Rob Bellassi
Underwriters Laboratories Inc.
They say the world keeps moving and, if you don`t move with it, it will pass you by. In our industry today, this adage is more apt than ever before. With the recent publication of its wc66-1999 standard, the National Electrical Manufacturers Association (NEMA--Rosslyn, VA) has established transmission-performance requirements for Category 6 and 7 cable.* This new standard increases twisted-pair copper-cable transmission requirements from the current 100-megahertz bandwidth to 250 MHz for Category 6 and 750 MHz for Category 7. It also raises the technology bar and challenges third-party certifiers to find better ways to test cable performance.
Copper twisted-pair transmission-performance testing began with manufacturers performing very basic electrical tests. Through the early 1900s, testing for direct-current resistance and capacitance was sufficient because applications such as the telegraph did not require high-performance cable. But with the advent of the telephone, crosstalk also became an issue. Engineers discovered that you could decrease crosstalk by altering pair twist. Through the early 1980s, specifications were published to these basic minimum-performance requirements.
With the invention of the computer, everything changed. Standards bodies were formed and began developing standards, beginning with Category 3 performance testing to 16 MHz. Today, new standards are propelling shielded and unshielded twisted-pair transmission-performance requirements to new levels, and manufacturers and end users are striving just to keep up.
Industry demands
Today`s computers transmit data at never-before-seen speeds and perform tasks that a few years ago were unimaginable. With technology moving at a 21st century pace, network designers and IT managers want the best equipment available to perform the job. The cable in a local area network is as important as the computers and hardware connected to it. As end users, IT managers need to know that systems are functional for years to come.
For cabling installers, installing the highest-performing cable reduces business liabilities, particularly with warranty programs offering performance guarantees. To make sure the entire cabling infrastructure performs at the highest possible level for the application, use not only the highest-performing cable, but also connecting hardware that will perform at the same performance level or higher.
For cable manufacturers, it is important to test at and beyond the current requirements. Such tests give manufacturers more confidence in their own quality-assurance testing programs and enable them to produce better cable.
Certifiers must also keep up
The recent changes in cable-performance requirements also challenge third-party certifiers. In April, Underwriters Laboratories Inc. (UL) became the first third-party certifier with the capability to test copper cable to 1.2 gigahertz--450 MHz higher than the Category 7 requirement in wc66-1999.
UL tests shielded and unshielded multiconductor cables to all published and draft standards available to the telecommunications industry. Our data-transmission performance marking programs include comprehensive, repeatable testing up to 1.2 GHz, using the latest Hewlett-Packard automatic cable test-measurement system. Although it is possible to test at higher frequencies with this system, the accuracy of the data produced is limited because of calibration factors.
The test-measurement system is capable of performing more than 60 tests, including longitudinal conversion loss, longitudinal conversion transfer loss, and attenuation deviation. In addition to testing performed at UL, the program requires testing be performed at the manufacturing facility. Each manufacturing facility authorized to mark and label UL-verified cables is also subjected to an iso-9000-based quality audit performed in the UL Quality Registration Services Department or by auditors from the Wire and Cable Department.
Where will the industry go next? How high will the bar be in 10 years? That is anybody`s guess. But for now, testing cable up to 1.2 GHz is a way of being ahead of the game for many years to come.
*NEMA`s wc66-1999 standard for cable should not be confused with the tia/eia`s proposed standards for Category 6 and 7 end-to-end structured cabling systems.--Ed.