Q: On page 44 of the April 1997 issue of Cabling Installation & Maintenance, you responded to a question concerning stranded versus solid cable attenuation. I have known since day one that stranded cable would have more attenuation than solid cable because of the "skin effect" in high-frequency transmissions. I had suspected about 10% to 15% attenuation, but had never heard any specific numbers. Your response--20%--was the first quoted number I have seen.
Could you give me a reference to any literature that I could use to show unbelievers I keep butting up against? It would really be great if it came from Lucent Technologies because one of the contractors who humors me on this subject is a Lucent vendor. I can tell that the technicians at this company just do not believe there is more attenuation in stranded cabling. After all, 24 awg is 24 awg.
A: How about citing an American National Standards Institute standard to make your case? ansi/tia/eia-568a, Clause 10.5.4.1--"utp Patch Cords and Cross-Connect Jumpers--Attenuation," allows a 20% increase in the attenuation for stranded construction. This is not to say, however, that all stranded constructions will have the maximum of 20% attenuation over solid copper. But it could, and still meet the Category 5 specification.
As for your sparring partners at the contractor and their connection with Lucent Technologies, ansi/tia/eia-568a, Chapter 10--"100-ohm Unshielded Twisted-Pair (utp) Cabling Systems," was the responsibility of the Telecommunications Industry Association`s utp Systems Task Group, chaired by Masood Shariff of Lucent Technologies` Bell Laboratories. Touché.
This becomes an issue when the length of the stranded cable exceeds the allotted 10 meters of the 100-meter channel--for example, with a work-area cable connecting to a multiuser telecommunications outlet assembly.
tia/eia TSB-75, Section 5.4--"Multi-User Telecommunications Outlet Assembly, Horizontal Distances of Copper Links," gives us a formula to determine how much we must shorten the length of horizontal cable to accommodate the extended length of the work-area cable. And, for those of us who don`t carry a scientific calculator on our tool belt, a table is also provided. Installation of a 20-meter work-area cable reduces the length of horizontal cable to 70 meters. Adding the 7 meters allotted for patch cords and equipment cable, this equals a 97-meter channel.
Donna Ballast is a communications analyst at the University of Texas
at Austin and a bicsi registered communications distribution designer (rcdd). Questions can be sent to her at Cabling Installation & Maintenance or at PO Drawer 7580, University of Texas, Austin, TX 78713; tel: (512) 471-0112, fax: (512) 471-8883, e-mail: email@example.com.