|PRIVATE AUTOMATIC EXCHANGES
Extensible Unit Type
Being of extensible type, this register-controlled PAX is ideal for progressive organisations where expansion from time to time may be anticipated. It employs single-motion selectors throughout and may be partially or fully equipped up to a maximum of 400 lines, the minimum number of lines being 50. The exchange equipment is composed of 50-line units specially designed to facilitate extension, an open-type main distribution frame (accommodating fuses and arrestors, if required) and the power plant. Maximum extension-line loop resistance, including the telephone, is 1000, but long-line equipment to extend this limit can be supplied.
PAX 50/400 stock units, with some apparatus covers and the front doors removed are shown on the right. Note cable support on top.
Numbering and Facilities
Preference ('automatic' or 'optional'). Enables selected extensions to switch in on engaged lines. One resistor per preference line is required for fitment on the unit. For automatic preference, one PF relay per register is also required. With optional preference, access to an engaged line is obtained by dialling a further digit.
Tie Line. For intercommunication between two PAXS. Suitable terminating equipment is necessary at the remote PAX, therefore the type of exchange should be specified. Extra equipment is necessary for long lines. Preference extensions can be given access to a busy tie-line and to a busy extension at the remote PAX if required.
Loudspeaker with Direct Call. Executive's loudspeaker telephone equipped with 10 keys for the direct calling of up to 20 selected extensions by a discriminated ringing signal.
Conference and Direct Call. Direct-call keys referred to in the previous paragraph can be used to connect together the executive and up to 10 direct-call extensions for conference when the conference facility is specified. Direct-call facilities do not necessarily include conference.
Secretarial. For the executive who may not wish to be always directly accessible by telephone. Various schemes available.
Two-Party Lines. Permits individual service to two extensions over one pair of wires. The two can communicate with each other, and either can make or receive calls without disturbing the other. Three numbers are allocated per two-party line.
Loud - Ringing Bells. A loud - ringing mains signalling bell, such as N3137B, can be operated via the contacts of a d.c. relay supplied in a case.
Staff Call. Selected persons may be called by dialling a code number to operate bells or buzzers throughout the premises. A person thus called dials 8 on the nearest telephone and is automatically connected to the caller. There are various visual schemes for up to 64 codes, or audible schemes, or schemes giving a combination of both audible and visual signals. Details on request. All signalling devices should be ordered separately.
Discriminating Ringing. For use b executives or other selected extensions to indicate when such persons are calling.
PBX Hunting. Enables a number of lines (usually up to 4) to be called by dialling the first line directory number. If the first line is engaged, the call is automatically connected
to the second line, and so on. If the directory number of the second or third line is dialled, the call is not connected to the next line under engaged conditions.
Emergency Lines. Where lines are used as reporting points for emergency calls, such as fire alarm, ambulance, etc., normal line circuits would be terminated on tele- phones (usually red) not equipped with a dial, to prevent them being used for outgoing calls. If it is required that these extensions be called by dialling a number outside the normal numbering scheme, additional equipment is necessary.
Units may be type 'A' or 'B', equipped to order and are installed in suites in the sequence: A.B.B.A.B.B.A.B. in order to simplify extension, all are fully wired and the maximum number of wire connections are completed in the factory. All switches are heavy-duty (BPO No. 2) uniselectors.
Line relays are twin type N44700; other relays are N30000 (BPO 3000) type.
Inter-unit cables are run through the sides of the cabinets whilst i.d.f. cables are on supports attached to the top. Both sets of cables are soldered to connection strips.
Main Distribution Frame
A unit N22475
Last revised: October 07, 2019