The Basics of Telephone Wiring
by H Gregory
There is a widely held misconception that telephone wiring is an impossible
feat for the average non-technical person. The fact is that small wiring jobs
in your house or small business can be much easier than you'd expect, much easier
than shelling out exorbitant hourly fees to the phone company. If you can figure
out how to wire speakers for your new stereo, you can easily wire your home
or small office for your new phone system.
Wires, plugs, and the network interface
The basics of the wiring is pretty easy to understand. Most telephone wires
are one or more twisted pairs of copper wire. The most common type is the 4-strand (2 twisted pair). This consists of red and green wires, which make
a pair, and yellow and black wires, which make the other pair. One telephone
line needs only 2 wires. Therefore it follows that a 4-strand wire can
carry 2 separate phone lines. The twisting keeps the lines from interfering
with each other. If you need to run more lines than just 2, you may want to
use a 6-strand, or higher. Telephone wire comes in 2 gauges, 22 gauge and
24 gauge, 24 gauge being today's standard.
There are 2 types of common modular plugs, the RJ-11 and the RJ-14. The most
common is the RJ-11 which uses only 2 of the wires in a 4 (or more) strand
wire. This is the same kind of plug that you use to plug your telephone into
the wall. This is a 1-line plug. The RJ-14 uses 4 wires and is used to
handle 2 lines, or 2-line phones.
The first step
The first step to a small wiring
job is to figure out what the telephone company has left you to work with. What
kind of network interface (NI) do you have? They have probably left you either
a punchdown block or a network interface box. If there is a punchdown block,
and you can't get the phone company to install a modular jack for each Plain
Old Telephone Service (POTS) or central office (CO) line, then you will need
a punchdown tool to connect your inside wiring to the NI. Most new installations
consist of a network interface box. This has modular test jacks (where you can
plug a phone in to see if the line is live) and a terminal strip from which
you run your internal wiring (IW).
From the NI you want to plan how you want the wiring in your location to be.
The star (or homerun) method is the most common method of wiring. Each extension
or phone jack is run directly from the NI or phone system if you are installing
one. The other type of wiring is called the series (or loop) method. In this
method one long wire links all of the extensions in a series. This loop method
is not widely used anymore. As with the old type of Christmas lights, if one
goes out, all of them go out.
Using the star method, you are obviously going to have a few wires coming from
your NI, as you will have one wire for each of your plugs. You may want to simplify
the wiring and cut your wire costs by having few of the wires carry more than
one line or extension.
Let's take a 2-line installation as an example. Each pair that comprises
each of your POTS lines should be labeled.
One of the wires of your POTS line is called the tip wire and the other is
the ring wire (see chart). There are quite a few possible combinations of colors
that could make up your pair. So in order to connect your line to a modular
jack, you need to connect the tip wire of the POTS line to the tip wire of the
jack, and also the ring wire of the POTS line to the ring wire of the jack.
In a modular jack you have red/green and yellow/black. Most of the time you
only use the red/green pair. The green wire is the tip and the red wire is the
ring. Using the chart, figure out which of the POTS wires is the ring and which
is the tip, and connect them appropriately.
If you are not using a phone system and just want to connect your phone jacks
directly to the POTS lines, all you need to do is run wire from the NI to your
extension jacks. (This works the same way when you're connecting the extension
jacks of your phone system to your extensions.) Just connect the correct colors
to run the wire. Again, connect tip to tip and ring to ring. As long as you
are following the tip-to-tip rule, the fact that you are connecting a white
wire with brown stripes to a green wire and a brown wire with white stripes
to a red wire shouldn't be confusing.
Remember that in order to reduce the work and materials, you may run 2 or
more lines within 1 wire. At the end of the wire you can break out the 2
lines using an adapter which allows you to connect line 1 to an RJ-11 plug
and line 2 to another RJ-11 plug, or if you have a 2-line phone,
you can just plug an RJ-14 plug into the phone.
If you are using a small PBX or phone system, most likely the POTS lines (commonly
called trunk lines) are connected to the system using RJ-11 plugs. If your NI
terminates with a modular jack then the job is simple, just connect the phone
system using RJ-11 plugs. If your NI has a terminal strip (a place where the
pairs that comprise each POTS line terminate at a junction where you directly
connect the colored wires) then you would need to either connect the lines directly
to the PBX or connect a modular jack to each of the POTS lines on the strip.
Then, to wire your phone jacks, you follow the same procedure as noted above
for connecting POTS lines directly to phone jacks.
There really isn't much else to know. If you follow these simple instructions
you should have your phones working perfectly.