This is the first article in a three part series dealing with cabling materials and their role in the performance of horizontal copper data communications cable. The purpose of the series is to help cabling professionals and end users become more knowledgeable on the basics of how properties of insulating materials affect transmission, installation and network design.
As cable choices proliferate, offering a wide range
of performance, a fundamental understanding of simple principles will help the reader select and install cabling that gives the highest value for the communications dollar.
The first article in this series deals with pair insulation materials. It will be followed by an article on jacketing materials and finally we will describe how these work together in cable to enable well designed, high value cable plants.
How Insulating Material Affects Transmission
In his prophetic book Future Shock, Alvin Toffler describes what happens to people when confronted with too much change and too many choices. Nowhere is change, choice, and the pace of new developments more pervasive than in the communications cabling industry. What had traditionally evolved over years , now takes place in a matter of months or less. It seems that time has been compressed.
In just the past 12 months or so, major new developments have already profoundly affected our industry. Some of these developments are as follows:
New ANSI / TIA / EIA 568 A standards
New electronics, including networking applications which dramatically increase the bandwidth of copper.
The almost universal adoption of Category 5 cable for data communications.
New "beyond" Category 5 cables and systems offering frequencies to 350 MHz and transmission rates of 622 Mbps over 4 pair UTP.
New insulation compounds and cable constructions intended to fill the gap during the FEP shortage.
The list goes on and on. The pace accelerates. We have more choices; more information (sometimes known as hype) to sort through, more options rolling out each day and less and less time to react. Sound familiar? Like I said before, time compression.
As a minimum, how do we cope? As a goal, how do we take advantage of a fast changing industry? How do we use our knowledge and professional training to provide more value to our customers and distinguish ourselves from the competition? In short, how do we stay focused during the confusion?
Technology that affects cabling is advancing rapidly in so many areas that we have to climb multiple learning curves. We need a road map. The following three principles will help us navigate:
· Mindset · Materials · Managing
Cabling is a valuable asset and the foundation for a reliable, flexible network. Many end users already recognize that the "The Information Highway begins in Wireville."
Our experience shows that the best cabling solutions are non-prescriptive in nature and take full advantage of the capabilities of high performance insulation materials. Following standards alone, can sometimes be confining and does not always lead to the best value for end users. For example, no one should argue with Category 5 standards. They are needed, useful, and effective guidelines. But understanding and flexible thinking are even more essential. It helps to approach design and installation projects with the following mindset:
Cabling is an investment. The cable and its insulating materials have to perform without change over the life of the asset (10 to 15 years).
Category 5 standards represent a threshold level of performance required for high speed data communications.
Not all Category 5 cable is the same. Materials make the difference. Therefore there is a range of performance and range of value.
Design options and responsibility should not be abdicated to a set of rules only... even 568A. There is plenty of value stored beyond the 568A minimums. Use the standards as a baseline from which to develop the tailored solutions your customers want and are willing to pay for once they understand the benefits.
Insulating materials are a major part of the cabling asset and at the heart of the cabling investment. They are a necessary element in the equation that determines transmission capabilities, network reliability and the flexibility to accommodate new technologies.
Insulation applied directly over copper conductors is often called the primary (pair) insulation, since it determines most of the transmission properties of individual cable pairs within the cable sheath. The sheath insulation, commonly called the jacket, offers mainly mechanical protection however, it does affect the electrical performance of the cable.
Many technologies are combined to produce a high performance data cables. Variables such as conductor wire gauge, insulation thickness, concentricity, and rate of twist are critical to cable performance. However, if we assume that cable manufacturers have optimized these variables, then pair performance, such as transmission characteristics, will be further determined solely by the electrical properties of the insulation material.
Pure polymers, sometimes called resins, are the insulation materials of choice for data communications cables. Polymers can be thought of as molecular chains consisting of repeating units which are linked or bonded together through chemical reaction. Single polymers have the advantage over polymer compounds or mixtures of materials because they are chemically stable, and have uniform composition and predictable properties over the life span of the cable plant. FEP Teflon, the most commonly used primary insulation for plenum rated, high speed, high performance cable, has been exposed to the outside environment in south Florida for over 25 years with no change in physical or electrical properties.
Simply put single polymers have uniformity and longevity built in. There is less to go wrong compared to compounds or mixtures which must be fine-tuned to reach minimum requirements. New insulation compounds have been recently developed for high speed data cables, and many are finding their way into the market in response to the FEP shortage. However, recent tests on the effect of temperature and humidity indicate the possibility of degradation and loss of transmission characteristics. A recent analysis of a data cable
insulation revealed a mixture of eight different ingredients.
