In the past, people used quad wire (or POTS wire) for their phone systems.
This wire is not twisted, is susceptible to interference, and is not suitable for telephone systems
with several lines. If you are updating an old system and you encounter this
wire, your best option is to replace the old wire with some type of twisted
pair wire, such as CAT 3 or CAT 5e, rather than expanding the system with
the quad wire in place.
Most installers have been using CAT 3 for phones, but CAT 3 is getting
harder to find, and the price difference between CAT 3 and CAT 5e has
narrowed considerably to around five dollars per thousand feet. CAT 3 is
still recommended for phones, but if there’s any chance that your phone
system may be used for data transmission in the future, an upgrade to CAT 5e
would be well-advised.
Aside from future-proofing, there is another reason that some people use CAT
5e for phones: simplicity of installation. If you are wiring for a computer
network at the same time that you are wiring for a telephone network and the
job is very large, you may find it easier to contend with one type of cable
rather than dozens of boxes of different kinds. There is truly nothing worse
in an installation than pulling a long run, especially one that requires
fishing through small conduits and around tight corners, only to find out
that you pulled the wrong cable.
There are a few installers who use CAT 6 for telephone systems. Unless the
phone network may be used as a computer network in the future, this is a
strange choice. It is the equivalent of using a speed boat to cross a
swimming pool or using a chainsaw to remove a small twig from a bush – it’s
very unnecessary, very expensive, and a big hassle for what you’re trying to
accomplish, but it will work. [Bethany Hunt of FOURPAIR]