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CABLING
"Non-standard cables like CCA cannot legally be
installed to meet National Electric Code fire
safety ratings, resulting in code violations and
increased risk of fire"
Length failures beyond the obvious
While one might think that exceeding length limits obviously
means that the cable is too long, that’s not the only
potential cause. Another cause could be that the NVP is
set incorrectly. NVP, which stands for nominal velocity of
propagation, characterises how fast a signal is travelling
down the cable relative to the speed of light in a vacuum,
and it’s what allows the tester to calculate the length of the
cable. Expressed as a percentage, NVP is set using the NVP
specification provided by the cable manufacturer. And if it’s
not set correctly for the cable under test, you might exceed
length limits.
When length reported is shorter than the known length,
it could indicate a break in the cable. And if one or more
pairs are significantly shorter than the others, there could be
cable damage or a bad connection.
Causes of the losses
For return loss failures, there are several causes to consider,
most of which can be attributed to poor installation practices.
Patch cords could have been mishandled causing changes
in impedance, cables could be kinked, or pairs untwisted.
It’s possible, however, that patch cord or cable impedance is
wrong (it should be 100 ohms) or not uniform. Bad connectors
or poorly matched plugs and jacks can also cause return
loss failures. And don’t rule out testing issues – you need to
make sure the correct autotest is selected and that your link
adapters are working. And if you have an unexpected return
loss PASS, remember that knots and kinks don’t always cause
a failure, especially when using good quality cable.
Insertion loss, the loss of signal that happens along the
length of any cable, can be a little easier to pinpoint. Since
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