Information Technology Reference
In-Depth Information
times, a single loop twists so that it does not feed in a spiral fashion; as the loop col-
lapses, a kink results. Of course, kinks can occur easily in loose coils of cable that
have been unboxed or unreeled. Try to avoid kinks, particularly in Category 5e/6
operation. If a kink occurs, attempt to smooth out the kink as much as possible, but
be aware that you may have to replace the run if it later fails in testing.
The TIA-568-C standard recommends a minimum bend radius of four times
the cable diameter. For most cables, that radius is about 3/4 to 1 in. Try to avoid
pulling cable tightly around corners and use cable management retainers to provide
a smooth transition to the point of termination.
Connector Opens.
Modular connectors may fail because of open connections. The
most common conditions are bad plug crimps, dislodged wire, bent jack pins, and
bad connector seating. The popularity of modular plugs in telephone wiring has
resulted in the availability of low-cost, 6-pin crimp tools. These tools may be made
from plastic or lightweight steel. Unfortunately, the flimsy design has been extended
to 8-position crimpers.
The 8-pin modular plug is much more difficult to properly crimp than plugs
with 6 pins. A low-cost tool often cannot properly seat the connector contacts in the
center of the plug. This may result in one or more of the stranded wires not making
contact or, worse, making intermittent contact. You can easily identify plugs
crimped with one of the inferior tools. When viewed from the front, the middle con-
tacts are visibly higher than the contacts near the edge of the connector plug.
Recrimping rarely makes any difference, unless it is done with a proper crimp tool.
You should spend the extra money to purchase a high-quality crimp tool.
These tools are heavily constructed and will be quite a bit more expensive than the
low-cost tools. Some may have interchangeable dies for different sizes of modular
connectors. A high-quality crimp tool for 8-pin modular plugs should cost $100 to
$200, depending on additional features.
Bad crimps may also allow a wire to be pulled out of the plug contact area. The
same type of problem can happen in a cable termination at a workstation outlet jack
or at the patch or punchdown in the telecommunications room. These connections
are not made for very large pulling forces, and may fail when overstressed. User
cords in the work area are particularly subject to this kind of damage, because they
often are run along the floor in the path of chair legs, furniture, and feet. Always
inspect both cable ends of a cord that is suspected of having a bad connection.
Replace the cord if there appears to be damage.
A source of intermittent connections in modular plugs is the use of solid wire.
These plugs were really designed for stranded wire, and solid wire does not work
well. Special versions of modular plugs are allegedly designed to work with solid
