Stranded vs. solid cable--revisited

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.

Sep 1st, 1997

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.

Kent Merideth

Anderson University

Anderson, IN

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: ballast@utexas.edu.

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