HOUSE EXCHANGE SYSTEM (HES)
No's 1 & 2

This system was produced by Ericsson (ETL).

Introduced circa 1935.

TELECOMMUNICATIONS INSTRUCTION
C MARKETING INSTALLATION
3 Internal
C 3020
Issue 1, Dec 1970

HOUSE EXCHANGE SYSTEM No's 1 and 2
Description of Equipment

1. Scope of Instruction
This Instruction describes the various items of equipment used on the House Exchange System.  The terms multiple station, 1+5 system, etc, are defined in C3001.  The installation of the system is described in C3023.

2. Contents
The paragraph dealing with the various items of equipment are as follows:-

Para's 3 to 8 - Telephones.
Para's 9 to 14 - Transfer units.
Para's 15 to 18 - Plugs, cords, jacks.
Para 19 - Junction boxes.
Para's 20 to 25 - Other items.

3. Telephones: Types in Use
The present-day standard intercom. telephones for use on the house exchange system are:-
Telephone, Intercom, No. 1/1 (Mk. 2) for multiple stations on the 1+5 system.
Telephone, Intercom, No. 1/2A (Mk. 2) for multiple stations on the 2+10 system.

Superseded designs of these telephones which may still he issued from Supplies Dept. for new work are:-
Telephone, Intercom, No. 1/1 (Mk. 1) and No. 1/2 (Mk. 1 and Mk. 2).

Earlier patterns which may still he met with on existing installations but which will no longer be issued for new work are:- Telephone, Intercom, Nos. 1 and 2.  These early telephones are not provided with a tray but are otherwise very similar in external appearance to the later models.  The No. 1 type is superseded by the No. 1/1 type and the No. 2 type by No. 1/2 and No. 1/2A types.  Where a hearing-aid amplifier is required at a multiple station on the house exchange system, Telephone, Intercom, No. 1/1B (Mk. 2A) is used for the 1+5 system and Telephone, Intercom, No. 1/2B (Mk. 2A) for the 2+10 system.  These telephones are described in par. 8.

4. Telephone Intercom, No.... (Mk.. 2A)
Future supplies of Telephones, Intercom, Nos. 1/1, 1/2A, 1/1B and 1/2B will be fitted with a new type of handset plunger, designed to reduce the possibility of sticking.  Telephones with the new plungers will be distinguished by the addition of the letter A as a suffix to the mark number, e.g., Telephone, Intercom, No. 1/2A (Mk. 2A).  In all other respects, these telephones will be as described elsewhere in this Instruction for items without the mark number suffix A.

5. Telephone, Intercom, No. 1/1
This telephone is used on installations having one exchange line and five (or exceptionally, six) local stations.  The mechanism is mounted on a metal base, measuring approximately 11in. x 5in., and is enclosed in a black, moulded cover (Cover No. 4) with a cradle rest for the telephone handset (Telephone No. 164).  On the sloping top surface of the telephone is a row of 7 plunger keys comprising, at the top, the exchange-line key (coloured red), followed by 5 black local-call keys and, below these, the conference key marked 'C ' (coloured green).

The operating procedure for the keys is described in Adjacent to the keys is a window under which a paper label bearing station numbers, etc. may be inserted via a slot in the top edge of the sloping key panel.  The labels are described in A3202 and are obtained separately, as required.  The label may be removed by first moving it. forward with the Point of a pin inserted into a small slot provided for the purpose above the window.

The handset of the Telephone, Intercom, No. 1/1 (Mk. 2) has a Receiver, Inset, No. 2P; that of the Mk. 1 telephone has a Receiver, Inset, No. 1L. All new telephones will be Mk. 2 (or Mk. 2A, see par. 4) and will also include a Coil, Induction, No. 27; old telephones of either Mark Number may contain an earlier pattern induction coil, such as the Coil, Induction, No. 22.  As issued from Supplies Dept, each telephone is fitted with a dummy dial which, in automatic areas, may be replaced locally as required by the appropriate Dial, Auto. S.S.No.10....

A Holder and Tray No. 2 is fitted under the base of the telephone and the complete telephone includes a desk cord (6 feet long) terminated on a plug fitted with a buzzer. For use at a main station, internal strapping points are provided in the telephone to enable exchange-line monitoring or trunk - offering facilities to he given.  The use of these straps is described in C3023.  The circuit of the telephone is shown on Diagram Q(L) 131 and the wiring on Diagram Q(L) 141.  The complete telephone weighs approximately 9.5lbs.

6. Telephone, Intercom, No. 1/2A
This telephone is used on installations with two exchange lines and ten (or exceptionally, eleven) local stations.  The mechanism is mounted on a metal base and is housed in a moulded cover of the same type and dimensions as for the Telephone, Intercom, No. 1/1.  The telephone is similarly fitted with a tray and dummy dial and includes a desk cord (6 feet long) with plug and buzzer.  The handset of the Telephone, Intercom, No. 1/2A (Mk. 2) has a Receiver, Inset, No. 2P; that of the Mk. 1 telephone a Receiver, Inset, No. 1L.  The Mk. 2 telephone also includes three resistors not fitted in the Mk. 1 type; the function of the resistors is described in C3022.

