TELEPHONE – CABLES & CODES

TELEPHONE CABLE HISTORY

From 1876 to 1888, there were a number of different types of cables used, and no real format to them.  In 1887 a conference was held between a number of the different companies to establish standards.  So, 1888 brought the first telephone standards.  For the telephone cables this meant a pair of conductive wires for each phone service, the wires were 18 gauge copper and twisted around each other, the start of the “twisted pair copper cable”, which is still the format for telephone cables today.  The outside sheath was made of a lead/tin alloy, and the insulation was made of oil-soaked cotton.  The biggest cable was a 52 pair.  In 1891 the insulating material was changed to strips of waxed paper.

These lead cables were identified only by their pair count and gauge.  A cable marked as “51-17” was a 51 pair cable, with 17 gauge conductors.  A 26 pair cable with 26 gauge wire would be listed as “26-26”.

A young trainee on the telephone switchboard in 1951.
A lead aerial cable with a pre-molded splice case. Most lead cables had splice cases that were hand-soldered.
A small lead cable in a manhole that has been cut off.

Beginning around the late 1940’s, that outer lead was now removed and replaced with various plastic coverings.  The paper insulation remained, so the name “paper cable” is often used to identify them.  Paper cables have a paper mulch insulation of the tip and ring wires, an outer polymer (plastic) jacket, and just like lead cables they were “air core”, meaning they had no filled interior.  Paper cables are also commonly referred to as “pulp cables”, but they mean the same thing.  These paper/pulp cables were manufactured from about the late 1940’s up to 1958.

Paper cables were still used inside of the Central Office.  The fact that they were prone to moisture damage was not a problem because they were contained only in the dry vault area of the CO.

 

In 1958 came the PIC cable, Polyethylene Insulated Cable.  Many technicians also refer to them as Plastic Insulated Cable.  For the first time there was a true separation of sheath and jacket.  The inner sheath was an aluminum-steel alloy in a corrugated form.  The outer jacket was polyethylene.

PIC cables were also gel-filled.  Their interior is filled with a jelly-like substance to prevent serious water damage if the cable is slightly damaged on the outside.

The 25 pair would become the smallest cable.  If the pair count is marked as “6”, then it is a 600 pair, not a 6 pair.  All larger cables would have pair counts that could be multiplied by 25, such as 50, 100, 200, 600, etc.  A few cables are even produced with pair counts of 75, and 175.  The largest cable produced was the 2400 pair.

Those pairs are then combined into bundles of 25 pairs, technically known as binder groups. Telephone cables are always referred to by their pairs so there are always twice as many conductors in the cable as the pair count indicates – a 200 pair cable has 400 conductors, but is always called a “200 pair”. Those pairs are then combined in to bundles of 25 pairs per bundle, so a 200 pair cable has 8 binder groups.

Working on an aerial paper cable in 1954.
An advertisement of the new PIC cable in 1960.

4 TYPES OF PHONE CABLE

Overall, phone cables have had a vast number of changes over the years, and phone cables are often identified by their use (the “C” codes) instead of their type, but you can actually simplify most phone cables into just four basic groups: Lead, Paper, PIC and T-Screen.  They first three are all “twisted pair copper cables”, but there are several differences between them which can be summarized here.

 

LEAD – Produced from 1888 to the late 1940’s.  The insulation material within the cable was a mulched paper (pulp) which insulates every tip and ring wire, the outer sheath/ jacket is lead including the splices.  Many lead cables are now pressurized (with an accompanying air hose), and lead cables are usually found only in duct runs, though there are exceptions.  On phone prints they are usually indicated in the old number code, such as (51-22 or 51-26).  The first set of numbers was the pair count, while the second set of numbers was the gauge of wire.  Some of them may be indicated on the prints in the newer 4-letter code starting with 2-Xs and always ending with the letter “L”, such as XXTL.  Lead cables do not have any printing on the outside of the cable.

 

PAPER – Also known as PULP cables.  They were produced from the 1940’s to about 1958, though there were a few still being installed in outside plant (OSP), up to the early 1960’s.  They have the same basic construction as lead cables, but with a plastic outer jacket instead of a lead sheath/jacket.  They have colored insulation on the tip and ring wires, but it is not an individual color coding.  Most paper cables are now pressurized (with an accompanying air hose), and paper cables are usually found only in duct runs.  Paper cables were the first to use the 4-letter code, and on phone prints they are shown with the 4-letter code, and usually with the letter “D” in the second position, such as HDBF or ADKA

 

PIC – Polyethylene Insulated Cables have been the only phone cable since 1958.  Their tip and ring wires all have individual color coded plastic insulation within a specific bundle, so all 25 pairs in a bundle have individual color codes, then each bundle tape has a different color code.  PIC cables are the only phone cables that have plastic insulated conductors, though you would typically never see the exposed interior of a lead or paper cable anyway.  PIC cables have a steel/aluminum sheath around the conductors, and a polyethylene outer jacket.  This is referred to in the 4-letter code as though the sheath and jacket were one and the same, so they are labeled as having a sheath of aluminum/steel/polyethylene, or with an acronym for the three such as ASP.