Of the six major electrical properties tested in accordance with ASTM test methods, two are of particular importance to low voltage data communications cable. They are dielectric constant and dissipation factor.
Dielectric constant can be described as the non-conductivity of a material relative to air, which is considered the perfect insulator having a dielectric constant value of 1.0 Since dielectric constant varies as a function of frequency and temperature, high temperatures polymers are less affected than lower melting point compounds at frequencies below 10 MHz.
It is also very important to note that time delay, or it's inverse, velocity of propagation is determined by dielectric constant. Time delay is directly proportional to the square root of the dielectric constant. The lower the dielectric performance, the less time required for a signal to travel down a given length of cable. Velocity of propagation is a vital measurement used by hand held testers to determine cable distances. Wide variations in this value can spell trouble.
Signal transmission down a length of cable occurs mainly at the copper/insulation interface. The tendency of insulation's to dissipate or absorb electrical signal energy in the form of heat is one of the causes of attenuation. As with dielectric constant, dissipation factor is also a function of frequency and temperature. Higher temperatures increase dissipation and therefore attenuation.
The following are typical values of commonly used primary insulation's for plenum data and cable. These values are for solid insulation's. Insulation foaming techniques, which encapsulate air, further reduce dielectric constant and dissipation. Of all the insulation types available for communications cable, FEP is unique. It has the lowest dielectric constant known for functional insulating materials.
Comparison of Communication Cable Insulation (Tested at 1 MHz)
In summary, the transmission performance of data cable can be directly proportional to the dielectric constant and dissipation factor of the primary insulation. The lower these two values, the greater the ability of the cable to carry data at high rates over extended distances. This will pay big dividends in network cost and design simplicity as we will see in a later article.
Managing procurement of the right cable, cable plant design and installation has become more complex. Add to that the shortage of FEP and managing becomes more like choreography.
Unfortunately, there is no magic pill. To deliver top value in a structured cabling system, complete understanding of the cable's transmission characteristics right down to the insulation materials is essential. In our approach, we analyze performance limits to determine what the cable can do. Merely meeting a minimum standard is not good enough.
As mentioned previously, new Category 5 MMP/CMP constructions have been introduced which are designed to stretch the FEP supply by using a substitute insulation for one of the four pairs. These hybrids may be an alternative to Category 5 MMP/CMP cable, but they give us cause for concern. There are still unanswered questions as to how this system performs when all four pairs carry signals to maximize bandwidth. Will differences in velocity of propagation be a problem for time sensitive transmission protocols delivering
multimedia? (One of our distributors refuses to stock these constructions because of this question.)
We buy the best cable available and insist on the same insulation for all four pairs, whenever possible. I suggest you prepare yourself to pay a higher price, because the extra value is worth it. But, best does not always mean most expensive. In a recent cable procurement for Category 5 CMP, we found little, if any, relationship between cable price, cable construction and value. One hybrid cable with three pairs insulated with FEP and the fourth a substitute material was more expensive than four pairs insulated with FEP, Go figure.
Perhaps this is a temporary condition in an ever changing market and the laws to supply and demand will eventually bring balance and order. But, I wouldn't count on it. We stay in close contact with distributors and, because of availability issues, manage one day at a time. We navigate by sticking with proven, high performance cable and materials because we know these ultimately deliver the greatest value to our customers.
About The Author
Francis (Frank) W. Peri Communications Design Corporation President
Frank Peri, a retired DuPont Marketing Manager, is the President of an independent one-man consulting firm, Communications Design Corporation, based in Kennedyville, MD. CDC specializes in marketing support, codes and standards representation for manufacturers of communications systems infrastructure and high-performance structured cabling systems for voice and data networks. Mr. Peri's work has been primarily focused on DuPont, with a goal of presenting DuPont's TeflonŽ FEP value story to the large communications end-users, facilities managers and industry groups. Mr. Peri's career includes membership in many industry organizations, including:
Member TIA (Telecommunications Industry Association) TR 42.1 Standards Committee, Commercial and Industrial Cabling Director of ACP (The Association of Cabling Professionals) Member BICSI (Building Industry Consulting Service International) Member Codes and Standards Committees and BICSI liaison to NEMA (National Electrical Manufacturers Association) and ICEA (Insulated Cable Engineers Association) Member NEMA Premises Wiring Subcommittee. Member ICEA - TWCSTAC (Telecommunications Wire and Cable Standards Technical Advisory Committee) Member NFPA (National Fire Protection Association) Technical Committee member of NFPA 90A and Building Standards Committees Mr. Peri is a contributing author to Cabling Business Magazine and other major publications. He is also a frequent seminar presenter and trainer at industry conferences.