Information Technology Reference
In-Depth Information
wire, and they do work better, but you will be much better off if you use only
stranded wire with these plugs.
In rare cases, modular connector jacks may not seat properly in the connector
faceplate. Some designs include the plug channel in the molded plate, with a sepa-
rate jack assembly that snaps into the plate. If the rear module is not seated prop-
erly, the jack wires may be too far back to properly connect with the plug contacts,
even though the plug clip seats with a sharp click.
In rare cases, modular jack pins may get crossed or bent. This will usually test
as a shorted wire from the far end and as an open connection from the near end.
The design of these jacks places the pins (which are really bent wire pins) in narrow
plastic slots so they can move as the plug is inserted. At the top of the tracks, most
jacks have an open area where the pins could slide from side to side if the wire pin
is pushed upward too far. If the pin is allowed to slip into another pin's track (either
during assembly or use), the pins will short together and one or both of them may
be prevented from making any contact at all with their corresponding plug contact.
If you suspect this problem, visually inspect the plate and replace the jack if it is
damaged. This defect tends to permanently bend the wire pin and you may have
continuing problems. It is a good idea to glance at the pins in each jack insert before
you terminate the station cables. This only takes a second, and will save you hours
of frustration later.
Modular jacks should be mounted so that the pins are on the top side of the
jack opening. The theory is that this keeps dust and dirt from contaminating the
pins. Jacks are also available with dust covers, which should be left in place until
the jack is used and replaced when a plug is removed.
A punchdown block or patch panel punch block is a special type of connector.
Some older-style 66M punchdown blocks require the use of a metal clip to connect
between contacts in different columns. The standard 66M block has four columns of
contacts across each punchdown position. Generally, the contacts are internally
wired as pairs, so that Column 1 and Column 2 contacts are connected in common,
as are Column 3 and 4. However, some connectorized designs make all four columns
independent, so that a clip must be placed across the contacts in adjacent columns to
complete the circuit. A missing clip will cause a problem with the circuit.
An additional problem with punch blocks of any type concerns the use of
stranded wire. These side-displacement or insulation-cutting terminals are designed
for solid wire only. Do not use stranded wire with these blocks. The wire may not
make good contact, because the contacts press in from the side, instead of clamping
the wire or piercing into the strands. Even if an initial contact is made, the wire may
pull free more easily, because much of the strain resistance of the contact depends
on trapping a solid wire in the contact.