All new telephones will be Mk. 2 (or Mk. 2A, see par. 4) and will include a Coil, Induction, No. 27; old telephones of either Mk. No. may contain earlier-pattern induction coils, such as the Coil, Induction, No. 22.  Telephone, Intercom, No. 1/2A has 13 plunger keys, comprising two exchange-line keys (coloured red and numbered 1 and 2) placed one above each of two rows of 5 black 'local' keys, with the conference key marked 'C' (coloured green) placed centrally below the others.  Immediately above and associated with each exchange-line key is a trigger key (coloured red), the functions of which are described in Q1003.  A window for a 'local' station designation label is provided adjacent to each row of keys.  In addition to internal strapping points to give exchange-line monitoring or trunk-offering, the telephone has strapping points for use when it is fitted on a main station to enable a local station to call the main when it is engaged on an exchange call.  The use of these straps is described in C3023.  The circuit of the telephone is shown on Diagram Q(L) 231 and the wiring on Diagram Q(L) 241.  The complete telephone weighs approximately 10lb.

7. Telephone, Intercom, No. 1/2
The external appearance of this telephone is identical to that of the Telephone, Intercom, No. 1/2A.  The internal construction and circuits of the two telephones are also very similar but a Telephone, Intercom, No. 1/2 cannot be used at a main station which is required to be called locally while engaged on exchange calls, because the necessary strapping points are not provided in the telephone.  The circuit of this telephone is shown on Diagram Q(L) 231 and the wiring on Diagram Q(L) 241.  The handset of the Telephone, Intercom., No. 1/2 (Mk. 2) has a Receiver, Inset, No. 2P and the Mk. 1 pattern had a Receiver, Inset, No. 1L.  Early versions of this telephone may be fitted with a Coil, Induction, No. 22 (Mk. 1), but those of later construction include a Coil, Induction, No. 22 (Mk. 2) [see Diagram Q(L) 231].

8. Telephones, Intercom, No. 1/1B (Mk. 2) and No. 1/2B (Mk. 2)
These telephones are used with the hearing-aid amplifier, Repeater, Telephonic, No. 17C, and are normally produced from the Telephone, Intercom, No. 1/1 and No. 1/2A (Mk. 2), respectively, by the addition of a, Potentiometer No. 8B and a subsidiary terminal strip for connection to the repeater.  The control knob of the potentiometer projects through a slot cut in the side of the telephone cover.  The circuits of the telephones are shown on Diagram Q(L) 134 and Q(L) 235, respectively and the wiring on Diagrams Q(L) 144 and Q(L) 244, respectively.  Diagram Q(L) 158 shows the method of connecting the telephone to the repeater.

9. Transfer Units.
The present-day standard types of transfer unit for use on the house exchange system are:-

Unit, Transfer, Intercom, No. 1 (Mk. 2) for use at 1st and 2nd choice main stations on installations with one exchange line and without a non-multiple station and at a 2nd choice main station on installations having one exchange line and a non- multiple station. See also under Unit, Transfer, Intercom., No. 3.

Unit, Transfer, Intercom, No. 1A (Mk. 2) for use at a 1st choice main station on installations with one exchange line and a non-multiple station.

Unit, Transfer, Intercom, No. 2 (Mk. 2) for use at 1st and 2nd choice main stations on installations with two exchange lines and with, or without, a non-multiple station.

Unit, Transfer, Intercom, No. 3 (Mk. 1) for use together with a Unit, Transfer, Intercom., No. 2 at the 1st choice main station on installations with two exchange lines and a non-multiple station.  The unit may also be used together with a Unit, Transfer, Intercom., No. 1 at 2 1st choice main stations on installations having one working exchange line but cabled for later expansion to take two exchange lines and with a non-multiple station.

Units, Transfer, Intercom, Nos. 1, 1A and 2 (Mk. 1) may still be met with on existing installations but will no longer be issued for new work.  All such units will be converted to Mk. 2 either in the field in accordance with Works Specification S504 or, when returned to stores, by Factory Dept. repair.

10. Common Constructional Details
Units, Transfer, Intercom, Nos. 1, 1A, 2 and 3 are of a standard overall size, the base being approximately 10.5in. by 7.25in. and the height 8.75in.  A standard black, moulded cover (Cover No. 5) encloses the mechanism of the unit which is mounted on a metal chassis of the same form for all the units.  The cover is located on the unit by slots in its lower edges, at the sides, which seat on four screws on the sides of the chassis.  These screws which secure the cover in position are trapped, and cannot be completely removed from the chassis, but when they are loosened the cover may be lifted off the unit.

Each unit includes a 25 conductor cord (Cord, Instrument, No. 25/02G, Brown, 72in.) terminated with a plug (Plug No. 2404).  The units contain exchange line and/or non-multiple station calling and clearing indicators, with associated bell (or buzzer), transfer keys, night-service and alarm cut-off keys and keys for switching a non-multiple station to the exchange lines.  The keys and indicators are mounted on the faceplate of the chassis.  The cover, when being lifted off, should be moved forward to clear the key handles which project approximately i in. in front of the unit.  Two recesses in the cover, one at each side of the unit, give access to one or two press-buttons, depending on the particular unit concerned.  The functions of the keys, indicators and press-buttons are described in C3021 and 3022.  Certain of the labels indicating the key functions are engraved on both sides and are reversible, as described in Q 3001, to enable a particular unit to serve at either a 1st or 2nd choice main station.

