In Part I of this series, I discussed the basics of low-voltage copper cabling for voice and data. Now I want to go into more detail about UTP, how it is categorized, certified and rated.

In Part III, we will go into optical fiber for communications cabling and in Part IV I will discuss Structured Cabling Systems for voice and data.

The Way It Used to Be

UTP, of course, comes in a variety of flavors and I will try to discuss the major ones here. Back in the bad old days, UTP was UTP. Whether it was a 50- or 100-pair cable or the “silver satin” cable used for telephone line cords, you might know what gauge the wire was, but you didn’t really know what the performance characteristics were.  All of this changed in the 1990s when a group called EIA/TIA (Electronic Industries Alliance and Telecommunications Industry Association) created a set of categories to begin to differentiate between the performance characteristics of various kinds of UTP.

I’ll Take Categories for $200, Alex

In 1995, EIA/TIA came up with three main types of cables: Category 3, Category 4 and Category 5. Pretty imaginative naming, huh? Category 3 was suitable for voice and for data rates up to 10 Million bits per second (Mbps). Category 4 cable was for data applications between 10 and 16 Mbps  (Quick Quiz: Do you know why that odd upper limit was used? Answer in the comments!)  and Category 5 cable was to be used for applications above 16 Mbps up to 100 Mbps. They really didn’t anticipate data rates going beyond that limit, or at least cable technology was not able to support higher data rates at that time. All of these cables are 4-pair UTP, 24 Gauge. All 4 pairs must be terminated on both ends to provide the performance specified for the category. More on termination later.

A short time later, they came out with the Category 5e (the ‘e’ for ‘extended’) specification, allowing data rates up to 1000 Mbps (1Gbps=1 Gigabit per second) . The advent of Category 5e cable rendered Category 4 and Category 5 cable essentially obsolete. Throughout the ’90s and much of the early 2000’s, Category 3 was commonly used for voice cable and Category 5e was commonly used for data cable.

In 2008, this specification was extended to include Category 6. Just as they did with Category 5, TIA (they had dropped the EIA from their name by now) very quickly issued a revised spec for Category 6A (augmented) which essentially rendered Category 6 obsolete. Category 6A cables can support data rates up to 10 Gbps over the same length run as the previous categories (100 meters or about 300 feet).

I’m Certifiable!

The other innovation introduced with the cable categories was the concept of certifying cable. A cable tester is used to certify the installed cable to meet the performance characteristics of the specification. So, when you have a Category 6A cable run installed and certified, you can feel confident that your 10 Gbps data hardware will run fine over that wire. Certification is a tremendous benefit for cable consumers and it has really helped eliminate some of the shadier cable providers.

Categories extend beyond just specifying the cable; they also included the connecting hardware. So there are Category3 jacks and Category 6 patch panels, patch cables, etc. Cables are typically terminated on either terminal blocks or patch panels in the telecom closet and on a jack out at the station end. In order to end up with a certified cable run, the cable type must match that of all connecting hardware, end-to-end. So, don’t think you can improve Category 3 cable by terminating it on Category 5 patch panels. It doesn’t work like that!

Since the cable is 4-pair UTP, the jacks used must support 8 wires. The jack used is called a RJ-45. There used to be two differing standards for terminating the jacks: 568-A and 568-B. Today, thankfully, 568-B is deprecated and most termination for new installations is done to the  568-A standard as shown.

 Don’t Forget Your Jacket!

The final subject I want to cover in this post is that of the cable jacket. The cable jacket is the plastic coating of insulation around each individual strand of wire and around the 4-Pair cable itself.  Any of the above discussed cables will generally be available in either of two jacket types: CMP and CMR. Cable with a CMP rated jacket is known as Plenum-Rated cable. Cable with a CMR rated jacket  is often referred to as Non-Plenum Rated or Riser Rated.  CMP is used in many office environments where the return air for HVAC routes through the ceiling (plenum) space. In the event of a fire, CMP cable jacket emits much fewer toxins, so poisonous fumes are not spread throughout the facility as the smoke gets sucked in by the HVAC system. Where return air is not routed through the ceiling, CMR cable can be used. Consult your building engineer for the correct cable for your application. This is a very important distinction.

My next post in this series will cover optical fiber.

Do you know why Category 4 cable was specified to 16 Mbps? What other copper-related tips can we pass on to cabling newbies? Share your thoughts in the comments.

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