of 140 tests.
- Control measurement - no bends (measurement #1, plot 1)
- Two, two inch mandrels (measurement #2, plot 2)
- Two, 0.5 inch mandrels (measurement #3, plot 3)
- Two, collapsed points (measurement #4, plot 4)

After all cords were tested under the four different measurement states, they were combined into comparison analysis -- plot #5.

Lowest Margin from CAT5E Patch-cord Limit Line (MHz)
Average Worst Case Margin.from CAT5e Patch Cord Limit Line

Patch-Cord Testing Series Conclusion

As indicated in the summary analysis (plot #5) the fully collapsed cords measured a 1.14 dB loss (average) when compared against the control cords (average). This indicates that this measurement state (fully collapsed) must be taken into consideration during patch- cord testing procedures.

Supporting Contribution

TIA TR-42.7.2 - Patch Cord Minimum Bend Radius, #028 by CommScope

Recommendations for Patch Cords Testing

To protect the consumers from field installations practices provide that fully collapsed cord test be inserted into the Mechanical Handling Stress Test as defined in the 568-A-5 standard (printed below).

G.8 Mechanical handling stress test Modular patch cords shall comply with the return loss requirements of 6.3.1 after each step listed below. For all test conditions, a maximum 150 mm (6.0 in) of undisturbed cable shall be allowed to enter the test fixture at both ends.

1. Test the patch cord uncoiled.
2. Loop the cord (following the natural cable lay) into a 150 mm (6 in) diameter loop, up to ten loops total, and test.
3. Compress the coil into an ellipse and fully collapse at the bending points in the ellipse and test.
4. Rotate one end of the coiled ellipse by 180 degrees (following the natural cable lay) to form a figure eight in the non-conductive trough and test.

Four Bend Channel Testing Series

Channel Testing Series

Utilizing the same testing equipment as used in the previous Patch Cord Testing Series and selecting previously profiled cords, two cords (10 ft.) were inserted into a 90-meter basic link to establish a channel. Although the patch cords were inserted into a channel, we also provided basic link measurement limits when testing for comparison. The basic link limits are more stringent (after 20 MHz) for RL than channel.

A total of five different channels were constructed from the same 90-meter link utilizing ten different cords that were pre-qualified (profiled). A jig was used to provide controlled bending (180-degrees) two cords installed in the constructed channel. A total of four bends was applied (two on each cord) and measurements taken to Category 5e channel and basic link requirements.

The following measurements were taken and recorded in plots 1A through 4A after the cords were secured in place for each of the five channels.

- Control measurement - no bends (measurement #1A, plot 1A)
- Four, two inch mandrels (measurement #2A, plot 2A)
- Four, 0.5 inch mandrels (measurement #3A, plot 3A)
- Four, collapsed points (measurement #4A, plot 4A)

After all five channels were tested under the four different measurement states they were combined into comparison analysis -- plot 5A.

Lowest Margin From CAT5E Channel Limit Line (MHz)

Channel Testing Series Conclusions

The channel limit is the most important factor when testing components of a system. Due to the fact that the sum of all individual components in a channel do not add up to the performance of that channel, it is imperative that the channel be tested with the cords used for that channel. This will reflex the interaction and provide the true performance of that channel.

The effects of return loss on the degree of bending patch cords in a channel has no direct correlation to performance. As indicated in the testing of four, one-inch radii (2-inch mandrels) inserted in a channel was the worst in performance of the different degrees of bends applied and still had a 1.18 dB margin over the more stringent Category 5e basic link limits when tested in a channel.

Average Worst Case Margin.from CAT5e Basic Link Limit Line

Patch Cord Channel Recommendation

Provide a minimum bend radius, under no load conditions of one times (1x) the cable diameter for 4-pair UTP patch cords.

TR 42.1 Committee Response

The committee ratified the above recommendation by two third votes in the favor of a one-time the cable bend radius (1x) for UTP patch cords.

See White paper - TIA/EIA TR-42.7contribution #448 for Patch-cord Field Analysis
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