11. Unit, Transfer, Intercom, No. 1
This unit, as supplied, is fitted with one 'doll's eye' indicator (labelled EXCH) for exchange line calling and clearing.  Space in the unit, with accommodation on the faceplate, and the necessary wiring are provided for a second 'doll's eye' indicator which may be fitted to the unit locally (and labelled EXTN) for non-multiple station calling and clearing when the unit is to be used at a 2nd-choice main station on an installation with one exchange line and a non- multiple station.  The circumstances and method of fitting the EXTN indicator are described in C 3023.  The position of the second indicator on the faceplate is covered by a metal plate when the indicator is not fitted.  Internal strapping points are also provided to convert the circuit for alternative use of the unit at 1st or 2nd choice main stations, as described in C 3023.

The unit contains a trembler bell which can be operated by both indicators.  Two single-throw, locking lever keys are fitted, the TRANSFER key below the Exch indicator and the ALARM OFF key below the position for the EXTN indicator.  A label fitted below the keys is engraved on both sides and is reversible to indicate either that the ALARM OFF key only or that both keys are in use depending on the function of the unit in the installation.  The unit is fitted with one EXCH CALL press-button in the left-hand position and a dummy button in the right-hand position.  The circuit of this unit is shown on Diagram Q(L) 132 and the wiring on Diagram Q(L) 142.  The weight of the unit complete is approximately 10.25lbs.

12. Unit, Transfer, Intercom, No. 1A
This unit is fitted with two 'doll's eye' indicators, one (labelled Exch) for exchange line calling and clearing and one, (labelled EXTN) for non-multiple station calling and clearing.  The unit contains a buzzer (trembler bell without gong) which can be operated by both indicators.  Three lever keys are fitted on the faceplate below the indicators.  The left-hand key is a double-throw, locking key labelled ALARM OFF (NIGHT SCE) in the 'up' position and TRANSFER in the 'down' position (when used).  The centre and right-hand keys are single-throw, locking lever keys, labelled respectively ALARM OFF and EXTN TO EXCH.  The label fitted below the keys is reversible to suit the function of the unit in the installation, as described in 3001, and internal strapping points are provided to convert the circuit of the unit accordingly.  The unit is fitted with one EXCH CALL press-button on the left and a dummy button on the right.  These units contain a special relay (BZ) for ringing the non- multiple station.  The circuit of this unit is shown on Diagram Q(L) 133 and the wiring on Diagram Q(L) 143. The weight of the complete unit is approximately 14.1lb.

13. Unit, Transfer, Intercom, No. 2
This unit is fitted with two 'doll's eye' indicators (labelled EXCH 1 and EXCH 2) for exchange-line calling and clearing.  Space in the unit, with accommodation on the faceplate and the necessary wiring are provided for a third 'doll's eye' indicator (labelled EXTN) which may be fitted to the unit locally for non-multiple station calling and clearing when the unit is to be used at a 2nd-choice main station on an installation with two exchange lines and a non-multiple station.  The circumstances and method of fitting the EXTN indicator are described in Q 3001.  The position of the third indicator on the faceplate is covered by a metal plate when the indicator is not fitted.  The unit contains a trembler bell which can be operated by all three indicators. Internal strapping points are also provided to convert the circuit for alternative use of the unit at a 1st or 2nd choice main station, as described in Q 3023.  Three single throw, locking lever keys are fitted below the indicators and are labelled with a reversible label.  On the unit as supplied, the label is fitted to show only ALARM OFF against the centre key.  When reversed, the label shows TRANSFER against each outer key in addition to ALARM OFF against the centre key.

The label is reversed to suit the function of the unit in the installation, as described in C 3023.  This unit is fitted with two press-buttons, labelled EXCH CALL 1 on the left and EXCH CALL 2 on the right.  The circuit of this unit is shown on Diagram Q(L) 232 and the wiring on Diagram Q(L) 242.  The weight of the complete unit is approximately 11.5lbs.

14. Unit, Transfer, Intercom, No. 3
This unit is fitted with one 'doll's eye' indicator (labelled EXTN) for non-multiple station calling and clearing and contains a trembler bell operated by the indicator.  Three double-throw, locking lever keys are fitted below the indicator.  A single-sided label is fitted to designate the 'down' positions of the keys as EXTN TO EXCH 1, ALARM OFF and EXTN TO EXCH 2, respectively.  The 'up' positions of the keys are designated with a reversible label, which, on units as supplied, is fitted to designate the left and right-hand keys ALARM OFF (NIGHT SCE 2) and ALARM OFF (NIGHT SCE 1), respectively.  Reversed, the label shows the same designations for the outer keys and in addition shows TRANSFER against the 'up' position of the centre key.  The label is reversed to suit the function of the unit in the installation, as described in C3023 and an internal strapping point is provided to convert the circuit of the unit accordingly.  These units contain a special relay (BZ) for ringing the non- multiple station.  Dummy buttons are fitted to both press-button positions on this unit.  The circuit of this unit is shown on Diagram Q(L) 233 and the wiring on Diagram Q(L) 243. The weight of the complete unit is approximately 13.5lbs.

