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CompTIA A+ Certification All-in-One Exam Guide

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Figure 18-12 RJ-45 pin numbers

Plenum Versus PVC Cabling

CablingMost workplace installations of network cable go up above the

ceiling and then drop down through the walls to present a nice port in the

wall. The space in the ceil-ing, under the floors, and in the walls through

which cable runs is called the plenum space. The potential problem with

this cabling running through the plenum space is that the protective

sheathing for networking cables, called the jacket, is made from plastic,

and if you get any plastic hot enough, it creates smoke and noxious fumes.

Standard network cables usually use PVC (polyvinyl chloride) for the

jacket, but PVC produces noxious fumes when burned. Fumes from cables

burning in the ple-num space can quickly spread throughout the building,

so you want to use a more fire-retardant cable in the plenum space.

Plenum-grade cable is simply network cabling with a fire-retardant jacket

and is required for cables that go in the plenum space. Plenum-grade cable

costs about three to five times more than PVC, but you should use it

whenever you install cable in a plenum space.

ANSI/TIA has two standards for connecting the RJ-45 connector to the

UTP cable: T568A and T568B. Both are acceptable. You do not have to

follow any standard as long as you use the same pairings on each end of the

cable; however, you will make your life simpler if you choose a standard.

Make sure that all of your cabling uses the same standard and you will save a

great deal of work in the end. Most importantly, keep records!

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