When checking wire indicated as "telephone" wiring, there is an industry standard color code used by technicians to install telephone type services - that is, telephone set jacks, jacks for modems and fax machines and jacks for other types of devices which might be utilizing "telephone" service such as answering machines or auxiliary audible or visual signals.

One pair of wires is needed for a dial-up "telephone" line. Industry terminology for these two wires is Tip and Ring.  The wiring is usually referred to as IW, for inside wire, though, most wires can be used out of doors and will give many years of service.  This being said, it must also be stated that the wiring will not stand the ravages of time particularly of the sun's ultraviolet light which dries out the wiring's outer jacket causing it to crack in time and thereby letting in corrosion-causing moisture.

Let's talk about testing a telephone line.  For reference, the Tip side of a phone line is "ground," or negative - the Ring side is called "battery" and is positive in nature like the battery of your car and which carries the dial tone.

The type of meter used to test phone lines is a simple Volt-Ohm meter.  These can usually test for AC and DC current and resistance.  Most test meters will have a common lead which is usually black in color.  The second lead which will be used on either the DC scale of the meter or on the Ohms, or, resistance, scale is usually red in color.  To "read" a telephone line you will use both the DC scale and the Ohms scale.

The black meter lead is usually put to a "ground" source such as a cold water pipe, an electrical conduit, the ground lug of an electric outlet, a radiator or any other source which is grounded.

For those not familiar with the term, "ground" means essentially the same thing as what's in your backyard - ground, earth, dirt, et cetera.  In a pinch, if you find you're on a concrete slab outside, such as might be in a garage, and no ground source is readily available, often, putting the a meter lead to a metal bar of some kind, preferably made out of iron, and then putting the bar on the concrete will be sufficient to obtain some kind of a reading - though it may not be 100% accurate - but it should suffice to identify the two sides of a phone line.

Now the foregoing was the setup to identify, or "read," what is on either side of a phone line. If you set the meter on a DC scale of at least 50 volts and clip the meter to both sides of the phone line (that is, one lead to the Tip and the other to the Ring side), one of three things will generally happen.

If you were to look at a telephone company central office line, coming to your premises, using a simple volt-ohm meter, here is what you would see.  Assuming the meter is turned on, you will get either:

* no reading on the meter,

* the meter needle will "bury" to the left side of the scale in a very sharp movement,

* or, you will get a reading on the meter of about 50 volts DC - hopefully - though it may be less.

When a phone line is "off-hook" the reading on the meter will be about 6 volts DC - give or take a volt or so.

If you are trying to "read" a dial-up phone line other than one originating from your local telephone central office - as, for instance, from a business switchboard or telephone system, you might read anywhere from 20 volts DC up to maybe 90 volts depending on what type of equipment is in the particular circuit under test.

But, for regular, ordinary plain old telephone service (POTS) lines, an ON HOOK reading will generally be around 48-52 volts.

If you are going to identify the Tip and Ring sides of the line, the black or common lead of the meter is put to a ground source.

First set the meter scale to at least a 50 volt DC range (your meter will probably have as the only available scale, 100 volts - ranges may be, for instance 5 volts, 10 volts, 25 volts and 250 volts - it depends of the meter.

Then, take the red lead and touch it in turn to the two sides of the pair of wires (ignoring color code at this point) and one of them should give you a reading.  That one is the "battery," the "positive" or "Ring" side of the line.  You will not get a reading on the other telephone wire lead.

If the phone line is not OFF HOOK, that is, no one is on the phone, you should get a reading of somewhere around 50 volts DC.  If not, recheck your connections and your ground source.

If the reading is significantly below 50 volts (such as less than 40 volts) then there is a problem between the telephone company central office and the meter which could be in either the telephone company facilites to your premises or in your premises or jack wiring.

Next, disconnect the meter from the pair of telephone wires and set the meter to the Ohms scale.

On most meters, you can "Zero Adjust" the meter by holding the red and black leads together and then turning a wheel until the meter needle sits on Zero.

Once that is done, again connect the black lead to a good ground source and the red lead to the second wire of the telephone line.  The reading now on the meter will be almost to the Zero on the scale or very close to it.  If it is not, recheck your connections and ground source.  If the reading is still poor, there is a problem with that side of the line.

If the readings are not acceptable, the next point to check the phone line is at the telephone Network Interface (NI).  If there is no Interface, you may have to check the line at any point you can gain access to it (without going into the telephone company terminal in or on the back of your building) or at the lightning protector if you can find it.

Redo your testing from any of these points and if you still have trouble, you will have to notify your local telephone service provider to have the trouble fixed.

If you have a Network Interface, there are testing instructions inside the NI.  If you are not getting a good reading at that point, then the trouble is in the local telephone company facilites and you should notify them for repairs.  There will be no charge for the repairs.

If, however, you are getting a good reading at the Interface (or, if you have plugged a known, good telephone into the NI jack and got dial tone), then the trouble is on your premises.  If you call the local telephone company, there will probably be a heavy charge to fix the trouble - if it can be fixed.

If there is no Network Interface, the telephone company should NOT charge you for a visit to isolate the trouble and they should put in a Network Interface for future use.  There should be NO charge for this.  Always be sure to ask them though to avoid unforseen charges.

There are, and over the years, there have been, different types of wire used for telephone type service.  These differ in the number of pairs of wires contained in an outer jacket which may be gray in color, or anyone of a number of other colors - cream, pink, brown (for older wire from the 50s) and in some cases white.  But mostly it'll probably be gray.

