Incorrect Cable Component Use Leads to 76% Pass Rate in Category 5 Cable System Engineering Acceptance

Network analysis

1. Symptoms

A well-known systems integrator contacted us today to report a serious quality issue. They had used Category 5e cable products from a prominent cable manufacturer for a 15,000-point pilot project. Each cable link in the wiring system had undergone rigorous on-site certification testing, and all passed. They were preparing to settle the project payment when, a week ago, the project owner suddenly raised concerns about the integrator’s on-site certification test reports. The reason given was that the cable standards on the test report did not match the type of cable used. The integrator rechecked all of the contractor’s test reports and believed that the parameters were fine. The test report had used North American Category 5 cable testing standards, while the owner insisted that the corresponding Category 5e cable standards needed to be used for certification testing to be valid. The integrator then instructed the contractor to retest using Category 5e cable standards, resulting in approximately 9% of the links failing and 15% of the parameters triggering alarms. This project was managed by the integrator, while the cabling work was subcontracted to another contractor.

2. Diagnostic Process

We were invited to the site immediately and randomly selected 100 cable links for testing. The results were consistent with the contractor’s retesting, indicating a significant quality issue. A statistical analysis of the test parameters revealed that essentially, it was a combination of Near-End Crosstalk (PSNEXT), Power Sum Alien Crosstalk Ratio (PSACR), and Return Loss (RL) that were failing. The maximum deviations were -1.5dB, -1.0dB, and -2.8dB, accounting for 9% and 15% of the parameters near the standard’s edge. Because these deviations were within the instrument’s error limit, the test parameters were flagged as alarms. We initiated the DSP-4000 cable analyzer’s automatic diagnostic function, and the instrument pinpointed “fault” points at the connectors of the tested links, at the ends of the horizontal cable. The instrument recommended checking or replacing the connectors. We replaced them with Category 5e connectors we had on hand, and retested, resulting in “PASS” readings. We then consecutively replaced connectors on three failed links provided by the contractor and retested them. Two of the three links remained failed, while one transitioned from a failed status to passing. This indicated that the contractor had used Category 5 connectors, not Category 5e connectors, with their Category 5e cables. The data provided by the contractor was that they used Category 5e cable throughout, but the connectors were “possibly” Category 5 – accurate information was unclear.

3. Conclusion

Generally, Category 5 cable field testing standards should be used for the certification testing of Category 5 systems, not Category 5e cabling systems. Many contractors used Category 5 cable testing standards for Category 5e projects because, at the time, there were limited international standards for Category 5e during construction. Manufacturers claimed that their products exceeded the upcoming Category 5e standards, so, as long as there were no obvious issues with the construction process, link parameters should be passing. Another reason was that most contractors practically used Category 5 system field testing standards for a period. Consequently, this project also used Category 5 cable standards for field certification testing, as the acceptance testing procedure with the customer didn’t specify the specific standards to be used. After the project ended, the customer only “accidentally” discovered that the test report followed North American Category 5 cable standards, which didn’t align with their Category 5e cable system, so they raised objections and requested retesting according to Category 5e standards. We know that the North American Category 5e cable field certification testing standard was officially published on January 27, 2000, while this project began before that date. Thus, the contractor chose to use North American Category 5 cable standards for acceptance testing. The test results were naturally 100% passing. If the contractor had used Category 5e components throughout the cable system – both cable and connectors – then when the customer requested retesting, the pass rate should have remained close to 100%. Unfortunately, the contractor had a misunderstanding about Category 5e cable systems and intentionally or unintentionally used Category 5 connectors in their Category 5e cable links. As a result, when the customer requested retesting according to Category 5e standards, approximately 24% of the links had problems.

Why wasn’t it 100% of the links with problems? This was because the “Category 5 connectors” combined with “Category 5e cables” should theoretically perform slightly better than a “pure Category 5 system.” Additionally, Category 5 connectors had some margin in their design and production parameters. Therefore, in this project, 76% of the links passed the Category 5e cable standard field certification testing. Nine percent of the links couldn’t meet the link parameter requirements, and 15% of the link parameters were in the “gray area” at the edge.

4. Diagnostic Recommendations

We won’t delve into the reasons for why the contractor used Category 5 connectors for the installation instead of following the design specification and using Category 5e connectors. Based on the results of the on-site testing, rework due to this choice is inevitable. Luckily, the cables used in this system are Category 5e cables, and the rework is generally limited to the connectors at the ends of the horizontal cables.

We recommend that the integrator instruct the contractor to replace all Category 5 connectors with qualified Category 5e connectors, even for the 76% of links that previously passed and the 15% on the edge. This is necessary to ensure the Category 5e cable system maintains its qualification for a considerable period (e.g., during the 15-year warranty period).

5. Afterword

Three weeks later, the integrator informed us that all connectors had been replaced, and the system passed acceptance testing according to North American Category 5e cable field certification standards. This concluded the project successfully, but the integrator incurred significant costs. Apart from the connector replacements, they also had to pay 120,000 RMB in compensation to the customer (an average of 8 RMB per cable link).

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