Information Technology Reference
In-Depth Information
Occasionally, a connector block open can occur when the punchdown tool cuts
the cable end of the wire being terminated, rather than the scrap end. A tool may
sometimes cut an adjacent wire to the wire being terminated. It is a good idea to
check the terminated wires to be sure none seem loose. Cut or loose wires should be
reterminated.
Coax cables are subject to having their connections pulled open by connector
stress. Crimped or soldered center conductor pins are fairly sturdy, but the pin may
sometimes be pulled back into the connector body and not make contact with the mat-
ing jack. A visual inspection will show a pin that seems too short. The center pin should
be approximately even with the edge of the shield sleeve (not the bayonet sleeve).
Cables that are pulled on while mated may also break the shield wires. If a
coax shield is improperly stripped, many of the tiny wires that form the braid will
be severed, with only a few remaining to make the connection. When pulled, these
last few wires will break easily, leaving an open. The proper solution is to cut off
the end, prepare the wire properly, and replace the connector.
Any coax LAN wiring that uses BNC-Ts or terminators may be subject to opens
due to failure of the T or terminator. As a matter of fact, many technicians consider
the T component to be the primary cause of coax network problems. The connector
may fail by literally falling apart, or it may exhibit intermittent connections that just
add to the frustration. Low-cost connectors are the worst offenders. You would be
wise to use only high-quality connectors, Ts, and terminators on these systems.
Wrong Pin-Out.
All of the wiring problems that we discussed in the test equipment
in Chapter 15 are common failures of cable links. Among these are reversing the
order of some of the wires, crossing two pairs, flipping the wiring order, splitting
pairs, and total miswires. Reversing the order occurs in pairs. A common mistake is
to reverse the primary and tracer colors of a single pair. Another common mistake is
to mix up the green and brown pairs, or split these pairs, since the color difference
may be subtle in some cable. If you try to count pin numbers in a modular jack, be
sure to position the jack correctly (see Chapter 6). Flipping the wiring order of a user
cord is a common error with flat (silver satin) telephone-style wire. Of course, you
should never, never, never use flat cable for LAN wiring cords. Never.
Inspect the wiring order by holding both cord ends side by side. The colors (to
the extent you can see them) should be in the same order straight across the plug.
Better yet, use a cable checker.
The standard color code for 4-pair cables should be followed in wiring all jacks
and telecommunications room terminations. This code is different for punchdown
blocks and modular jacks. Modular jacks actually have two color code standards,
T568A and T568B. You must use the same standard throughout a horizontal cable