PIC cables are produced in pair counts of 25, so their sizes are 25, 50, 75, 100, 200, etc.

PIC cables are indicated on phone prints with the 4-letter code, such as ANMW.  All modern cables are PIC cables and they are found in duct runs, phone pedestals, AP’s, aerial cables, DSL cabinets, and connecting to load coils and repeaters.

The PIC cable has an aluminum/steel sheath inside the poly jacket.
All PIC cables have their pair count number printed on the outside of the jacket.

T1 – T-Screen – T-Screen cables are used in the T-1 through T-3 systems.  They are produced in pair counts of 26, 54, 106, and 210.  They have some similarities to PIC cables except that their tip and ring wires are not twisted together, but separated, all tip wires are bundled together, and all ring wires are bundled together.  T-Screen cables are very noticeable in pedestals because of the aluminum wrap around the two bundles

T-screen cables have an aluminum wrap inside the poly jacket which is usually very noticeable on the cables inside of pedestals.

PRESSURIZED CABLES

Both lead and paper/pulp have an inherent weakness in outdoor applications.  Any damage or excessive wear on the sheath can easily allow water inside the cable.  Although both lead and paper cables had paper insulation, the paper itself was never the true insulation.  It was the air in and around the paper that provided the insulation.

PIC cables and T-Screens have a gel-filled insulation, so when PIC cables were introduced, it then became the standard to refer to the lead and paper cables as Air Core Cables.  The gel-filled insulation of PIC cables naturally prevents moisture from entering the cable.  However, the paper/air insulation not only can not prevent moisture, it actually attracts moisture if it is damaged.  That paper/air insulation reacts like a paper towel and soaks up any moisture touching the cable.

The answer was found in forcing dry air into the cable at different points.  An air dryer/compressor forces air into a small air hose which runs the length of the cable.  At various points the air hose will connect into the cable.  This way the air is not forced in at just one end of the cable, but instead at different areas of the cable which is much more effective.  As long as the air pressure exceeds the psi of surrounding water, which is usually no more than 5 psi even in 10 feet of water, the air will keep the water out.  Since phone companies want to ensure that the cable stays dry, even in the wettest season of the year, most will use a 7.5 psi as a standard minimum pressure.

Pressurized telephone cables are accompanied from manhole to manhole with an air cable that connects in to the phone cables, usually at each manhole.
Checking the air pressure on a phone cable in 1958.
Notice the air cables on the upper right of the manhole.
Sometimes the air cables are accessible closer to the manhole lid.

All of the air cables must connect to a dryer/compressor somewhere along the line.  This is usually at the CO, but on rare occasions you may come across a dryer/compressor along the duct run, and probably very near a manhole lid, where there will be an aboveground dryer/compressor, probably operated by a generator.  The compressor is set to kick on when ever the pressure drops below 7.5 psi.  This is of course not a lot of pressure, but enough to do the job.  The air hose will come from the compressor into the manhole, where it will make its’ first connection onto the cable.  Then it will follow the cable through the duct run, making more intermittent connections as it goes.  The connection from the air hose to the cable is called a manifold, though it actually looks more like a bicycle tire valve.

A paper cable on the upper right is noticeable because it has an old metal splice case...
...but mainly because it is fed by an air cable in to the manifold of the splice case.

The air hose is also quite commonly referred to as an “air cable”.  Neither term is really accurate since the “air” being pushed into the hose is more nitrogen than oxygen.  All of the older air hoses were strictly made of rubber, but later on they were produced with an aluminum inner sheath.

 

TELEPHONE COLOR COMPASS

Since telephone cables can be quite numerous in a pedestal or cabinet, it is very helpful for the phone technicians to know which cable is going which way.  The answer was for technicians to begin a color code for each direction.  Then they could simply wrap some colored electric tape around the cable within the cabinet, or possibly used some colored plastic ties, and more easily know for sure the direction of the cable.  This system has been used quite often, mainly by telcos that were part of the Bell System, but it is not a guarantee of direction.

NORTH – ORANGE

EAST – GREEN

SOUTH – BROWN

WEST – SLATE

The color compass can be easily remembered using the phrase Only Good Boys Succeed.  Starting at north – and going clockwise: O – G – B – S.

