atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services Cabling Telephones Systems Wiring One place where you shouldn't use CAT5

Always on the lookout for reasons to discredit the use of CAT5 and CAT6 for anything but its intended purpose I came across this over at the Pro AV forum. It was in response to someone asking what "baluns" to use to put audio and video on 800 feet of CAT5. Besides making a point about the terminology and use of baluns Brad Weber, who is a respected authority had the following to say:

Also, in direct opposite convention from data, audio and video over UTP generally works better over CAT than CAT5e which is in turn better than CAT6. The increased and varying twist rates that are an advantage in data introduce additional skew that is detrimental in audio and video applications. You can use CAT5e or CAT6, just be aware that skew can become a larger problem.


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Brad Weber
muse Audio Video

-Hal

I thought Belden and some others make a low-skew cat6 cable for video applications.

The latest and greatest isn't always the best, and bigger isn't always better, but you can't convince some people of that. Hal will appreciate this more than most:

About two years ago we built out new offices. I did all the wiring including the electrical. I had to brush up on my code book as the city had just switched to the latest code. The electrical inspector (who has never run a wire in his life, big surprise) and I were discussing the fact that 14 ga. was no longer allowed. He chimed in and said that he was pushing for 12 guage to be banned as well and move everything to at least 10 guage or better.

Hal can you imagine working a 6 gang switch box with all #10? :bang:

There are some locations in the country that prohibit 15 amp/14ga circuits in a commercial installation. Even where not prohibited the norm is to install no smaller than 20 amp circuits which require 12ga wire.

You might not know the real reason behind this which has to do with fault current and circuit breaker interrupting capacity. In many commercial and industrial locations the electrical service to the building is capable of supplying a much higher instantaneous current during a short circuit than most residential areas. It is possible for smaller 14ga wire to be damaged from something like a dead short even before the breaker has a chance to open. The thinking is then that with 12ga and larger this is less of a problem.

So, apparently your inspector doesn't know the theory behind using 12ga wire or he wouldn't be making such dumb statements.

-Hal

That is an accurate statement. For AV, only CAT-5 should be used due to the twist rates.

This has been known for quite some time and is one of the few reasons that CAT-5 is still manufactured. Especially since the latest EIA/TIA-568 standard removed CAT-5 from being an authorized medium for structured cabling systems.

I should point out I believe "CAT" in his first sentenance is a typo, should be CAT5. Brad is saying that old CAT5 is preferred over CAT5e and CAT6.

-Hal

Thanks, good to know. I knew there was a reason I was using up all the old stock Cat5 for audio/video only!

The move from Cat5 to Cat5e for structured cabling has meant that buying Cat5 has become near impossible. Every school in Northern Ireland has been rewired within the past five years using Cat5e, and the structured wiring systems are used for just about everything - computers, telephones, video etc.
The key to using Cat5e effectively is to use good equipment! Substituting a cheap KVM switch for a "real" UXGA extender will no doubt show up the skew problems! Many "pro" manufacturers now include skew compensation in their products, or manufacture add-on skew correctors. I've seen these in action, and their claimed bandwidths of 350MHz over 300ft do seem to live up to the manufacturers claims.
Yes, the equipment to push audio and video down Cat5e is expensive, though it is getting cheaper. It also means that jobs which could not otherwise be done, can be. (For example, one of our Education Board's has an outside broadcast vehicle which visits schools. Using the structured cabling, they can get video signals to and from anywhere in the school, without laying dangerous temporary cables, or having to have permanent video cables installed).