What the #@& is Cable Certification?

What the #@& is Cable Certification?

Fluke And CableWe often use the term “certification testing” when referring to cable used in audio networks. But if a person didn’t know better, they’d think we were talking about guys in white lab coats running around with clipboards.

Hardly.

This is just another way of saying that you should test your cables to make sure they’re within manufacturer spec. Unlike the BNC and XLR world, Ethernet cable actually comes specified by The Telecommunications Industry Association (TIA) and the Electronic Industries Association (EIA) according to a “category,” as measured every 100 meters (328 feet). The current standard is the TIA/EIA-568.

You can certify that Ethernet cable is within spec using a cable test meter. Generally, you will be testing for crosstalk, egress (signal emission), ingress (picking up signals from somewhere else), and most critically, impedance.

“I always like to read the impedance first because this tells me a whole pile of stuff in one ‘go’ since it’s a combination of three other factors: resistance, capacitance and inductance,” says Steve Lampen, who’s the industry’s go-to cable guy and the Multimedia Technology Manager with Belden, which makes 6,000-plus different cables.

Unfortunately, he adds, “This is a tough one to measure, which is why you can spend up to $10,000 for a handheld meter.”

A good cable test meter will tell you if your installed cables pass or fail the TIA/EIA-568 category standards for attenuation, return loss, crosstalk, and related ratios, but not all of them will tell you why. Cable analyzers and certification meters start at $59, which will tell you if the eight wires are in the right holes and connected correctly, and run up to $10,000. The more expensive meters are able to measure the performance details for troubleshooting purposes. Steve likes the Fluke DTX-1800 (pictured), which is priced at the high end and has a data resolution of 10 gigabits. (Newer 40 gig-resolution models are expected out soon, and if you happen to get your hands on one of these, Steve would like to know).

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You don’t necessarily have to buy a $10,000 meter to certify if your cables meet specifications. Often, for a large network installation, you can buy pre-made, pre-tested cables from a manufacturer like Belden. Just provide a schematic or CAD drawing of your proposed network. Since they test and measure and certify everything, you just plug-and-play.

You can also rent an expensive test meter if you don’t want to take a chunk out of your budget for one. Generally, any electronics store will have them for rent or know where you can get one for rent. Wheatstone field engineers do their share of testing and troubleshooting cabling while commissioning WheatNet-IP networks, so be sure to ask our guys about certification testing as well.

Watch for Wires

When testing cable, Steve looks for impedance within the specified tolerance of the particular category of cable in use. The TIA/EIA standard for Cat 5e and Cat6 is 100 ohms ± 15 ohms, which is “like a barn door,” according to Steve. Specs improve with technology upgrades, for example if the wires are bonded together and whether or not it has “Zo-fit,” which is a method for managing impedance fluctuations in the cable.

If the impedance is out of tolerance, Steve suspects a problem with cable flexing or termination during installation. “I always look at the connectors and the wires going into the connectors, and it’s usually pretty obvious if they spread those wires out,” says Steve, who will test every cable in the network, from both ends.

The more space between the wires in each pair, the worse the impedance, he says. “As you go up in category from Cat 5e and Cat6 to Cat 6a, wire spacing becomes more critical because you are working at higher and higher frequencies, and shorter and shorter wavelengths, and those problems become more prevalent,” he points out. Bad impedance tolerance shows up as “return loss” where a signal can reflect back on the cable, making it harder to decode the data and reducing the effective distance.

Another common problem Steve sees in the field is a mismatch of category cable with a different category connector. “If you pick a category, everything better be that category or better than that category. If you put a Cat 5e connector on a Cat6 cable, you’ll get Cat 5e performance,” he explains.

The Skinny on Cats

When it comes to cable categories, Steve recommends you get the best cable you can afford. For any network, including an audio network, there are three categories available: Cat 5e, Cat6 and Cat 6a.

Cat6 is generally recommended for new installations because it is significantly higher performance than Cat 5e and doesn’t cost much more. Cat6 works at much higher frequencies (250 MHz) than Cat 5e, with better specs, for example, which is helpful for the kind of QoS (quality of service) you’ll get with a Gigabit Ethernet network like our WheatNet-IP. Cat 6a cable is the best performing cable (500 MHz) and it has been augmented, hence the letter “a.” Cat 6a cable has been augmented with better “alien crosstalk” capability, for example, so you’re less likely to deal with signal interference of cables in close proximity. And while Cat6 cable is better than Cat 5e cable in that it combines tight pair twists with extra insulation to reduce crosstalk, Cat 6a takes this up a notch by additionally twisting each pair around a flexible (and also twisted) central plastic support. What does all that mean, besides reduced crosstalk and better signal propagation? “On a 10 gig cable at broadcast audio quality in digital audio – 48 kHz – you can do 3,000 channels of audio down a Cat 6a cable,” explains Steve. Or, more to the point: “You have so many lanes on the highway, you would never have a traffic jam.”

For now, Cat 6a is the top dog when it comes to audio networks, but forthcoming is Cat 8 cable (40 gigabits), expected to be out sometime in 2015. Steve doesn’t recommend you wait around for Cat 8, however, because this new cable category will only go about 30 meters (100 feet), which can be a limiting factor for a lot of studio installations.

In addition to category, another cable consideration is how well these cables handle fire. The key is that the cable should not be fuel for the fire. The highest rating, and most expensive, is Plenum fire rating. Much cheaper and one notch down in fire rating is Riser. The majority of cables installed are Riser rated. Which cable to use in your installation will be decided by your designer, architect, Fire Marshal or other AHJ (authority having jurisdiction).

And, finally, don’t rule out Ethernet cable for your analog gear. “In the process of making these cables highly precise for data what we’ve done, in fact, is ended up making the best twisted-pair ever made, which is ideal for analog too, ” says Steve.

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