Q: In the May 2000 issue, an article in the Industry Spotlight (see "Category 3 minimum FCC-approved for all new copper-cabling installations," page 119) discussed Federal Communications Commission (FCC) requirements concerning all new twisted-pair cabling installations. My questions: Is it an FCC requirement to install Category 3 or better for telephone and data? Can the Category 3 be 2-pair, or must it be 4-pair? Is RG6U (75-ohm coaxial cable) also required for cable TV? Also, where can I get a copy of the FCC requirements?
Jim Holshouser
Electrical Inspector
via e-mail
A: On January 10, Title 47 of the Code of Federal Regulations, Part 68-Connection of Terminal Equipment to the Telephone Network, Section 68.213, was amended to require Category 3 or better cable.
Specifically, paragraph (c), Material Requirements, now reads: "The Federal Communications Commission has established minimum telephone inside wiring quality standards to promote consumer access to existing and advanced telecommunications services. Our definition of telephone inside wiring refers to wiring located on the customer premises side of the telephone network
"1) For new installations and modifications to existing installations, copper conductors shall be, at a minimum, solid, 24-gauge or larger, twisted-pairs that comply with the electrical specifications for Category 3, as defined in the ANSI/TIA/EIA Building Wiring Standards.
"2) Conductors shall have insulation with a 1,500 Volt RMS minimum breakdown rating. This rating shall be established by covering the jacket or sheath with at least 15 cm (6 inches) (measured linearly on the cable) of conductive foil, and establishing a potential difference between the foil and all of the individual conductors connected together, such potential difference gradually increased over a 30-second time period to 1,500 Volts RMS, 60 Hertz, then applied continuously for one minute. At no time during this 90- second time interval shall the current between these points exceed 10 milliamperes peak.
"3) All wire and connectors meeting the requirements set forth in subparagraphs (1) and (2) above shall be marked, in a manner visible to the consumer, with the symbol "CAT 3" or a symbol consisting of a "C" with a "3" contained within the "C" character, at intervals not to exceed one foot (12 inches) along the length of the wire."
It is my personal opinion that to meet the electrical specifications for Category 3 cable in TIA-568A, the cable must be a 4-pair cable or a multipair (greater than 4-pair). However, I have followed the FCC proceedings on this issue over the years and do not believe this was the intent of the commissioners when they approved these minimum requirements. Hence, this issue is open for interpretation by the authority having jurisdiction. From where I sit, that places it squarely on the electrical inspector's plate, which I assume is why you are asking in the first place.
There was no mention of the FCC establishing minimum standards for inside-wiring quality for cable-TV cabling.
As for the FCC's rules, the commission currently has all of its rules and regulations online at www.fcc.gov/. You may also want to search the Code of Federal Regulations at www.fcc.gov/oet/info/rules/crf.html; Federal Register at www.access.gpo.gov/su_docs/aces/aces140.html; or Title 47 of the U.S. Code at www4.law.cornell.edu/uscode/47 for additional information.
Multimode or singlemode for Gigabit Ethernet
Q: I want to begin with a quick word of appreciation. Your answers to questions in this publication are always standards-based and very helpful to many. I do want to comment briefly on a recommendation made recently in the June 2000 issue, in which you (or actually the Institute of Electrical and Electronics Engineers-IEEE) make the recommendation for 62.5/125-micron fiber in the backbone for distances up to 100 meters, and 50/125-micron fiber for distances greater than 100 meters and less than 300 meters (see "Ask Donna," page 8). We have found here at Central Washington University that this solution, although standards-based and useful, makes it quite difficult to administer the cable plant. The probability of installing a 62.5/125-micron fiber jumper in these links is likely, and as I'm sure you know, the resulting core mismatch will create many troubleshooting sessions.
Our strategy in this situation has been to place both singlemode and multimode fiber in the building riser system. Gigabit-speed electronics have come down pretty drastically lately, and the costs of fiber installs are not what they used to be, with the advent of labor-saving connectors and such. This also provides a great medium for other applications beyond Ethernet. One small word of advice, however: The person who defines the connector specifications should be aware of characteristics such as reflectance values. There are some "no-polish" connectors on the market today with reflectance values very close to the values that historically have been seen only in angle-polish connectors-an expensive option that I believe should be avoided when possible because of the high cost of the equipment needed to repair damaged connectors.
Patrick Shannon, RCDD
Central Washington University
Ellensburg, WA
A: I personally agree with your choice to install both 62.5/125-micron multimode and singlemode fiber in the building backbone. The multimode fiber provides excellent legacy capability and Gigabit Ethernet performance. The singlemode fiber will provide for 10-Gigabit Ethernet and beyond.
Only one word of caution: administration. Unless you are using different connector types for different types of fiber, you can easily plug a 62.5/125-micron multimode fiber patch cable into a singlemode link as well. There is no substitute for good cable administration.
While 50/125-micron multimode has been used in Germany, the United Kingdom, and Japan, North America has primarily used 62.5/125-micron multimode. Currently, I cannot see any reason to add another fiber type to the mix. But we may all want to revisit this idea once the dust settles on the "next-generation" multimode fiber.
"Next-generation" multimode fiber is a product concept based on an 850-nm-optimized 50-micron fiber and will support 10-Gigabit Ethernet transmission over a minimum of 300 meters. The concept has been presented jointly to various standards bodies by Corning (Corning, NY) and Lucent Technologies (Murray Hill, NJ). This fiber type would use vertical-cavity surface- emitting lasers (VCSELs) to support 10-Gigabit Ethernet, rather than the lasers required for singlemode fiber. VCSELs cost less than other lasers, but I would not think that the cost of one component in the network equipment could possibly offset the cost different between singlemode and "next-generation" multimode fiber.
And then there is the nagging question of, "What's next, 100-Gigabit Ethernet?" The IEEE has scheduled the 10-Gigabit Ethernet standard for completion in March 2002 and should provide fiber specifications by November. Until then, it's anyone's guess. But singlemode will definitely be on the list.
Shielding telephone-riser cable
Q: A point of discussion here concerns voice riser cable. Is there a compelling reason to use shielded instead of unshielded cable for the voice riser? With the unavailability of plenum-rated shielded cable, this issue is a real sore spot in the overall design of riser systems. Can you give us some input, or guide us to any significant studies on the subject?
Gordon Graham
State of Utah
via e-mail
A: I am certain that you, as a state employee, have heard more than once, "That is the way we do it here, because that is the way we have always done it." But this one goes back to the days before Ma Bell met Judge Greene.
The purpose of "shielding the riser cable" is to equalize any voltage differential that arises during transient conditions. There are basic forms of coupled bonding conductors: a cable shield or a separate conductor (typically 10 AWG) fastened (usually with cable ties) to an unshielded cable at regular intervals. To work properly, the coupled bonding conductor must be connected to ground at each end of the cable.
Donna Ballast is a communications analyst at the University of Texas at Austin and a bicsi reg-istered communications distribution designer (rcdd). Questions can be sent to her at Cabling Installation & Maintenance or at PO Drawer 7580, the University of Texas, Austin, TX 78713; tel: (512) 471-0112, fax: (512) 471-8883, e-mail: [email protected].