private automatic branch exchange
3 public-exchange lines.
10 extension lines.
Provision for 2 simultaneous inter-extension calls in addition to a maximum of 3
00 to 09 for extensions; single digit other than 0 for tie lines.
Public exchange service
direct access from extensions after operating a pushbutton switch on the
telephone. Individual extensions
can be prevented from dialling public-exchange calls.
No operator's switchboard is required; a call is answered at one of up to 4
designated extensions and routed to the required extension by the enquiry and
transfer method. The call can be
offered to an extension already engaged.
Enquiry and transfer
Telephones with a pushbutton can be supplied* to all or selected extensions to
enable a public exchange call to be held while the user calls another extension
with an enquiry. When the enquiry
is complete, the original extension
returns to the public-exchange call, or can transfer it
to another extension.
Selected executives can break into an existing conversation by dialling an extra
Mains fail protection
Public-exchange lines can be connected automatically to designated extensions in
the event of an AC mains supply failure.
1 or 2 on one route only.
Designated extensions can be connected together via a special circuit.
Staff absent from their offices may be called by dialling a special locating
number and a personal code, to operate lamps or bells.
A secretarial switching telephone enables secretaries to filter calls to an
Individual extensions may be permitted to dial local but not long-distance
Mode of operation
Fully automatic operation using uniselectors and relays.
All conversations secret from each other.
Tones and ringing
Mains-supply derived dial tone, ringing tone, ringing current and executive
intrusion tone; electronically derived busy, number-unobtainable and link throw
off tones. When the exchange
operates from a battery power supply, all tones and ringing current are provided
by an all-electronic tone generator.
Required dial-pulse characteristics: 7 to 14 i.p.s., 2:1 break to make ratio.
Audible indication of blown fuse.
Built-in AC power unit: Input, 100 to 120V or 200 to 250V 50 to 60 Hz single
External Battery: 50V 32 AH ; with float charger, input as for AC power unit,
output 50V d.c 3 A.
Line loop resistance
Not to exceed 1000 ohms.
Wired-in units on a steel framework in a floor-mounting steel cabinet
(painted dark green) with lift-off dust-proof panels front and rear.
Dimensions and weight
Switching equipment PB2202
151cm (60 in)
75cm (30 in)
39cm (16 in)
175 kg (385 lb)
Float charger SU4202
53 cm (21 in)
39 cm (15 in)
24 cm (9 in)
35 kg (76 lb)
*To be specified when ordering
GEC-AEI TELECOMMUNICATIONS LIMITED
A Management Company of The General Electric Company Limited of England
3 + 10 LINE PRIVATE AUTOMATIC BRANCH EXCHANGE
The G.E.C. 3 + 10 line private automatic branch exchange has a capacity for
three lines to a public exchange and ten extensions. It has no switchboard or
attendant. One extension calls another by dialling two digits. An extension
obtains direct access to the public exchange (either automatic or C.B. manual)
by depressing a pushbutton on the telephone instrument. This direct access is
given to selected extensions and withheld - if desired from others.
An incoming call from the public exchange is answered by any of four
pre-determined extensions, who may then transfer the call to the wanted party. Up to two extension-to-extension conversations can be held simultaneously. When
an extension makes a call to the public exchange, the connecting link in the
PABX is not used. Thus, calls can be made to the public exchange even when both
links are in use.
The PABX is mounted in a sheet-steel dust-proof cabinet having lift-off doors
front and rear to give access to the equipment. The size of the cabinet is 4'
11" x 2' 5" x 1' 4" (150.7 x 75 x 39.4 cms). When required, the equipment
can be supplied as a free-standing open rack without the cabinet. The dimensions
are then 4' 6" x 2' 5" x 1' 6" (137.4 x 74.3 x 45.7 cms). The exchange
employs the same apparatus as has been standardised for large public exchanges
by many Overseas Governments and the British Post Office.
||Rear View (Less cabinet)
Any extension user is connected to any other extension by dialling the
appropriate number. The extensions are numbered from 00 to 09.
Direct access to the public exchange is obtained by depressing the pushbutton on
the telephone instrument. If the public exchange is automatic, the caller then
dials the number of the required subscriber; if the exchange is manual, the call
is completed by the public-exchange operator. Certain extensions may be barred
from this facility, if desired, by a simple adjustment to the strapping in the
Equipment can be supplied to prevent certain extensions having direct access to
the public exchange dialling their own trunk calls, (see Additional Features).
