CABLING
31
By Mark Mullins, Marketing
Manager & Founding Member,
Fluke Networks
www.flukenetworks.com
A close look at identifying a range
of different types of cable failures
alongside how and why they occur
While the most common causes of failures in twisted pair
cabling include installation errors, defects found in poor-
quality components (cables, connectors and patch cords
etc.), damage to the installed cable and incorrect tester set-
up, sometimes technicians want to know specifically WHY
a link failed. Based on which performance parameter failed
testing, there are specific possible causes that a technician
can consider. Let’s take a closer look.
Failures of the five wiremap tests
When it comes to wiremap testing that lets you know that
you have continuity and that each conductor of a four-pair
cable is connected correctly to the corresponding pin at the
far end, there are five specific tests performed: open, short,
reversed pair, crossed pair and split pair. And each one of
these has potential causes to consider.
If wiremap testing results in an open, the conductors may
be broken at a connection point, connected to the wrong
pins at the far end or not properly punched down to make
contact within the IDC tower. There’s also the possibility of
a break in the cable or a damaged connector. A short can
also indicate improper termination or a damaged connector
or cable, but it could also indicate conductive material stuck
between pins at a connection point.
Other wiremap tests are easier to pinpoint the specific
cause. In reversed pair, crossed pair and split pair results, the
cause is almost always conductors connected to the wrong
pins at the far end. A crossed pair result can also be caused
by mixing 568A and 568B wiring or the use of crossover
cables.
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