15. Plugs
The plugs are of three types:-
Plug No. 2404, which is part of each transfer unit.
Plug No. 2404A, which is part of Telephone, Intercom, No. 1/1.
Plug No. 4001A, which is part of Telephones, Intercom, Nos. 1/2 and 1/2A.

A single type of black, moulded body is used for the three types of plug. The base of the plug body measures 2.1in. by 3.2in. and its height is 1.5in.  Two 'trapped' screws are provided in the plug body for securing the plug to Jack No. 53 or Jack No. 54 (par. 17).  A screwed cable-entry gland projects at one end for approximately 1in.  A rubber sleeve and clamping ring fitted to the cable-entry gland have previously been included as parts of the plugs but these will in future be parts of Cords, Instrument, Nos. 25/01G, 25/02G and 38/02G , which are used with these plugs (see also Par. 16). Plugs Nos. 2404A and 4001A include a Buzzer No. 21, which is mounted on top of the plug.  The buzzer has a separate black, moulded cover (Cover No. 3) which includes two 'trapped' screws for securing it to the plug body.  The overall height of the plug is increased by the buzzer and its cover to 2.75in approximately.  The plug points, numbered front 1 to 40, are assembled in the form of a 'comb'.  The Plug No. 4001A is fitted with all points from 1 to 40. The Plugs Nos. 2404 and 2404A are fitted only with points 5 to 28.  The positions of the plug point are such that the No.2404 and 2404A plugs may be interchanged with a Plug No. 4001A on a Jack No. 54 without change of cabling to the jack points.  By this means, it is possible to use Telephones, Intercom, No. 1/1 initially and replace them later by Telephones, Intercom, No. 1/2 or No. 1/2A on an installation cabled to accommodate two exchange lines and ten stations but having initially only one exchange line and not more than five (exceptionally, six) stations.  The numbering of the plug-point terminations of the transfer units and telephones is shown on Diagram Q(L) 152.

16. Cords
The cords used on house-exchange telephones and transfer units are Cord, Instrument, No. 25/01G, Brown, 72in. (on a Telephone, Intercom, No. 1/1 ), Cord, Instrument, No.38102G, Brown, 72in. (on Telephones, Intercom, Nos. 1/2 and 1,/2A) and Cord, Instrument No. 25/02G, Brown, 72in. (on all Units, Transfer, Intercom).  When obtained separately, the cords will, in future, include (as part of the cord) the rubber protective sleeve at each end with its clamping and securing rings and the cord guide at the telephone, or unit, end.  These items have been included with the cords as the large diameter, approximately 1 inch, of the cords of present manufacture makes it impracticable to fit the parts once the cords have been made up.

Non-standard cord lengths are not stocked and requests for them should be avoided by attention to the installation layout, as described in C3023.

17. Jacks
Jack No. 53 and Jack No. 54 are used.  The former is required for all transfer units and for Telephone, Intercom, No. 1/1 on installations cabled for a normal maximum of five stations.  The latter is required for Telephones, Intercom, Nos. 1/2 and 1/2A, but it may be used with a Telephone, Intercom, No. 1/1 (see para. 15).  The construction of the jacks is the same for both types, except for the number of jack points fitted.  The jack points are numbered 1 to 40 and correspond to the plug points of the plugs described in par. 15.  The Jack No. 53 is fitted with jack points Nos. 5 to 28 but the Jack No. 54 is fitted with jack points Nos. 1 to 40.  The jack points are of the U-point type and are mounted on a black, moulded base (approximately 6.5in. by 3.5in.) open at the back.

Plug No. 2404A and Jack No. 53

Plug No. 4001A and Jack No. 54

The height of the jack base is 1in. and the total height of the assembly, with the plug screwed in position on the jack, is approximately 2.5in. with a Plug No. 2404 and 33in. with Plugs Nos. 2404A and 4001A.  Three slots in the base, one at each end and one at the side, are provided for cable entry to the back of the jack.  The slots in new jacks are covered by a thin 'knockout' web formed in the moulding.  Jacks reissued after repair will be accompanied by a sufficient number of small plugs Parts 1/SPL/391 to fill any previously used slots.

The plugs will be wrapped with the fixing screws.  Two wood-screws No. 8 x 1.5in. are supplied with each jack for use when fixing the jack to a wall or other support as described in Q3001.  A moulded baseplate, Part 1/SBA/4 , which may be fitted under the jack, is available for use if the jack has unavoidably to be mounted on a damp wall.  The baseplate is approximately 6.5in. by 3.5in. and its effective thickness is approximately 3 in.  Three wood-screws No. 6 x 1in. are supplied with the baseplate for fixing it to the wall and two screws 4 BA x 1in. for fixing the jack to the baseplate.

18. Junction Boxes
Two sizes of junction box are used and are known as Box, Junction, Intercom., No. 1 and Box, Junction, Intercom., No. 2.  Both boxes consist of a black, moulded base and cover containing four moulded terminal strips.  The covers of the No. 1 and No. 2 boxes are known as Cover No. 1 and Cover No. 2, respectively.  The No. 1 box has 30 terminals per strip and No. 2 box 48 terminals per strip.  The terminals are in two rows and are numbered 1, 3, 5, etc., on the left, and 2, 4, 6, etc., on the right of the strip.