A call from the public exchange is taken by any one of four Answering
Extensions, who are pre-determined and can transfer the call to any extension by
depressing a pushbutton on their telephone and dialling the wanted number. If
required an extension can be prevented from receiving an exchange call by a
simple adjustment to the strapping. Should an Answering Extension attempt to
transfer an exchange call to an extension that is barred these calls, the
Answering Extension itself will be re-rung. An incoming call is signalled on
separate bells, which are located at points convenient to the Answering
Extensions. These bells are additional to those incorporated in the telephone
instruments. If both link circuits are engaged when an Answering Extension
attempts to transfer a call he can interrupt one of the conversations by holding
the pushbutton depressed for an extended period. This causes a warning tone to
be sent to the two conversing extensions who should then restore their handset. If they do not, the link is force released after a short interval to allow the
main exchange call to be connected. Should busy tone be received after the
wanted number has been dialled, then the Answering Extension dials 1 to
interrupt the established call.
CALL-BACK AND AUTOMATIC TRANSFER
An extension engaged on a call over an exchange line may hold the call (by
depressing the pushbutton on his telephone), whilst he calls any other
extension. At the end of conversation with the second extension, he resumes his
conversation on the exchange line by depressing the pushbutton again. Alternatively, if he wishes, he may transfer the exchange line to the other
extension merely by replacing his own handset, provided the second extension is
allowed to receive transferred calls. A call may be re-transferred as often as
required between extensions.
EXECUTIVE RIGHT-OF-WAY (PRIORITY)
An Executive may break in should the extension he requires be already engaged. When he hears busy tone, he dials a further digit
'1' to interrupt the
Two methods of operation are possible, private and non-private, the required one
being selected by a simple adjustment to the strapping in the automatic unit.
When the `private' operation is used, an intrusion tone is heard by both
parties, but the executive who wishes to contact one of them cannot hear the
conversation in progress. Upon hearing the intrusion tone both parties should
replace their handsets, whereupon the required extension will be rung without
any further operation by the executive.
When the `non-private' operation is used, an intrusion tone is heard by both
parties and the executive can immediately enter the conversation. He can, in
fact, carry out the whole of his required conversation without the original call
being cleared. However, if the executive expects to carry on a long conversation
it is advisable that the original call is cleared; the wanted extension will
then be called automatically as described above.
Night service is provided by arranging for one or more of the Answering
Extensions to answer incoming calls at night.
MAINS SUPPLY FAILURE
Should the mains supply be interrupted, operation of the PABX ceases when it is
operated from a mains supply unit, but the result is not isolation from the
public system because the three exchange lines become automatically connected to
any three extensions, from which calls on the public system may be made or
RINGING AND TONES
When the exchange power supply is obtained from the mains rectifier unit, dial
and ringing tones, together with ringing current, are derived from the mains
unit and busy tone from a vibrator relay.
Should a fuse in the exchange unit blow, an audible alarm
signal is given.
The standard PABX is wired to allow several additional features to be provided
either at the time of installation or at a later date. The apparatus
required to provide these additional features is mounted external to the main
automatic unit. The additional features include:-
Up to two tie lines can be provided between the PABX and another private
telephone exchange, either in an adjacent building or in a building several
miles away, to permit intercommunication between extensions in both buildings.
Please state the type of private exchange into which the tie lines must work and
the line-loop resistance of the tie lines themselves. Should an existing
exchange be of other than G.E.C. manufacture, its circuit drawings should be
provided with an enquiry.
Officials absent from their offices can be called by a system of lamps or bells. A special `locating' number is dialled, from any telephone followed by the
digits in a personal code. Please state whether a visible or audible call is
required, how many codes are needed, and the number of calling stations likely
to be used.
These enable conferences to take place by telephone while the participants
remain at their desks. The conference is opened by each participant being
individually called by the convener; each then dials a special digit to gain
access to the conference circuit. Immediately the
connexion is established, the link circuit is released. No extra line wires or
pushbuttons are required. The executive right-of-way facility cannot be used to
gain connexion to an extension engaged on a conference call. In these
circumstances the executive hears a special tone to indicate that the extension
is in conference. Please state the number of participants required.
