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Cabling Mistakes #2 and #3: Neglecting Marginal Test Results and Parameters

Mark Mullins

While the smart people who install, test and certify network cabling plants know the importance of meeting standards performance parameters and ensuring application support, even the best of us can make mistakes that adversely impact the bottom line and customer satisfaction.

Let’s take a look at the #2 and #3 Dumb Things that smart people do when testing network cabling systems— Neglecting to agree upon marginal test results upfront in writing and failing to specify all test parameters to be tested.

A Marginal Pass is Still a Pass

Back in the days of category 5, marginal passes were rarely seen due to the fact that the components were well ahead of their time in terms of performance. But those days are long gone. Today's category 6A components specify a much higher level of performance that is more difficult to meet. Everything from marginal performance of the components themselves, to installation practices and even the quality of the test equipment can be enough to push the results into the marginal pass region, which on today's standard-compliant test equipment is indicated with an asterisk (*).

Despite the appearance of an asterisk next to your test result, TIA and ISO/IEC standards dictate that any marginal pass is still considered a pass and therefore compliant. The standards specifically state that a parameter shall be marked with an asterisk when the result is closer to the test limit than the measurement accuracy published by the field tester manufacturer. That clearly indicates that tester accuracy plays a role.

By selecting an industry-compliant tester like the DSX 5000 CableAnalyzer™ that offers repeatable, exceptional accuracy, you can minimize marginal test results. And beware of any tester than allows you to disable the asterisk and hide marginal results. This makes the tester non compliant; not to mention that it can put your reputation and business at risk. Also, make sure to keep your tester in tip top shape--keep up with the latest firmware, service your tester as needed, and make sure your permanent link adapters are not worn out.

Despite all efforts, marginal passes will happen--especially if the link contains a consolidation point that adds another connection. Some customers may refuse to accept a marginal pass, wondering what happened to their supposed "premium" cabling system. This is when you want to make sure you're covered. Remember what the standards say. Unless it was specified and agreed upon in writing that marginal test results are not acceptable, your marginal passes still pass. Agreeing upon marginal test results upfront is a smart move.

Know Your Parameters

When it comes to copper certification, it's not just the margins that have changed. With the introduction of category 6A and a better understanding of applications, data transmission and what impacts performance, we now have new parameters specified as a minimum in field testing. For example, when it comes to certifying a category 6A copper system for 10GBASE-T operation, Alien Crosstalk testing is required.

There are also other newer parameters that if not passed, can cause an application to have issues.
Mode conversion parameters like Transverse Conversion Loss (TCL) and Equal Level Transverse Conversion Transfer Loss (ELTCTL) are used to measure the common mode signal within a pair, indicating proper balance for high frequency or noisy environments. And we now have DC resistance unbalance (discussed in our last blog), which can distort Ethernet signals in a PoE connection.

What you don't want is the time and expense involved in going back and retesting for parameters you didn't test for the first time. Make sure you know which parameters are required and specify them upfront so your technicians are prepared. And make sure your tester has the capability to test for every parameter specified, especially the newer ones like TCL, ELTCTL and DC resistance unbalance--which by the way, can all be tested with the DSX 5000 CableAnalyzer™.