GEC C.B. PMBX

GEC C.B. TELEPHONE SWITCHBOARD
CORDLESS TABLE PATTERN WITH LAMP SIGNALLING
CS5100  series (Standard) & CS5200 SERIES  (Tropical)

16 - 24V DC
This switchboard, with its highly polished cabinet of walnut veneer and its attractive design, is a decorative asset to its surroundings.  It is especially suitable for use on a reception desk, for instance, where it may be seen by all visitors. As the operator's telephone is not normally supplied with the cabinet, any instrument may be ordered that is in keeping with the surroundings.  The CS5105 (4+10) model is show pictures to the right and in additional pictures, at the bottom of this page.

The capacity of the board ranges from one junction line (to any automatic or C.B. exchange), with three extensions to five junction lines and twenty extensions.  Each line is indicated by a numbered lamp signal. Keys under each line lamp enable the calling line to be connected to any one of the connecting circuits, of which the largest size board has seven.  The operator speaks over the selected link by using the SPEAK key associated with it, and sets up a call by connecting the wanted line to the same link circuit, operating the RING key and then turning the handle of the ringing generator. Positive supervision is provided on all calls.

The back of the cabinet can be removed to give access to the wiring, and apparatus which is mounted on a chassis in the cabinet.  The chassis may be withdrawn without disturbing any wiring.
 

Features Common to all Central Battery Switchboards

FACILITIES
Each of these switchboards permits its operator to set up calls between its extensions. Provision is also made on the switchboard for one or more junction lines to the public exchange. When these junction lines are equipped, the operator can set up calls between the switchboard extensions and the public telephone system.

To almost all the switchboards keys are fitted which, in the absence of the operator, connect the exchange lines directly to any selected extensions. These extensions may then be used exactly as if by an ordinary subscriber on the public exchange, provided the instruments are fitted with dials or ringing generators if the public exchange is automatic or magneto.

All boards are provided with a buzzer which, if switched into circuit, gives audible indication of incoming calls.

CONSTRUCTION
Cat. No. CS5100/5200 series switchboards have a highly polished walnut veneer cabinet. The other boards described are housed in matt polished hardwood. All cabinets are sturdy in construction and allow easy access to the wiring and apparatus they contain.

CAPACITY
All switchboards in the range are fully wired for the maximum number of lines quoted, but can be supplied only partially equipped so that both immediate needs and future additions are catered for with the greatest economy.

SIMULTANEOUS TRAFFIC
The number of calls that may be passed through the switchboard simultaneously is determined by the number of cord circuits or connecting circuits with which the switch board is equipped.  This number is quoted in the specification tables given in this Catalogue for every size in each range of switchboard.

POWER SUPPLY
Power for operating the switchboards may be obtained over power leads from the main exchange.  Alternatively, power may be drawn either from AC mains via a mains unit or from a local battery, preferably float-charged, which need have no more than a 10 ampere-hour capacity.

RINGING GENERATOR
Ringing current is normally drawn from the compact and powerful hand generator, but on cord switchboards provision is made for the connexion of an external source of ringing current, such as ringing leads from the main exchange, a local vibrator, or a ringing machine, to facilitate operation.  The hand generator then acts as a standby.

SUPERVISION
Lamps or indicators inform the operator when a call is pending, is in progress, or has been completed.  Positive supervision is said to be provided when the replacing of a handset at the end of a call lights a lamp or operates an indicator negative supervision, when the replacing of a handset extinguishes a lamp or restores an indicator.

OPERATOR'S TELEPHONE
Switchboards are supplied with an operator's handset or headset telephone as required.  The circuit of the operator's telephone has great transmitting and receiving efficiency with full sidetone suppression.

CORDS
G.E.C. switchboard cords are of great durability.  The tinsel used in them is tested to ensure a life of 200,000 reciprocations without conductor fracture.

FINISH
The switchboards may be supplied with a tropical finish to combat the effects of tropical climates.

TELEPHONE INSTRUMENTS
The instruments recommended for extensions are the Gecophone, the G.E.C. Table Telephone, and the Muraphone, described in Catalogue Leaflets STL 9, 10 and 12 respectively.  Extension instruments requiring the facility of dialling direct into an automatic public exchange, when connected at the switchboard to the junction lines, should be fitted with dials.

LINE WIRES
Each extension requires a two-wire connexion to the switchboard.  Any adequately insulated twisted pair, suitably protected if exposed to the risk of damp or of mechanical damage, may be used, provided the line loop resistance does not exceed:-
200 ohms for switchboards without line relays.
600 ohms for switchboards containing line relays.

The following table gives examples of maximum lengths of line wires:-

The line loop resistance is the resistance of both wires of a pair in series.

DISTRIBUTION, CABLING AND PROTECTION
The simplest method of connecting extension instruments to the switchboard is to run the line wires of each instrument directly to the terminal strip within the switchboard.  Economy in line wires may often be effected by running a multi-core cable from the switchboard to a junction-box, so situated that only a short length of line wires is then needed to connect the instrument to the junction-box.

A distribution frame often simplifies the distribution scheme, particularly with a switchboard of large capacity.  The wires from the switchboard, which are usually run in a multi-core cable, are terminated on the distribution frame to which the extension instruments are then wired.  The use of a distribution frame simplifies alterations to numbering, line testing and the connexion of additional lines, and also provides protection against any high voltage and heavy currents that may accidentally be introduced from extraneous local sources.

PROTECTION
In installations without distribution frames, line wires run outside the building should be protected against lightning by protection apparatus that is supplied if ordered.

 
Catalogue Numbers and Specification Table

 Taken from the GEC Publication No. CSL. 8

ADDITIONAL PICTURES

CS5101 (pictured 1954)
 

CS5101 rear view with back removed (pictured 1954)
 

CS5101 rear view with chassis partly removed (pictured 1954)
 

CS5101 with chassis removed (pictured 1954)

CS5102 (pictured 1954)
 

CS5102 rear view with back removed (pictured 1954)
 

CS5102 rear view with chassis partly removed (pictured 1954)
 

CS5102 with chassis removed (pictured 1954)
 

CS5104 (pictured 1951)
 

CS5104 rear view with back removed (pictured 1951)
 

CS5105 (pictured 1950)
 

CS5105 rear view with back removed (pictured 1950)
 

CS5105 chassis removed from case (pictured 1950)

Last revised: November 25, 2021