Q: It has been suggested that we use shielded twisted-pair (stp) cable for vertical runs at my company, since some runs might exceed the 90-meter maximum of unshielded twisted-pair (utp) cable. Does stp allow longer runs, or are the specifications the same?
Jim Vizzaccaro
Source One Mortgage Service Co.
Farmington Hills, MI
A: The length specifications are the same. The tia/eia-568a Commercial Building Telecommunications Cabling Standard of the Telecommunications Industry Association and the Electronic Industries Alliance (tia/eia--Arlington, VA), in Section 5.5--Backbone Cabling Distances, states: "The use of Category 5 multipair utp backbone cabling for applications whose spectral bandwidth is in the range of 20 to 100 megahertz should be limited to a total distance of 90 meters (295 feet)." It also states: "The use of 150-ohm stp-a backbone cabling for applications whose spectral bandwidth is in the range of 20 to 300 MHz should be limited to a total distance of 90 meters (295 feet)." Hence, stp-a would allow you to go faster, but not farther. For that, you need optical fiber; and as for which optical fiber, that also depends. Once you know the length and have some idea of applications you will be required to support, then you can select your media. The table indicates the maximum supportable distances and the maximum channel attenuation for various optical applications by fiber type