PABX No. 7

Extension users guide (PDF)

TELECOMMUNICATIONS INSTRUCTION
C MARKETING
3 Internal
F1070
ISSUE 4 - DEC 1974

This instruction describes the facilities offered by, and the equipment used for the PABX 7. The planning of a PABX 7 installation is dealt with in F1071 and installation instructions are given in F1072.

DESCRIPTION
The switching equipment consists of 4000 type two-motion selectors and Type 2 Uniselectors. The trunking arrangements, which are shown on Dgm SA 8540, are essentially similar to those of the PABX 1. The equipment is accommodated in two cabinets, known as Equipment's, PABX 7/1 .... and 7/2.... having capacities of 9 + 50 and 11 + 50 respectively these cannot be extended. The Equipment, PABX 7/1 .... which includes the ringing and tone supplies can itself form a complete PABX but generally the PABX 7 will be supplied only to those subscribers requiring both units. Both equipment cabinets have doors back and front for engineering access. Power is supplied by secondary cells float charged by a rectifier from the mains supply, this is of the type described in Q0070. The layout of the equipment is shown on Drgs CD 2289 and CD 2290. Relay- sets of types not shown on the drawings are fitted in any of the positions allocated to miscellaneous circuits shelf jacks and the necessary wiring is provided on site when required. A single desk-mounted cordless switchboard, known as Switchboard SA 8551 (see picture) is provided with a handset as standard, but a lightweight headset (trimphone style) can be supplied as an alternative. The normal capacity of the PABX is reduced by one exchange line and one automatic extension line for each auto-auto inter-PBX line or manual extension provided, and by one exchange line for each manual-manual inter-PBX line provided.

NUMBERING SCHEME
The PABX 7 numbering scheme is as follows:-

0 - Assistance
9 - Direct access to exchange lines
8 - Night service
7 -
6 - Direct access to inter PBX routes
5 -
4 - Spare
3 - Spare
200 - 299 Auto extensions
1 - Spare

FACILITIES
The following general facilities are provided as standard and a more detailed description is given in the relevant diagram notes.
Exchange lines Service to the public exchange is given over bothway lines. The PABX calling condition is an earth on the B wire. Enquiry and transfer facilities are available on all exchange calls. Exchange line relay-sets are suitable for connection to CB and automatic public exchanges. To operate to a CBS public exchange a Unit, Auxiliary Apparatus, CBS 536 must be fitted at the public exchange in each PABX exchange line, and Relay-sets SA 8541 at the PABX modified as detailed in F1071, par 23. Requests for connection to other types of exchange should be referred to THQ/TD7.2.2.

Extension lines Extension line circuits are contained in jack-in relay-sets with ten circuits per base. Individual extensions may be barred direct access to the public exchange or completely barred from connection to the exchange. The normal extension signalling limit may be increased by the provision of long line equipment to Dgm SA 8104. Manual extensions with individual appearances on the switchboard may be provided. Incoming service to manual extensions is automatic and under night service conditions automatic outgoing service is provided.

Inter-PBX lines
Terminations for the following methods for signalling are available and are fitted in place of exchange line relay-sets:-

Auto-auto loop dialling (Relay-set SA 8550).

Manual-manual generator AC or BALANCED BATT bothway signalling (Relay set SA 8568)
Provision is not made for the extension of incoming exchange calls to the above inter-PBX circuits. The operator is unable to extend dialled-in 0-level calls which are answered via the assistance circuit and connect extensions to auto-auto circuits. Enquiry and transfer facilities are available on manual-manual but not auto-auto calls.

SCDC
Until such time as full facility SCDC circuits are developed an auto-auto/SCDC converter can be provided. Auto-Auto traffic and facility limitations apply see P1062.

Auto-auto or auto-manual IVF Signalling (SSAC]3) (Relay-sets 1A1/SA 10009)
It is necessary to provide Equipment Signalling No. 24/... when SSAC13 signalling is used.

Auxiliary inter-PBX lines
Auxiliary inter-PBX circuits using Relaysets SA 8109 may be associated with any extension line. This facility is only available where the distant installation is suitable for earth signalling and dialling. Incoming exchange line calls may be extended to auxiliary inter-PBX circuits.

Inter-PBX traffic limitations
Connecting circuits are held for the duration of dialled-in inter-PBX calls and calls from extensions to auxiliary inter-PBX circuits connected to the extension multiple. As inter-PBX circuits usually carry heavier traffic than an extension line the total number of auto-auto and auxiliary inter-PBX circuits should normally be restricted to two per unit. This number may, however, be increased when it is known that the inter-PBX circuits will not be heavily loaded. The GM (Traffic Divn) should be consulted when necessary. This does not apply to IVF SSAC13 circuits.

Night service
Provision is made for level 8 night service at all installations. DC calling devices should be fitted in locations to meet the subscriber's requirements and will normally be Bells 56C. Other types of trembler bell may be used, if required, subject to the current in the circuit from the PABX equipment not exceeding 300 ma with all bell armatures held unoperated. If bells requiring a higher current or mains-driven bells are requested they should be connected as detailed in M0060.

Direct extension night service, and designated extension night service to one extension only, may also be provided when required. These forms of night service may be associated with any extension line. Designated extn night service may be provided in addition to level 8 night service. Both methods allow normal extension facilities during night service.

Introduced in 1969.

Last revised: 30/11/04

FM