plessey1.jpg (6468 bytes)PLESSEY
PABX PB 8000

Private Automatic Branch Exchanges

pb8000.jpg (28918 bytes)The PB8000 is an extensible register-controlled exchange intended to serve medium-to-large organisations. With minor variations it caters for 100 to 8000 extensions and provides the latest facilities, including press button signalling and 'cordless' operation of its manual switchboards. Depending on the size and traffic requirements, the PABX employs a four or five-stage switch network based on the proven Plessey 5005 crossbar switch. The exchange has a high traffic-handling capability of 0.2 erlang bothway traffic per extension. No limit is imposed on the number of exchange or inter-PBX lines required.

Design Highlights
Full press button operation.

High quality speech/data transmission. Flexible numbering.

Attractive equipment units.

Easy-to-operate switchboard consoles.

Switchboards: single, back-to-back or 'en suite' installation.

Low maintenance.

Simplified installation.

Extension Classifications
Extensions can be arranged in any of five service classifications by appropriate wiring straps.

Unrestricted - Full traffic facilities within the national network.

Preference (or Priority) - Full traffic facilities including Direct International Subscriber Dialling (DISD) and intrusion into established extension-to-extension calls.

Trunk barred - Direct-access external calls limited to 'local-fee' areas.

Barred direct access - External calls originated and received via the PABX switchboard only.

Fully barred - Internal calls only.

Extension Facilities
Extension-to-extension calls are unrestricted and connected automatically when keyed by the calling extension.

Assistance calls to the operator.

Inter-PBX calls obtained automatically or via the operator.

Direct access to the public exchange by keying a single digit, e.g. '9'.

Hold for enquiry by pressing the enquiry button once, enabling an extension to hold an established external call while making an enquiry call to another extension. Automatic transfer by the originating extension of an established enquiry call to the called party on handset replacement. If misoperation by the originating extension occurs the external call is automatically transferred to the PABX switchboard.

Operator recall by successive keying of the enquiry and assistance digits. A second operation of the enquiry button returns the extension to the external party.

Through clearing via both automatic equipment and switchboards.

Calling-party release.

Forced release of calling party 20 seconds after release by called party.

Discriminating ringing to differentiate between internal and external calls.

pb8000x.jpg (46092 bytes)
Operator Facilities
Press button signalling.

Selective answering.

Lamp and tone supervision of call progress.

Automatic release of established calls, with optional supervisory hold facility.

Ring-when-free condition applied automatically on calls from the PABX operator to engaged extensions.

Operator intrusion.

Call splitting on external calls, enabling the operator to speak to called or calling parties in secrecy.

Call release by the operator on calls answered at the switchboard but not extended.

Public-exchange-operator recall.

Waiting-calls indicator.

Route-busy indication by illuminated outgoing group button or display of the numerical identity of engaged route.

Numerical-identity display of faulty operator associated circuits.

Audible and visual indication of incoming calls.

Extended prompt/deferred alarms from the automatic equipment.


System Facilities

Register capacity of 18 digits.

Standard ringing and tones.

Standby ringing machine.

Line lockout occurs if a call does not proceed within the permitted time after handset pick-up, or if a caller fails to clear at the end of a call.

Night service enables incoming calls, during the night-service period, to be either routed to selected extensions or to ring special bells and be answered by any extension keying the appropriate digit, e.g. '8'.

Transit switching of inter-PBX calls by connecting an incoming call through the exchange to an outgoing line.

Call-count metering for traffic analysis and maintenance.

Out-of -order or test-and-busy cabinet.

Alarm panel on the automatic equipment gives audible and visual indication of any fault adversely affecting the operation of the exchange equipment.

Line test case with Keyset, meters and indicators, etc., to facilitate the detection of faults on lines and circuits within the PABX.

Register store tester.

Equipment monitor for print-out of switching stages and relay groups involved in equipment failure, together with details of the fault.

Optional Facilities
Group hunting

Dictation recording

Direct-access keycalling

Absent-extension diversion


Switchboard intercommunication

Supervisor's desk

Enquiry desk

Connect-circuit metering

Suite transfer

Calling-extension line identification

Direct dialling-in (DDI)

Emergency services

Satellite working, with PB8000 as main exchange Equipment congestion recording

Traffic recording

Long-line extensions

Staff calling (various systems)

Watchman's patrol

Graduated howler

Data switching

Data transmission and capture Short-code dialling

Automatic call diversion

Traffic analysis

Program control of extension numbering scheme

Call accounting

Absent service

Automatic call back

Group hunting

Program control of class-of service options.

External number repetition


Equipment Practice
The automatic equipment is housed in double-sided racks assembled on site on a wooden plinth secured to the floor for stability. The structural framework is of sheet and angle-section steel, attractively finished in a dual smooth/textured hemp beige and loam brown enamel.

System 2150
pb8000x.jpg (46092 bytes)Plug-in equipment shelves are used throughout to facilitate installation and subsequent extension. The shelves, containing crossbar switches and/or relays, can be swung forwards and downwards to a self-locking position for inspection and testing. Wiring is by solderless gun wrapping, and PVC-insulated wire is used throughout. The equipment is protected front and back by hinged metal doors, and lift-off covers of clear flame-retardant plastic. Each cover is retained in position and dust-sealed by magnetic rubber tape around its periphery, and can be conveniently 'parked' against adjacent covers or framework when required. All inter-rack wiring except the power cabling is routed along the top of the suite and enclosed behind dust-proof covers. Power cabling runs along the bottom of the suite and is connected to fused power-distribution panels at the base of each inter-rack frame.

Dust covers along the base of the suite pivot forward to give access to the fuses.

Operator Switchboards
The switchboards, which match the PABX equipment in colour and finish, can be arranged singly, back-to-back or en suite.

On the face of the switchboard are number displays, meters, press buttons and lamps. For simplified operation and space economy, control press buttons have in-built supervisory lamps and simple press-to-release or non-locking actions. A press button Keyset is provided for rapid handling of calls. 

Switchboard dimension (approx.)
Height 3ft 1 in (0.94m)
Width 2ft 11 in (0.89m)
Depth 2ft 7in (0.79m)

Ringing and Tones
Standard ringing and tones are supplied by a BPO approved dynamotor tone generator. Two different ringing cadences are used to discriminate between extension-originated calls and incoming public-exchange or inter-PBX calls.

The telephones normally used with this PABX are the dc press button type.

Line Limits
Maximum extension-line loop resistance is 1000ft (including the telephone). Exchange-line limits may be up to 1000ft depending on the limits imposed by the remote exchange.

Inter-PBX line limits depend on the type of signalling used and maybe greater than 1000 ft.

The exchange operates from a nominal 50V float-charged negative-battery supply. A single battery caters for current loads of up to 200A; above this limit duplicate battery float plant is provided. A 50V positive supply, derived from dc/dc converters, is also required to cater for press button signalling (CCITT code C).

PUBLICATION No. 7651, 4/76

Home page BT/GPO Telephones Ericsson Telephones Ericsson Home Page Ericsson PABX All Telephone Systems

Last revised: October 10, 2019