Each terminal provides a front and a rear screw connection and the two rows are staggered in position so that corresponding terminals on adjacent strips may be connected together by lengths of bare wire passed through them across the front of the strips.  Wire, Copper, Tinned, No. 18 S.W.G. is used and a number of lengths of this wire cut to bridge the four strips is included with each box.  Jumper cross-connections between terminals may also be made with insulated wires.  The portions of the terminals at the back of the strips provide screw connections for terminating the house-exchange system multiple cable.  The strips are grooved at the back to accommodate the cable ends and a cable clamp is fitted at each end of each strip.  A bonding strip to connect together the sheaths of the cables, via the cable clamps, is included with each junction box.  The method of using the bonding strip is described in C3023.  Provision is made for cable entry at either end of the box, via four slots in each end of the cover.  The slots in new covers are filled by a thin 'knock-out' web formed in the moulding.  Old covers may be reissued with used slots (if more than two) repaired by means of a small moulded plug, Part 1/SPL/392 for Covers No. 1 and Part 2/SPL/392 for Covers No. 2.

Three rubber feet, Parts I/SBU/6, and three wood-screws No. 10, 1.5in. are included with each box for fixing.  The overall dimensions of the Box, Junction, Intercom., No. 1 are approximately 8.75in. x 7.5in. x 2.25in. and it weighs 4lb.  The Box, Junction, Intercom, No. 2 is approximately 12in. x 8in, x 2.25in. and weighs 5lb. Labels No. 226... and Labels No. 227... may be obtained separately from the Supplies Dept., for use with the junction boxes, as described in C3023.

Box, Junction, Intercom No. 1 (right) and No. 2 (left)

Box, Junction, Intercom No. 2 with cover and one terminating strip removed

Box, Junction, Intercom No. 1 with cover removed

Box, Junction, Intercom No. 2 showing front and rear of terminating strip

19. Non-multiple Station Telephones
Normally a Telephone, No. 1/232... with Bell-set No. 26 or a Telephone No. 332 is used, but other standard alternative C.B. or automatic A.S.T.I.C. handset telephones may be used in appropriate circumstances.

20. Extension Bell, etc
There are no special types of extension bell for use on the house exchange system. Bells No. 56E, Bells No. 64 and other standard types are according to circumstances, as described in C3023.  Descriptions of the bells and general conditions of installation are given in M0060.  General information on lamp-calling signals is given in M0663.

21. Additional Receivers
A Receiver, Watch, No. 6L and a Hook, Receiver, X are used.

22. Labels
Particulars of labels used in junction boxes are given in par. 18.

Introduced circa 1935.

Made by Ericsson Telephones Ltd (ETL).

TELECOMMUNICATIONS INSTRUCTION
C MARKETING INSTALLATION
3 Internal
C 3021
Issue 1, Dec 1970

HOUSE EXCHANGE SYSTEMS No's 1 AND 2
Operating Procedure

1. Scope of Instruction
This instruction describes the operating procedure necessary to establish a. connexion on the house Exchange system, and is intended as a guide for installing staff when testing-out an installation after completion of fitting and wiring. The information is arranged under the following headings

For detailed circuit operation, see C3022.

2. Terms
The terms "Multiple station" and "Non-multiple station," respectively, replace the terms "Internal Extension station" and "External Extension station" employed in the previous issue of this Instruction.
 

MULTIPLE STATION PROCEDURE

3. Key Operation
The mechanical arrangement of the keys on "Telephones, Intercom Nos. 1/1 and 1/2" is such, that when depressed consecutively (except while conference key "C" is depressed) only one key may remain fully operated at any time. If a local key is in the operated position, the depression of a second local key completely restores the first. If, however, the conference key is first depressed, or is depressed after only one local key has been depressed, all the remaining keys may subsequently be depressed simultaneously, and will remain operated (in the speaking position). The conference key and all local keys held by it will be released if an exchange key is depressed. or if the handset telephone is replaced on its rest. If an exchange key is in the operated position, the depression of a local key or of the second exchange key will partially release the first key, which will then take up a "hold" position (see par. 13).

4. Key re1ease
When any key (or all of the keys) has been operated, replacement of the handset on its rest automatically restores all keys to normal. On telephones having two exchange keys, i.e., "Telephones, Intercom., No. 1/2", either exchange key may be released from the "hold" position by operating its associated trigger - RELEASE - key without replacing the handset and without releasing a local key or the other exchange key, one or the other of which, in "hold" circumstances, will be in the operated position at the time. The release of an exchange key by means of the trigger key is effected by pulling the trigger towards the exchange key until a "click" is heard denoting the release of the exchange key mechanism. The trigger key will not release an exchange key from the fully-operated position.

5. Local call - Called station free
A call from one multiple station to another or to a non-multiple station is made by lifting the handset at the calling station and fully depressing the plunger key adjacent to the required station number. In the fully depressed position, this key completes a circuit for operating the telephone buzzer at the called station. When pressure on the key is released, the key automatically takes up the speaking position. The call is answered by the handset being lifted at the called station and conversation is then possible.

6. Called station engaged on Local call
Local calls are not secret; if, therefore, the called station is engaged on a local call, the calling station will break-in on the conversation.

