Reference Guide
Crestron
CAT5 Wiring
Electrical Measurements of CAT5E Wiring
The specifications for CAT5E wiring can vary within a range as specified by
TIA/EIA. These specifications depend on the kind of connections (permanent,
patchcords, etc.), the length of cable run, and the type of termination connectors. The
following are a list of measurements that are made on CAT5E cables.
•
Attenuation
is a measure of signal loss from one end of a cable to the
other, and is measured in each pair of wires.
•
NEXT
(Near End Cross Talk) is a measurement of noise that is coupled
from an adjacent pair of wires, usually the receiving pair and the
transmitting pair. NEXT is measured for all pair combinations.
•
PSNEXT
(Power Sum NEXT) is the measurement of one pair while all the
other pairs are in use. This calculation is made for each pair in the cable.
•
Delay Skew
(Propagation Delay) is the measurement of signal speed
through the wires. All the wires of the cable are fed the same signal
simultaneously. The time difference at the receiving end of each wire is
measured, and the shortest time is subtracted from the longest time.
•
FEXT
(Far End Cross Talk) is measured by transmitting on one pair and
measuring cross talk on an adjacent pair at the far end of the cable.
•
ELFEXT
(Equal Level Far End Cross Talk) is FEXT minus Attenuation.
•
PSELFEXT
(Power Sum ELFEXT) uses all wires in the cable.
•
ACR
(Attenuation to Cross Talk Ratio) is a measurement of the ratio of
signal to noise and reveals the bandwidth of the cable. It is derived by the
difference between NEXT and Attenuation.
Installation Notes
•
Never pull CAT5 wire with excessive force. The CAT5 tension limitation is
25 lbs, much lower than standard audio/video cable.
•
Never step on or crush, kink, or crimp CAT5.
•
Avoid periodic sags; vary the intervals if the cable must sag.
•
Do not bend CAT5 wire tightly around a corner; ensure that it bends
gradually, so that a whole circle would be at least two inches in diameter.
•
Do not allow knots or kinks, even temporarily.
•
When using conduit, do not fill to more than 40% if using more than two
cables (National Electrical Code, Chapter 9, Table 1).
•
Never untwist the two wires in a single pair for more than 1/3-1/2"
(0.84 – 1.27 cm) when making a connection (the twists are critical to
canceling out interference between the wires).
•
Never run CAT5 parallel to power wiring closer than six inches.
•
Avoid splices. Every splice degrades the line.
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Crestron CAT5 Wiring
Reference Guide - DOC. 6137A