If necessary, additional equipment can be supplied to prevent those extensions
having direct access to the public exchange from dialling their own trunk calls. Please give details of those digits and combinations of digits that are to be
A secretary may be provided with a G.E.C. Switching Telephone so that all calls
to an executive may be filtered. The executive would have a G.E.C. Extension
Telephone. Calls between the executive and secretary are not routed through the
PABX. This service is fully described in Catalogue Leaflet STLI7.
OTHER PUBLIC EXCHANGES
When the public exchange is other than an automatic or C.B. Manual type, e.g.
magneto or C.B.S., a n auxiliary unit is required to effect the necessary
signalling. Please state the type of public exchange.
BATTERY POWER SUPPLY
Should the mains supply be unreliable, a storage battery and float charger
can be supplied to ensure continuity of service. This replaces the
built-in power unit. In addition,
a ringing vibrator must be fitted to supply the ringing current and tones etc.
Similarly, should the mains supply be DC the exchange must be operated from batteries with a rheostat to step the
mains voltage down to the value required to charge the batteries. With this
arrangement a charge-discharge system must be used
so that the battery connected to the mains is isolated from the exchange.
Any automatic telephone having a dial speed of between 7 and 14 pulses per
second, with a ratio of 2 to 1 break to make, is suitable for use with this
Recommended telephones are the `G.E.C. 1000' Telephone, the Muraphone `K' and
the New Gecophone described in G.E.C. leaflets STL13 and STL16.
A telephone fitted with a pushbutton is supplied for each of the Answering
Extensions and for any other extension requiring the call-back and automatic
transfer facility. When ordering, please state the number of telephones required
with pushbutton fitted.
G.E.C. Loudspeaking Telephones, which enable the user complete freedom of
movement about the office whilst making a call, are fully described in Catalogue
Leaflet No. STL15.
Any insulated twin conductor, suitably protected if exposed to risk of damp or
mechanical damage, may be used to connect the telephone to the exchange,
provided the line-loop resistance does not exceed 1000 ohms.
|Size of Copper Conductors
||Maximum Permissible Length of
||AWG (B & S)
DISTRIBUTION AND PROTECTION
The simplest method of connecting the extension instrument to the PABX unit is
to use separate line wires for each telephone. A saving in line wires and space,
with a gain in neatness, may often be effected by running a multi-core cable
from the PABX unit to a distribution box so situated that only short lengths of
line wires are required to connect each telephone instrument to the distribution
The exchange equipment must be protected against high voltages and heavy
currents, which may accidentally be introduced into external lines from
extraneous sources. Both the lines to the
public exchange and all external extension lines must be connected to protection
apparatus before being extended to the exchange unit. For this purpose the
G.E.C. protector, Cat. No. PR1111, containing fuses and electrodes is
recommended. Protectors for the exchange lines are often supplied by the public
telephone exchange Administration.
On receipt of a dimensional sketch of the premises, with indication of the
location of each telephone, the most economical distribution scheme will be
planned and quotations for material submitted.
G.E.C. 3+10 LINE P.A.B.X.
||59 x 29 x 15
||150.7 x 75 x 39.4
For normal use a power unit is built into the exchange. This operates
from a 100/120 or 200/250-volt 50/60 c/s single-phase mains supply. Where
a battery and float charger are required the following are recommended:-
Automatic Float Battery Charger for operation from a 100/120 or 200/250 volt
single-phase mains supply having an output
of 48/52 volts, 0-3 amp DC, and suitable for
charging a 24-cell lead acid battery.
Dimensions: 21 x l5 x 9.5ins; 53 x
39 x 24cms
Weight: 761b; 34.6kgs
Catalogue Number: SU 4202
24-Cell Lead-Acid Storage Battery less stand, acid and accessories, capacity 20
ampere hours at 10-hour rate of discharge.
Catalogue Number: BA 1103
Taken from the GEC Catalogue Leaflet No. PXL 08 (Date unknown but later than
also GPO PABX 5
|Without cabinet - Drawing 701721 - Front view
||Without cabinet - Drawing 701721 - Rear view
|With cabinet - doors removed
||With Cabinet - doors and some covers removed