GEC C.B. TELEPHONE SWITCHBOARD
FLOOR PATTERN (WITH INDICATOR SIGNALLING)
CS3300 series (Standard) & CS3400 series (Tropical)
16 - 22V DC
When fully equipped, this switchboard accommodates 10 lines for working into any
automatic or C.B. exchange and 50 extensions. The switchboard is fitted
with a dial and dialling keys when ordered. The wiring is in any case
provided to allow them to be added easily if the main exchange is converted to
Extension line indicators are totally-enclosed disc pattern, self-restored
junction lines have hand-restored drop indicators. Negative supervision is
provided by both calling and answering indicators. Corresponding to the
line indicators on the front panel are the line jacks, through which calls are
set up by calling and answering cords. The normal equipment
of the board is for twelve cord circuits, but fifteen cord Circuits are wired
and can be equipped to order any pair of lines may be connected by any pair of
cords. RING keys and SPEAK keys enable the operator to ring any wanted
line and speak over any selected cord circuit.
The operator is provided with a telephone handset, mounted on the side of the
cabinet when not in use a headset may be supplied instead.
The key shelf is hinged. The apparatus and wiring are
readily accessible by a lift-out door at the back of the cabinet.
Features Common to all Central Battery
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
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.
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.
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.
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
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 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.
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.
Switchboards are supplied with an operatorís handset or headset telephone as
required. The circuit of the operatorís telephone has great transmitting and
receiving efficiency with full sidetone suppression.
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.
The switchboards may be supplied with a tropical finish to combat the
effects of tropical climates.
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.
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:-
|SIZE OF COPPER CONDUCTORS
||MAXIMUM PERMISSIBLE LENGTH
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
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
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
||No. of Lines
||55.25 x 24 x 26
||140 x 61 x 66
Taken from the GEC Publication No. CSL. 8