7. Called station engaged on exchange call
Except as described in par. 24, if the called station is engaged on an exchange call, the buzzer at the calling station operates when the key for the called station is fully depressed. This serves as an engaged signal to the calling station and the conversation of the called station on the exchange line cannot be broken into or overheard.

8. Called station holding exchange line
If the called station is holding an exchange line, while engaged on a local call, the calling station buzzer will be operated (as described in par. 7) but the called station's local call will be broken into and the calling station can listen to the conversation.

9. Conference call
When it is desired to make a. conference call, the stations which will participate are first called individually, as described in par. 5. When the attention of these stations has been obtained, the conference key at the calling station is depressed, followed in succession by the keys corresponding to the stations concerned. The. conference may then proceed. The conference connexion is released completely by replacing the handset on its rest, or by depression of an exchange key. Therefore, if a station which has set up a conference call makes or receives an exchange call, the conference call is automatically terminated. Any of the called stations may break away from the conference to make or receive an exchange call in the normal manner, as described in pars. 11 to 13, and subsequently, may return to the conference by momentarily depressing the plungers on the handset rest, to release the exchange key. If a called station on conference calls another local station, by depressing the appropriate key, conversation between the two will be overheard by other parties to the conference. It is not possible for the calling station to release stations individually from a conference call.

10. Outgoing exchange calls - From stations having full facilities
Multiple stations with full facilities have direct access to exchange lines, as described in the following pars. 11 to 13.

11. Exchange line engaged test
Except as described in par. 25, an exchange line may be tested by depressing the relevant exchange key without removing the handset from its rest. If the exchange line is engaged, the calling station buzzer will operate. Under these conditions, the exchange key releases automatically when pressure on it is removed, [The engaged test also operates on engaged exchange lines if the exchange key is depressed after the handset has been lifted. The exchange key then remains in the operated position until the handset is replaced or until another key is depressed.] For procedure at a main station having visual exchange-line engaged signals, see par. 26.

12. Exchange line free
If a buzzer signal is not received on depression of an exchange key, the exchange line is free; connexion to the exchange Line may then be obtained by lifting the handset and depressing the exchange key. This operation calls the exchange, if it is manual, or if the exchange is automatic, the caller receives dialling tone and may proceed to dial the required number.

13. Holding exchange call while snaking a local call
If, during the progress of an exchange call, the calling station desires to speak to one of the local stations, the depression of the local key corresponding to the wanted station automatically releases the exchange key to an intermediate position, in which a "hold" condition is presented to the exchange line. At the termination of the local call, the exchange key may again be fully depressed and the exchange-line conversation resumed.

14. Holding one exchange call while making a second exchange call-On installations with two exchange lines, if a station (while engaged with one exchange call) desires to make a call over the second exchange line, the depression of the second exchange key releases the first key to the hold" position At the termination of the second call, the first call may be resumed by again depressing the first exchange key; this, in turn, releases the second key to the "hold" position. The second key may then be completely released by means of its associated trigger key (par. 4).

15. Calls from stations having restricted facilities
It is not possible to obtain direct access to exchange lines from stations with restricted facilities. Such stations desiring to make an exchange call must first call the main station, as described in par. 5, and advise the main station attendant of the exchange and number required. If the call is to be permitted, the caller is asked to replace the handset on its rest and await recall from the main station. The call is then set up by the main station attendant and transferred to the calling station, as described in par. 22.

16. Incoming exchange calls, and main station procedure - Control by main station
All incoming exchange calls are first received at the main station (or other multiple station acting as main station). The incoming calling signal operates an indicator in the unit equipment ("Unit, Transfer Intercom., No. 1, 1A or 2") fitted at the main station. An audible signal (by bell or buzzer) is also given. The audible signalling apparatus, when not required, may be disconnected by means of the ALARM OFF key on the transfer unit On installations with two exchange lines each line has an individual indicator, but a common audible alarm serves both. The main station attendant answers the call by lifting the telephone handset and depressing the appropriate exchange key. If the call is for another station it is transferred to that station as described in pars. 20 to 22 or par. 32.

17 Control by 2nd-choice main station
On installations having a 2nd choice main station all the functions of the 1st-choice station (except as regards non-multiple station calls, the procedure for which is given in par. 33) may be transferred to the 2nd choice station by means of the TRANSFER key or keys on the 1st choice main station transfer unit. Incoming exchange calls are received at the 2nd choice main station and dealt with in the same manner as described in par. 16.

18. Control by multiple station with extension bell
At a multiple station arranged for the receipt of exchange calls, the calling signal is received on an extension bell (or equivalent device) from the main station transfer unit. On installations with two exchange lines, one extension bell serves both lines and it is therefore necessary for the attendant to test for the calling line. This is done by lifting the handset and depressing one of the exchange keys or each exchange key in turn. [No. 1 exchange line should be tested first to minimize the number of occasions on which a false call will be given to the public exchange]. If the call is for another station, it is transferred as described in pars. 20 to 22 or par. 32.

19. Holding one exchange call while receiving a ,second exchange call
On an installation with two exchange lines, if the main station (or station serving as main) is engaged on one exchange call, another exchange call signalled on the second line may be answered by depressing the second exchange key, thus releasing the first exchange key to the "hold" position (as described in par. 13). If the second call is for another station, it may be transferred as described in pars. 20 to 22 or par. 32. Resumption of the first call and release of the second call may be effected as described in par. 14.

