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Home • Troubleshooting • Telephone Wiring - CAT5

Your phone Wiring - Do you need CAT5? (Updated 15-Nov-03)

One of the things you might start thinking about in chasing down 56k connectivity issues, is the wiring inside your home/business to the jack your modem plugs in to.

While the inside telephone wiring can be a problem, it rarely means you need to re-wire, or put in Category-5 cable. Note: If you are wiring a new house or installation, it may make sense to use CAT5 wiring for your telephone line(s) and for possible future in-home LAN. However - separate cable runs should be made for telehpone and LAN.

What is CAT5 wire:? Category 5 wire is 4 pairs (8 wires) inside an (unshielded) sheath. Each pair of wires is twisted throughout their length. The twist provides a higher immunity to noise and crosstalk compared to untwisted wire pairs.

I received a message asking why I make no mention of the "...poor wiring messes that are found in the average home." The writer goes on to say:

CAT 5
     Category 5 wire is high capacity telephone/data wire. Composed of 4 twisted pairs of high-speed wire. Carries telephone and data signals for phones, faxes and computer modems. Improves sound quality by reducing cross talk or buzz. Enhances high-speed  communications.

The fact is that once an analog (56k or any) modem's signal goes to the telephone wire, it is an analog signal with a bandwidth of about 150-3600hz. And because the telephone network uses balanced pairs - ie, neither wire is at ground potential, it is unusual to get impaired performance on ordinary untwisted copper 2-pair wire in most settings. In other words, I don't think most people need to run CAT5 wiring for their telephone lines to get the best performance out of the modem.

Inside wire trouble - Things that can cause a problem (and you'd probably notice them on voice calls as well) are poor splices or taps, or loose connections to outlets anywhere in the house. Any connection to ground is a no-no (you'd hear a bad hum). Other devices (fax machine, telephones, answering machines, etc.) can also cause a problem. The line cord you use to connect the modem to the phone jack can also be a problem. 

Here's what you can do to check and isolate any inside problems:
Try a different line cord from the modem to the phone jack.
Unplug all other phone devices on the line. If performance changes, plug them back one by one to isolate the problem. To verify it is a particular device and not the jack or the wire to the jack, plug the problem device into another phone jack, and check its line cord.

Last - before you go the step of putting in new wire, find the telco demarc. It normally is a box on the outside of your house. It should have a customer-accessible area with a modular connector - if you unplug the connector, all the wiring inside your house is disconnected, and the line is only available in that (now empty) jack. Run a line cord from your modem to that jack and test - if your performance doesn't change, you don't have a problem with your inside wiring.

In some cases, EMI (electro-magnetic interference) may make its way into your phone wiring. Sometimes it's as simple as the routing of the line cord from your modem to the jack. Other times it's more complicated - but the demarc test will pretty much tell the story: if connecting your modem to the demarc doesn't change the performance, your phone wiring isn't the limiting factor in the quality of your connections.

I've been asked, how would you wire your phone line(s) with CAT5 cable? CAT5 LAN modular connectors (RJ45) have 8 contacts (4 wire pairs); standard telephone jacks (RJ11) have 4 contacts (2 wire pairs).

If you have 1 phone line, simply use one of the pairs (Blue/Blue-white) in the CAT5 cable, and cut-off/leave all others unconnected. Connect the CAT5 pair to the R & G (red and green)-designated terminals of the standard phone jack.

If you have 2 or more lines, use one of the twisted pairs in the CAT5 cable for each line at the demarc(s), strip a foot or so of the sheath from the other end, and connect each pair to a separate RJ11 jack for each line. (You can connect to lines to a RJ11, and some multi-line phones, and adapters can be used to separate/use both lines. Some modems may not operate correctly if 2 live lines are connected to the modem line input - this can easily be prevented by using a line cord to the modem that has only 2 wires connected through to each end.)