Video

Tie Wraps & Cables Don’t Always Mix

cable-ties

Checklist Item Under Test: 6.1.10: CatX or twisted pair cables and coaxial cables have hook and loop fasteners, and there are no cable deformities caused by poor dress or fasteners being too tight.

Reasoning: As AV professionals, we spend good money on high-quality cable. We expect it to perform to its specifications. With data rates continuing to climb, cable integrity becomes all the more important. If category cabling or coax cabling is compressed in any way, either from tight bends or overly tightened tie wraps, it will no longer provide the transmission properties we require. Cables must be neatly and gently dressed to maintain the signal integrity in our systems.

The Story: When I first got into AV, one of my favorite tools was the tie wrap gun. I may or may not have made a holster for it. I may or may not have called myself “Jimmy the Kid” and swaggered up to the equipment rack I was about to duel with. I may or may not have blown invisible smoke away from the business end of the gun after each “shot.” The cable ties never had a chance. They would be neatly trimmed with every trigger pull. They feared me. It was glorious.

As much as I loved the tie wrap gun, I did not respect it. I enjoyed using it, but I never took the time to appreciate all its nuances and subtleties. Some of my cuts caused cable bundles to be pinched, but I thought it looked cool and showed off what a tight, neat cable bundle I made. What I’m trying to say is, I just didn’t know the wheel at the base of the handle was a tension adjuster. I never noticed it. And from the look of many installs we commission, a lot of installers don’t notice it either.

I’m sure we are all familiar with overzealous cable tie pullers. I’ve seen installations where the tie wraps were so tight they had cut into the cable jackets. The scars on my fingers and forearms remind me of why tie wrap guns and their smooth cuts are alluring. I’m sure some installers were working out some aggressions, as well, by cranking down on the cable ties…but it is important to understand why this is a problem, especially with coax and category cables.

The coaxial cable gets its name from the center conductor and shield, typically layers of woven metallic braid, sharing an axis. Both are considered “co-axial,” and much of the cable assembly’s resilience against electric and magnetic fields stems from this shared axis construction. In today’s systems, coaxial cable is typically carrying very weak signals (wireless microphone RF) or very high-bandwidth signals (3G-SDI). It needs as much help as possible to get these signals from source to destination. Any cable deformation that the cable suffers will alter its coaxial nature and reduce its performance somewhat. In a congested RF space or busy video installation, this could be disastrous.

Category cables can carry 10GB of data! On copper! With the introduction of higher twist ratios and better crosstalk separation between the twisted pairs, the bandwidth capacity has increased over the years. With the need for 4K resolution transmissions, it couldn’t come soon enough. I’m sure you’ve seen the finicky nature of some of these cables in the field. HDBaseT transmitters and receivers might work perfectly with certified patch cables in the shop, but once you get into the field, you run into issues. Many are termination problems, but many are cable run/installation issues.

The specification of the Valens chip many of these converters use only permits six cables for a 30m run because of alien crosstalk issues. With all of the 16×16 or 64×64 matrix switchers being sold, I’m not sure this specification is being followed. So, deforming the cables with tight cable ties only exacerbates the crosstalk issue. Not only will this deform the carefully determined twist ratios of the pairs, but it will squash the pairs in the bundle together, increasing crosstalk internally and externally to the cables.

We are pushing copper data rates to their limits. We need to treat the cables with respect. Velcro ties are a fantastic solution. They are wide, soft and cannot be tightened excessively. Plus, they are easy to reuse. If you have to use cable ties, do not overtighten them. Make sure the cables in the bundle can move easily, and for the love of all that is holy, make sure the cable jackets are not pinched or deformed in any way. That still leaves the issue of cutting the tail off the tie wrap, and “Jimmy the Kid” is yearning to break out ol’ Betsy (that was her name: my sweet, sweet tie wrap gun). However, there are several inexpensive diagonal cutting shears on the market that do a great job of cutting the tie wrap safely and without destroying the integrity of the cable. I’ll admit, the holsters aren’t as impressive, but at least your data can mosey on down to its destination safely-like.

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