20. Transfer of exchange calls - Station with full facilities
An exchange call, originated (or received) at a main station or multiple station may be transferred to another multiple station with full facilities. At the Station transferring the call, the local key corresponding to the required Station is depressed, thus releasing the exchange key to the "hold" position (see par. 13), and the required station i asked to "pick up" the call on the exchange line concerned. To do this, the appropriate exchange key is depressed at the called station, whereupon, the buzzer operates at that station and buzzer tone is passed back to the first station where it is heard in the handset receiver. The handset at the first station is then replaced on its rest. This causes the buzzer at the called station to stop operating and the exchange call to be connected automatically at that station. The transfer is then complete.

21. Station engaged with one exchange call while holding another
On installations with two exchange lines a station, while engaged with one exchange call and having made or received a second exchange call (as described in par. 14 or par. 19) may transfer one of the calls to another station with full facilities, while holding the first. call. The procedure for transferring the call is as described in par. 20, except that on receipt of the buzzer tone from the station "picking up" the call, the appropriate exchange key at the first station is released by means of the associated trigger key (see par. 5) and not by replacing the handset on its test. The call held may then be resumed by again depressing the relevant exchange key or it may, in turn, be transferred to another station (as described in par. 20).

22. Station with restricted facilities
A main station may transfer an exchange call to a multiple station with restricted facilities by proceeding as described in par. 20, except that on receipt of the buzzer tone from the other station, the main station attendant will depress and hold down the EXCH CALL button (on the main station transfer unit) corresponding to the exchange key on the telephone, then release the appropriate exchange key on the telephone, and lastly, will release the EXCH CALL button. The EXCH CALL button must be held operated until the exchange key on the telephone has been released. The transfer of the call is then complete. Any station, other than the main station, desiring to transfer an exchange call to a station with restricted facilities must first transfer the call to the main station by the procedure described in par. 20.

23. Transfer of exchange calls to non-multiple station
The main station procedure for transferring an exchange call to a non-multiple station is described in par. 32. A multiple station, other than a main station, desiring to transfer an exchange call to a non-multiple station must first transfer the call to the main station by the procedure described in par. 20.

24. Special facilities - Multiple station calling main station engaged on exchange call
Where the facility is given (only on installations with two exchange lines), to call the main station while it is engaged on an exchange call, the calling station buzzer does not operate when the calling station fully depresses the local key associated with the main station, as described in par. 6; instead, the main station buzzer operates as if the station were disengaged. To answer the call, the main station attendant depresses the local key associated with his own station. This releases the exchange key to the "hold" position (see par. 13) and connects the main station handset to the local calling line. If it is then desired to transfer the held exchange call to the calling station, the key associated with that station on the main station telephone should be depressed and the call transferred, as described in par. 20. If the procedure is not adopted, buzzer tone will not be heard in the main station receiver, when the calling station depresses the relative exchange-line key, and the main station attendant will have no indication that the transfer of the call is in process.

25. Exchange-line monitoring or trunk-offering facility
Where the facility is given for a station to monitor on exchange lines (normally limited to a 1st choice or 2nd choice main station) the exchange line engaged signal, as described in par. II, is not given; instead the calling station with the monitoring facility may break-into, or listen to, an exchange call proceeding at another station on the system.  This facility is for limited use only, see C3001.

20. Visual exchange-line-engaged signal
On installations where the facility is given for the main station to have visual exchange-tine-engaged signals, these are given by the indicators in the main station transfer unit ("Unit, Transfer, Intercom., No. 1, 1A or 2"). With this facility, it is not necessary for the main station attendant to test exchange lines by depressing the exchange keys (as described in par. ii) because the presence, or absence, of the indicator signal will indicate whether the exchange line concerned is engaged or free.
 

NON-MULTIPLE STATION PROCEDURE

27. General
Except under night service conditions (as described in pars. 36 to 3), all calls originated by a non-multiple station and all incoming exchange calls for such a station are passed via the main station and require the services of the main station attendant to complete the connexions. Local calls made to the non-multiple station from multiple stations, although passing via equipment at the main station, are made without the intervention of the main station attendant.

28. Non-multiple station calling main station
To gain the attention of the main station, the handset at the non-multiple station is lifted and this results in the operation of the extension indicator (and associated alarm bell or buzzer) in the main station transfer unit, ("Unit, Transfer, Intercom., No. 1A or 3"). To answer the call, the main station attendant lifts his telephone handset and depresses the local plunger key corresponding to the non-multiple station.

29. Local calls - Outgoing
The non-multiple station first calls the main station (as described in par. 28) and advises the attendant of the local station required. The main station attendant then calls the wanted station and, in turn, asks the latter to call the non-multiple station (as described in par. 5) i.e.  the call is reverted.

30 Local calls - Incoming
Incoming calls are signalled at the non-multiple station in the normal way on the magneto bell associated with the non-multiple station telephone. Local calls to the non-multiple station are made directly (as described in par. 5) and are answered at the non-multiple station by lifting the telephone handset.

