Check for wires that were not fully seated in the crimping process. Also
check to see if the correct type of RJ-45 was used, stranded or solid wire
pins. This is difficult once the end has been crimped. Using the wrong style of
pin may cause intermittent connections after a period of time, though the cable
usually works immediately after it is made.
If a non-proprietary
terminator with a non-standard pinning is used, the connection may look the
same but the internal wiring could be off.
Check on the standard used.
There have been notable cases where large campus sites have been wired by two
different groups of contractors. If the cabling process is not coordinated
correctly different contractors may use different wiring standards in their
cabling. This would result in incompatible wiring schemes in the two halves of
what was meant to be a single network.
Cabling length is also a major
issue. Cabling guidelines are constructed to take into account factors such as
propagation delay and signal attenuation, which are related to the length of
the cable used.
Other issues such as grounding and ability to exclude
internal and external noise from interfering with data transmission must also
be taken into account. UTP is not the correct cable type to be laid near strong
sources of external EMI. Either shielded CAT5 or optic fiber must be considered
as a replacement.
More dangerous is where there is a different
electrical potential at each end of cabling runs. The terminating device may
become live and capable of discharging significant voltage to other attached
equipment. In this case, fiber-optic cable is to be used instead of UTP or STP,
because it does not carry an electronic signal.