The cable with the green plastic tie runs in a general easterly direction. The other cable has both a blue and slate colored tie. This means it runs to the west, and that it is coming from the CO.
One cable on the right has an orange tie, which means it runs to the north out of the pedestal. The cable with the green tie runs to the east. The cable on the left has a blue plastic tie, so we know it runs to the CO, Yet, it also has an attached label stating that it runs to the east, so the CO is to the east.
The blue tape tells us only that the cable is coming from the Central Office. In other words, it is the "in cable".
A white marking on a cable means it is the cable that connects to a load coil. If the load coil is not visible aboveground, then it is buried beneath the pedestal.

There are also two more colors used to give information on cables.  The color blue indicates the cable that is headed towards the Central Office.  The other color is white and indicates the cable that connects with a load coil.  That load coil may be aboveground or belowground.

Central Office – Blue

Load Coil – White

 

 

THE NUMBER CODE

Lead cables 1888- c.1949

The original coding system for telephone cables was used on phone prints but not on the cables themselves.  They consisted of two sets of numbers, such as 26-22.  The first number indicated the pair count, while the second number indicated the gauge of conductor used.  In this system a 26-22 was a 26 pair cable with 22 gauge (size) conductor wire.

Wire gauge is actually opposite of what it might first seem – the higher the gauge number, the smaller the diameter.  Over the years the cables were often produced with smaller and smaller tip and ring wires, and this shows in the increase in number for the wire gauge.

 

1st set of                             2nd set of

Numbers*-                        Numbers-

Years Produced              Pair Count                    Gauge                          Sheath  Insulation

1888-1891                                 52                                        18                           lead/tin oiled cotton

1891-1892                                 52                                         19                           lead/tin waxed paper

1892-1895                               100                                        19                           lead/tin waxed paper

1895-1896                                152                                        19                           lead/tin waxed paper

1896-1896                                180                                        19                           lead/tin waxed paper

1896-1901                                 208                                       19                           lead/tin waxed paper

1901-1912                                  303                                       19                           lead/tin waxed paper

1901-1902                                 404                                       22                           lead/tin waxed paper

1902-1912                                  606                                       22                           lead/tin waxed paper

1912-1958                                     26                                       22                lead/tin/antimony   waxed paper

1912-1958                                     51                                        22                lead/tin/antimony     waxed paper

1912-1918                                   303                                        19                lead/tin/antimony     waxed paper

1912-1930’s                                909                                        22               lead/tin/antimony      waxed paper

1914-1930’s                                 1212                                      24                lead/tin/antimony      waxed paper

c.1915-1958                             26 & 51                                     24                lead/tin/antimony      waxed paper

1918-1930’s                                   455                                       19               lead/tin/antimony      waxed paper

c.1925-1958                           100 -1200                                  24                lead/tin/antimony       waxed paper

1930’s – 1958                         100 – 900                                  22                lead/tin/antimony       waxed paper

c.1940-1958                            26-51-100                                  26               lead/tin/antimony       waxed paper

c.1940-1958                            26-70-100                                  19               lead/tin/antimony       waxed paper

1942                                                    54                                       19               lead/tin/antimony       waxed paper

——————————————————————————————————————–

1950’s                                      26 – 51 – 400                              22                      alum/poly           waxed paper

1950’s                                               2400                                     26                      alum/stl/poly      waxed paper

 

THE 4-LETTER CODE

PIC Cables (and many Paper cables) – 1958 to present

This code is used on phone prints, and has also been stamped onto the modern PIC cables.  The vast majority of cables using the 4-Letter code are PIC cables.

Paper cables have been labeled with the 4-letter code on phone prints, but not on the cables themselves.

Also, many old lead cables have been relabeled on some phone prints using the 4-letter code, but always beginning with the letters “XX”.

With the 4-letter code, the pair count will always follow the code, such as: ANMW – 2, but if the number is only a single digit then it is an indication of a number that should be followed by 2 zeros.  Therefore, an ANMW-2 indicates a 200 pair cable.

 

1st Letter                                     2nd Letter                                      3rd Letter                             4th Letter  

Cable Design                      Conductor Insulation                     Conductor                           Sheath

A – PIC waterproof            B – Polyethylene PVC                      J – 13 gauge/copper         A – Alpeth (aluminum &

       Or Pulp air core                                                                                                                              Polyethylene)

B – PIC air core                  C – Foam skin /                               H – 16 gauge/copper         C – Stalpeth (steel, alum-                                                                                     Polypropylene                                                                                     inum & polyethylene)

C – PULP or High               D – Paper Cable                               C – 17 gauge/alumin          D – Lepeth (lead &

       Waterproof                                                                                                                                         Polyethylene)

D – PIC Steelpeth or            F – Foam skin / Dual                      B – 19 gauge/copper          E – Polyethylene

