Cable And Crimping Quality; The Importance Of A Proper Crimp; Type Of Wire - Lighting Controls Blue Box LT Series Installation, Operation & Maintenance Manual

THE BLUE BOX LT MAKING UP CAT. 5 CABLE WITH RJ45 CONNECTORS 31

CABLE AND CRIMPING qUALITY

THE IMPORTANCE OF A PROPER CRIMP

Imperfections in a crimp adds a resistive and capacitive load
at that point in the network . For example, if the voltage is
dropped to 75% of its previous value at each crimp, the
signal voltage will drop from 5V to 3 . 7 5V on the first crimp
and 2 . 8 V after the second .
Therefore, multiple bad crimps can cause the signal to be
lost in the noise threshold after consecutive voltage drops;
this loss of signal through the length of a cable is called
attenuation . Impedance is the measurement of cable
resistance to a signal, measured in ohms .
If the RJ45 connectors are improperly terminated, the
additional resistance and capacitance at the connector
changes the "character" of the wire causing what is called
an impedance mismatch .
Impedance mismatch causes signal attenuation because
part of the transmitted signal is reflected back much like
an echo and does not reach the receiver . Inconsistent
crimps compound these effects and cause a larger part of
the signal to be reflected back .
When these reflected signals collide with the first
discontinuity, part of the signal will return to the original
direction and create multiple echo effects . This results in
an "unstable bus" because these reflections or echoes
make it difficult for our devices to receive data .
Figure 1 . 4 shows a daisy-chained network; if there are bad
crimps as described above the transmitted signal from the
relay panel can lose strength with every device .

TYPE OF WIRE

There are three types of wire that use RJ45 crimped
connectors . The first is a flat telephone cable, made of 26
gauge wires . It is not Cat . 5 since the wires all run parallel to
each other and are not twisted and thus lack immunity to
noise . We use this type cable for low frequency signals and
short distances, such as to provide power to the clock .
The other two cables are round in form . They come in
stranded and solid varieties . The stranded wires are used
for "patch cables" from a computer to a wall socket .
Figure 1.4