CABINETS, CROSS CONNECTION No's 1, 2 and 3


IPOEE Article on Subs Cable Distribution - 1939
IPOEE Article on Subs Cable Distribution - 1944

Initially wiring was all overhead, but as more people went on the phone the number of aerial cables became obtrusive and heavily congested.

Multi-core cables then came on the market and the overhead wires were moved to an underground network of cables.  These cables were fed from the exchange and smaller cables were connected to these cables as they radiated away from the exchange.  These cables provided no real flexibility as each division was a joint. 

Before the second world war flexibility in the cable network was afforded by the use of "multiple teeing" and "auxiliary joints" and in towns cable distribution heads were used.  These distribution heads consisted of water tight iron casings, which could be opened, but re-routing a cable was still difficult and working on the case could cause faults on other lines.  Distribution heads are pictured to the right.

Multiple teeing is a system where a proportion of the cables pairs from the exchange Main Distribution Frame (MDF) are teed together at joints and so are connected to more than one Distribution Point (DP).  This system is termed "non-tapered cable", that is, the main cable does not reduce in size at every spur junction point.

The object of the auxiliary joint method is that having connected the permanent pairs from the MDF to DP through a permanent joint, a proportion of the pairs are connected via an auxiliary joint where any alterations in requirements can be made subsequently.  Changes in the growth pattern meant that most changes were made in the permanent joint or between the MDF and the DP and not in the auxiliary joint as expected. 

In certain instances floor standing cast iron cabinets were used and these were square in shape and called Service Cabinets.  These are shown in the pictures below.

      

With the use of the telephone rapidly expanding, from 1945 onwards a new method of distribution was adopted that was flexible and able to cope with growth.  Cabinets were introduced and were generally the first cross connection point from the exchange.  They could be used to feed Pillars which in turn would feed the Distribution Points (DP), but could also feed Distribution Points directly.  A DP was the final connection to the underground cable and can be found at pole tops, on walls and in customers premises.

The Cabinets were called the "Cabinet, Cross Connection" and consisted of the following range:-
Cabinet, Cross Connection No. 1 - Accepted a maximum of 4 terminal assemblies (PC/100).
Cabinet, Cross Connection No. 2 - Accepted a maximum of 6 terminal assemblies (PC/100).
Cabinet, Cross Connection No. 3 - Accepted a maximum of 8 terminal assemblies (PC/100).

The cabinets were and still are painted dark green.

The Cabinets and Pillars afforded flexibility in the network as any incoming wire could be connected to any outgoing wire.  The connection made by a piece of twisted two wire called a "jumper wire".  Before the 1970's Cabinet terminations were actually screws which clamped the jumper wire or in the case of a through connection (i.e. wire 10 to wire 10) two metal bridging pins were used (See picture further down page).  If the screws were over tightened the heads would shear off, to prevent damage.  To prevent over tightening of the screws a torque screwdriver (Torquemaster Screwdriver 22oz) was provided for those working in Cabinets and Pillars.

Enclosed type connection Strip Connection strip components

The assemblies were originally called P100, but these were superseded by the PC/100 assembly which was narrower and lighter than the P100.  This allowed more assemblies to be fitted in the Cabinets.

Bridging Pins No. 1 - Used on open type assembly - obsolete.
Bridging Pins No. 2 - Used on all assemblies except PC/100 type - White plastic head.
Bridging Pins No. 4 - Used on PC/100 assemblies - Yellow plastic head.

When jumpering between connections, 12.5lb two wire was used.  This was originally called Wire, Equipment 2711 which was coloured Red and Blue.  Wire Jumper 6541, coloured Yellow and Blue was used later on.

As telephone penetration rose, Pillars were phased out and the Cabinets fed the Distribution Points directly.

Cabinets were painted dark green and made of cast iron. Today they are made of steel.

Cables from the exchange are terminated on the 'E Side' of the terminating strip whilst the outgoing distribution cables were terminated on the 'D Side' of the strip.

The largest Cabinet (No. 3) can take 800 pairs in and out and the largest Pillar, 200 pairs.

Click here for more information on Cabinets.

In the early 1970's the screw style terminal blocks were replaced with plastic formers and the cable wires just pushed through numbered holes and left hanging.  Connection between wires was made compressed crimps, called Connectors, Wire Insulated No. 1 (white coloured) or Connectors, Wire Insulated No. 1A (blue coloured and grease filled (See picture below).  These connectors were crimped with a tool called a Crimpers, Connector, Wire, Insulated No. 1 or  a Pliers, Crimping No. 2, which can be checked by a Gauges, Check 2.1mm.

Click here for more information on Crimps

Two styles of plastic formers were field trailed and were known as the Midland and Yorkshire types.  The Midland formers were fitted horizontally whilst the Yorkshire formers were fitted vertically.  The Yorkshire type was adopted as the standard.

 


Cabinet, Cross Connection No. 2
The centre bar have been removed for clarity
 

Old style open type connection strips
 

Pillar with crimped connections (Yorkshire Area).
The mounting is called a Strips Connection No. 1.
Blue crimps are grease filled whereas white crimps contain no grease.
Note the two terminals close to the base.  This was connected to an exchange line
for engineering use.


Strips Connection No. 1 showing layout and numbering.
Yorkshire style.


Yorkshire style mounting showing wire routing

 

Yorkshire style mountings - close up
The mountings were normally fitted the other way around.
 


Pillar (100 pairs) showing screwed connections
on enclosed type of strip


Cabinet, Cross Connection No. 1
picture taken in 1949


Close up of screw type blocks in a Cabinet, Cross Connection No. 2 with enclosed strips.
The white dots are the through connection pins.
Picture dated 1949


Cabinet, Cross Connection No. 2


Cabinet, Cross Connection No.3 with local footway joint box open to show cable joints. 
The cabinet is immaculate and has probably just been installed.
The oblong units on the door are metal cases with desiccant in them.  There is a small window in
the middle of the box to see when to change them, as the desiccant goes pink when saturated
with water (they would then be dried out in an oven).  They were used to stop the cabinets
from getting damp inside.
Picture dated 1949

 

Midland Region layout in a Cabinet, Cross Connection No. 1 (single door).
The strips were parallel and they originally used white crimps to connect the wires.
The white crimps were later replaced by grease filled crimps, coloured blue.
The dial at the bottom of the picture is a cable air pressure gauge.
Main cables between the cabinet and exchange were pressured by dry air to prevent ingress by water.
An alarm went off in the exchange if the pressure dropped beyond a pre-defined pressure.
The Yorkshire area also tested an upright assembly, made of clear plastic, which was adopted as the standard.

 

Crimpers, Connector, Wire, Insulated No. 1 - tool used with Connectors, Wire, Insulated No. 1
See picture above

 

Later Cabinet, Cross Connection No. 1
These were made of fibre glass and should be dark green
This one is well faded

 

Cabinet, Cross Connection No. 3
Fibre Glass model

 

Cabinet, Cross Connection No. 3

 


Box Building team installing a new Cabinet No. 3 in place of a Cabinet No. 1

 

New cabinet ready to be lifted into position.
 

New cabinet being lifted into position.
Note the existing connection strips tied together as a temporary measure.

 

 

 
BACK Home page BT/GPO Telephones Search the Site Glossary of Telecom Terminology Quick Find All Telephone Systems

Last revised: January 11, 2024

FM2