Ductpic types                           expanded Polyolefin                                                                           Jacketed lead

K – Screened Core               G – Solid Polyolefin                          D – 20 gauge/alumin        F – Polyethylene jacketed

 

L – Low Capacitance           H – Solid Polyethylene                      A – 22 gauge/copper        G – PAP (polyethylene

                                                                                                                                                                     Aluminum)

M – Low Capacitance           J – Solid Polypropylene                    F – 22 gauge/alumin        H – PASP

Jelly filled

X – Lead Cable*                       K – Solid Polypropylene                   M – 24 gauge/copper        J – TOLPETH J

 

                                                  L – Dual expanded                            K – 24 gauge/alumin       K – TOLPETH K

Polypropylene

                                                R – Dual expanded                               T – 26 gauge/copper       L – Lead Cable

Polypropylene

                                                N – Dual expanded                               W – 28 gauge/copper       M – Alvyn

Polypropylene

                                                X – Lead Cable*                                                                                       N – Stalvyn

 

                                                                                                                                                                P – Reinforced self-

                                                                                                                                                                           support

 

                                                                                                                                                                 R – ARPETH

               

                                                                                                                                                                  S – Self-supporting

 

                                                                                                                                                                   T – ARPAP

 

                                                                                                                                                                    U – ARPASP

 

                                                                                                                                                                     V – STEALPETH

 

                                                                                                                                                                      W – ASP

                                                                                                                                                                       X  – Abandoned **

                                                                                                                                                                       Y – Bonded ASP

                                                                                                                                                                        Z – Bonded STALPET

 

(*) Any cable with a 4-Letter code that begins with two X’s is a lead or paper cable, and almost always a lead cable; such as XXTL.

 

(**) When a PIC cable is abandoned, the last letter is sometimes changed on the prints to an “X” indicating that it is no longer in use, such as BKTX.

 

ARMORED CABLE CODES

In addition to the 4-Letter code, there may sometimes be another 2-Letter code shown after the pair count, such as: BKTA – 200 – BT.  The last two letters, BT, indicate that this is an armored cable.  The PIC cables were much more susceptible to damage so some high-profile PIC cables will have an armor coating.

Gophers can easily chew through a PIC cable.  This doesn’t happen very often, but it does happen.  Today most cables that run up a pole to an aerial line are protected by plastic or metal conduits, known as riser guards, but the conduit never covers the entire cable, and these were sometimes being chewed on by squirrels or damaged by vandals.  Certain buried cables that were used for airports or military bases could not afford to have the lines go down just because of a hungry gopher.  The armored cables were created to provide these high-profile services with all possible protection.  Below are the 2-letter codes for the 4 different types of armored cables.  The UM cables are commonly used for military installations.

Three phone cable. The PIC cable is in the center. The other two are armored cables of different kinds.
Armored telephone cable.
Armored telephone cable laying exposed on the beach where it crosses the river.

                       AT – Aerial Tape Armor

                        BT – Buried Tape Armor

                        MP – Mechanical Protection

                        UM – Unsoldered Mechanical Protection

 

THE “C” CODES

These might be called “C” codes because each of them consists of a number, or numbers, followed by the letter C, but actually the “C” simply means code.  This idea came from the municipal water departments who had originally devised a series of C-codes for water pipes and activities.  Just like water pipes, these phone C-codes can in some cases be related to the type of material, but their main purpose is to identify the actual use of the cable, such as an aerial cable running pole to pole.

This “C” code was applied to fiber lines when they were first being installed in the early 1980’s, and was partially meant to quickly identify fiber lines from the old copper lines.  However, the anxiety over the possibility of damaged fiber led the phone companies to make sure the fiber was clearly identified on the prints with something more than just a simple “8C”.

Many telephone prints will show only one set of codes or the other.  They may show only the 4-letter code, sometimes with just an additional “B” for the buried cables, while more simplified prints may only show the “C” codes, probably with “F/O” for the fiber lines.  Most phone prints that have been modernized to a cad file will probably show both codes so the viewer can easily identify both the use of the cable, and its’ material and gauge.

                        4C – Conduit (may be an empty conduit for future use)

                         5C – Cable in Conduit (cable was pulled through the conduit as soon as it was placed in        the ground)

                         6C – Submarine Cable (placed under water such as a lake or river)

                         8C – Fiber Optic Cable               

                        12C – Aerial Cable

                        14C – House Cable

                        25C – Trunk or Toll Cable

                        45C – Buried Cable

                        52C – Aerial Cable

                         62C – Cable inside building

                         85C – Buried Fiber Optic Cable

                         812C – Aerial Fiber Optic Cable

                        825C – Trunk or Toll Fiber Cable

                        845C – Direct Buried Fiber Cable