If you see or hear a reference to the "category" of the wire, it will usually be associated with a number such a 3 or 5.  Most of the time when this comes up, it will be because someone says "Cat 5 wire" - which means category 5 wire.  Most ordinary phone wire is category 3 - this is industry standard and is suitable for all sorts of services including DSL and under some circumstances even DS1 (T1).  For the latter, it greatly depends on how it is installed and how many DS1 lines are involved.

The category of the wire has to do with the twist in each pair of wires. Cat 3 wire has LESS twist than Cat 5.  The twist of the wire has everything to do with breaking the power influence from one pair to another due to the magnetic field which surrounds every pair of wires.  This is why for DS1 (T1) Cat 5 might be more desireable than Cat 3.  But, even then, to properly ensure good service to DS1, shielded wiring should be installed if multiple DS1 lines are going to be used.

If you are dealing with VERY old wire, such as might be found in an old home, it might be a three strand wire and is generally referred to as bridle wire.  This might be plastic coated and brown in color or if of the outdoor variety, it might be jacketed in neoprene and is black in color.  An older variety of the plastic coated wire is a lacquer-coated cloth insulation on the wire which was brownish in color when new (were talking the 1920s and 30s here).  Bridle wire was coded under the cloth insulation.  The indoor wire (cloth insulation and plastic) had red, green and yellow filaments under the jacket, or, insulation which covered each lead.

The outdoor neoprene wire had ridges molded into the insulation of each individual lead to differentiate one lead from the other.  If you "skin" back the insulation on much of this kind of wire, you may see a coloring on the copper wire itself - again either red, green or yellow.

The color codes for modern wire is part of the wire insulation coating itself which is under the usual gray outer jacket.  Here are the color codes for the most common types of wire you're liable to come across.  The first color of the pair is the Tip side of the line, the second, the Ring.

2 Pair Wiring Colors and Line Polarity (i.e., 1^st line, 2^nd line, etc.)

Green/Red - Ground/Battery - 1^st line

Black/Yellow - Ground/Battery - 2^nd line

3 Pair Wire (older variety)

Green/Red - Ground/Battery - 1^st line

Black/Yellow - Ground/Battery - 2^nd line

White/Blue - Ground/Battery - 3^rd line

3 Pair Wire (newer manufacture)

White/Blue - Ground/Battery - 1^st line

White/Orange - Ground/Battery - 2^nd line

White/Green - Ground/Battery - 3^rd line

4 Pair Wire (following Battery and Ground applications as above and usual line assignments)

W/B - Line 1

W/O - Line 2

W/G - Line 3

White/Brown - Line 4

These are the types of wire you likely to run across.  There are many types of multi-pair wire besides the ones given above.  There are also 6 pair, 12, 16, 25, 50 and 100 pair wire which might be found.

THE COLOR CODE FOR ALL THESE IS ALWAYS THE SAME.

In multi-pair wiring the color code is arranged in groups of 25 pairs of wire.  For wiring of more than 25 pairs, each 25 pair group of wires is "binded" with an identifying color using the same colors as used for the pairs in the binder group. 

Here is the color code for a 25 pair IW cable.

Ten colors are used in the Color Code.  The Tip or Ground colors are White, Red, Black, Yellow and Violet.

The Ring, or Battery colors are Blue, Orange, Green, Brown and Slate (gray).

These colors are repeated over and over in different binder groups using different binder colors following the same sequences as the pairs.  Using this system, cables consisting of thousands of pairs can be easily identified; that is, the first binder group of 25 pairs will be binded with a Blue/White strip (remembering the first pair is also Blue/White); the eleventh binder group of 25 pairs will be binded with a Blue/Black strip and so on (the eleventh pair in all binder groups would also correspond to colors Blue/Black).

In a 250 pair cable, for example, pair number 211 would be identified as the Brown/Red binder, Black/Blue pair - the 201^st pair being Brown/Red binder, Blue/White pair and so on.

If this seems too confusing and you have any questions, email me or give me a call.

Most technicians, when reciting the colors, will usually give the Ring color first and then the Tip, and I'll follow that from here on, but, however they say it, or, however it's written, the color tells the side of the pair and its function, i.e., polarity.

25 Pair cable

1^st five pairs - Blue/White, Orange/White, Green/White, Brown/White, Slate/White

2^nd five pairs - Blue/Red, Orange/Red, Green/Red, Brown/Red, Slate/Red

You will have noticed that the Ring colors repeat every five pairs, but, the Tip colors change.

3^rd five pairs - Blue/Black, O-Bk, G-Bk, Br-Bk, S-Bk

4^th five pair group - Blue/Yellow, O-Y, G-Y, Br-Y, S-Y

5^th group - Violet/Blue, Violet/Orange, V-G, V-Br, V-S

You'll notice that in that last group I gave the Tip color first rather than the Ring. But, nevertheless, as I said, the colors retain their industry standard intended function regardless of how they are given.

In a 50 pair cable, there will be two binder groups of 25 pairs each.  The difference (besides being a larger cable) is that each 25 pairs is wrapped with a binder color.  The first binder will be wrapped with a Blue/White ribbon, strip or marker, also called a tracer; the second will be wrapped with an Orange/White binding.

The binding colors follow the regular 25 pair color arrangements as used on the individual cable pairs.  The third binder of 25 pairs is Green/White and so on for whatever the size cable.

This arrangement can handle up to a 625 pair cable.  Unless you're getting into "feed" cables, such as the phone company uses underground or strung on telephone poles, we don't have to get into binder markings for larger cables.

This just about covers it.  If some other question comes to mind, please don't hesitate to send me an inquiry using the contact information in the sidebar.