31. Outgoing exchange call - Control by main station
The non-multiple station first calls the main station as described in par. 28 and either asks to be connected to an exchange line or advises the attendant of the exchange and number required. Except as described in par. 26, the main station attendant tests the exchange lines for a free line (see par. 11). When a free line has been obtained, the attendant may operate the EXTN TO EXCH key on the main station transfer unit to connect the non-multiple station to the exchange line so that the non-multiple station may proceed to set up the call. Alternatively, the main station attendant may set up the exchange call and, then, transfer it to the non-multiple station (as described in par. 32). On completion of the call, when the non-multiple station replaces the handset on the telephone, the extension indicator on the main-station transfer unit operates to give a clearing signal to the attendant, who then restores the EXTN to EXCH key On the transfer unit ("Unit, Transfer, Intercom., No. 1A or 3"). See par. 33 for control by a 2nd choice main station.

32. Incoming exchange call - Control by main station
As described in par. 16, all incoming exchange calls are first received at the main station or other multiple station acting as main station. If an exchange call is to be transferred from the main station to a non-multiple station, the main-station attendant calls the non-multiple station (par. 5) and then operates the EXTN TO EXCH key on the transfer unit. The subsequent procedure at the main station is as described in par. 31. For control by a 2nd choice main station, see par. 33.

33. Control by 2nd-choice main elation
If control has been transferred to a 2nd choice main station (by operating the TRANSFER key or keys at the 1st choice main station) the 2nd choice station will receive, the calling signals from the non-multiple station but the facility for switching the non-multiple station to an exchange line will remain at the 1st choice main station. Therefore, if the non-multiple station desires an exchange call, the 2nd choice main station attendant must go to the 1st choice main station to carry out the necessary switching. If the attendant remains at the 1st choice station until the call terminates, the control must be reverted to the 1st choice station, by restoring to normal the TRANSFER key (or keys) so that the clearing signal for the non-multiple station call may he received there. If the attendant returns to the 2nd choice station to await the clearing signal, he must an back when he receives it, to the 1st choice main station to restore the EXTN TO EXCH key.

34. Control by a multiple station with extension bell
When a multiple station, fitted with an extension bell from the main Station transfer unit, is in control on an installation equipped for one exchange line only but having a non-multiple station, the exchange and non-multiple station calling signals will be received on the same bell. In such cases, the non-multiple station calling signal will be a continuous ring on the bell whereas the exchange calling signal will be intermittent. The attendant, desiring to connect the non-multiple station to the exchange line or to transfer an exchange cull to the non-multiple station, must go to the main station and proceed as described in par. 31 or 32. On installations with two exchange lines and a non-multiple station, one extension bell serves both exchange lines see per. 18) but the non-multiple station calling signals are extended to a separate bell.

35. Recalling main station while holding exchange call; transfer of exchange call to multiple stations
A non-multiple station user engaged on in exchange call and desiring to call the main station without releasing the call, may do so (except for certain outgoing calls via automatic exchanges as described below) by "flashing," i.e., by repeatedly depressing and releasing the plunger (or plungers) of the handset rest on his telephone so as to cause the intermittent operation and release of the extension indicator at the main station. The attendant at the main station lifts his handset, depresses the exchange key of the exchange line concerned and, then, restore, the EXTN to EXCH key on the mum station transfer unit, thus transferring the exchange line to the control of the main station; the attendant then calls the non-multiple station, by depressing the associated local key, and asks the reason for the recall, if required, the call may than be transferred to another station (am described in pure. 20 to 22). Alternatively, the call may be reconnected to the non-multiple station by re-operating the EXTN to EXCH key. If the non-multiple station recall signals are received at a 2nd-choice main station (see par. 33 or at a multiple station with extension ball (see per 34), the attendant must go to the 1st-choice main station to answer the call. If the non-multiple station is engaged on an exchange call which has been originated at the House Exchange system by direct dialling (either from the non-multiple station itself or from another station on the system and subsequently transferred to the non-multiple station), the non-multiple station cannot recall the main station without releasing the exchange call.
 

NIGHT SERVICE

36. Multiple station
If a multiple station is arranged to receive exchange calls on night service, the calling signals from the main station transfer unit will be received on an extension bell. The calling signals will be given simultaneously at the main station and at the multiple station, and may be answered at either.

37. Non-multiple station
The non-multiple station may be permanently switched to an exchange line during the night, by the operation of two keys, the EXTN to EXCH key and the ALARM OFF (NIGHT SCE) key, on the main station transfer unit ("Unit, Transfer, Intercom., No. 1A or 3"). As a warning against a mis-operation an indicator signal is given if only one of the two keys is operated or if other keys are also operated. Under night service, the non-multiple station may make (and receive) exchange calls directly over the night-service exchange line in the normal manner appropriate to a direct-exchange-line user. Multiple stations on the installation may use the night-service exchange line when it is not in use by the non-multiple station, but calls so made will not be secret from the non-multiple station. Similarly, a night-service call made by the non-multiple station will not be secret from the multiple stations.

38. Local calls under night service conditions
On installations with only one exchange line, local calls between a non-multiple station on night service and multiple stations on the system cannot be made. On installations with two exchange lines, a multiple station may call the non-multiple station on night service, via the public exchange over the second exchange line. Similarly, the non-multiple station may call a multiple station (if the main station is attended to receive the call) via the public exchange over the second exchange line.

Last revised: January 20, 2025