P.A. 450 POLICE SYSTEM

POLICE TELEPHONE & SIGNAL SYSTEM
PA 450
General Description

1. Contents

2. Scope of Instruction
This Instruction describes the features and facilities of the Police Telephone and Signalling System PA 450.

3. General
The PA 450 System has been introduced to supersede the PA 150 TD System for new provincial installations.  The system has been designed to use standard P.M.B.X. indicator calling switchboards or lamp calling switchboards associated with P.M.B.X. and P.A.B.X. No. 2 and No. 3 installations.  A new-style street call-post has been introduced, based on the type used by the Metropolitan Police, in which a single handset telephone is provided for use by both the police and the public.  Each street call-point is connected to the switchboard by a direct line, the auxiliary equipment required to provide the facilities described below being made up from standard components.

Facilities provided by the system are as follows:

1. Automatic calling; a momentary operation of the ring key associated with a call-point circuit starts the calling signal, which will then continue to be sent out automatically until the call is answered or cancelled.

2. Calling signals can be given simultaneously to a number of call-points, by the operation of the appropriate keys.

3. Call cancellation, if the call is not answered, is effected by a second momentary operation of the ring key.

4. A lamp signal, flashing with the same periodicity as the calling signal, 0.75 sec on and 0.75 sec off, is given at the call-point. An audible alarm, working in parallel with the lamp signal, may also be provided.

5. A ‘proving’ circuit indicates to the operator that the signal lamp is operating satisfactorily.

6. Call-points may be either street posts or kiosks. Internal illumination of the Perspex signs in the street posts enables them to be readily identified after dark.

7. A single handset telephone is provided for the use of both the police and public. The switchboard is called by the loop extended from the call point when the telephone handset is lifted. The call is answered at the switchboard as for a normal extension. The signal lamp at the call-point does not glow when a call is originated there.

8. Indication of when a call-point is being called, or is in use, may be given by lamps suitably mounted on a wall map.

9. Normal P.B.X. facilities are available. Any call-point or any internal or external extension can be connected to the public exchange, but dialling facilities are not available from the call-points.

POLICE HEADQUARTERS EQUIPMENT

5. Switchboard
The type of switchboard to be used will depend upon the number of circuits to be terminated and the traffic loading.  The call-point circuits have been designed to work to Switchboards AT 3796 (65 line), Sections, Switch, P.M.B.X. No. 1A or Sections, Switch, P.B.X., SA 7560 (used at P.M.B.X. or P.A.B.X. installations).  Table 1 gives the maximum number of circuits which may be terminated using these switchboards. P.A.B.X.s Nos. 2 and 3 have not been included as the space for call-point circuits will be determined by whatever space is available after the P.A.B.X. requirements have been satisfied.

Private circuits are not included in this table but, as they are accommodated in the exchange or extension jack field, it should be assumed that the number of these circuits will correspondingly decrease the number of exchange and/or extension lines that can be terminated.  120 call-points is the maximum number of call-points that can be terminated on a P.M.B.X.. No. 1A installation, using the standard face-equipment layout.  However, by using a non standard arrangement, it is possible to increase the capacity (see P 3305).  Traffic loading may justify the provision of a P.M.B.X. No. 1A installation before the maximum capacity of the non-multiple type switchboard has been reached.

6. Call-point terminations
Auxi1iary equipment is required on each call-point circuit at the switchboard end to provide the facilities described in par. 4.

(a) Line Circuits Type ‘A’ (24v and 50v) are used for all call point terminations on Switchboards AT 3796, and also for those call-points terminating at a P.M.B.X. No. 1A installation with a loop resistance exceeding 300 ohms or on which the standard P.B.X. exchange line + extension limits are exceeded (Strip-mounted Set PA 454).

(b) Line Circuits Type ‘B’ are used for those call points terminating at a P.M.B.X. No. 1A installation with a loop resistance not greater than 300 ohms and which do not exceed the exchange line + extension limit of the PBX (Strip-mounted Set PA 455).

(c) Line Circuits Type ‘C’ are used for all call point terminations on standard P.A.B.X. Nos. 2 and 3 installations.  The line circuits are strip-mounted, Types ‘A’ and ‘C’ having two circuits per mounting base and Type ‘B’, having three circuits per mounting base (Strip-mounted Set PA 464).  It has a ballast battery feed and signalling resistance limit of 170ohm.

7. Transmission Limits
Street call-points are rarely connected to a public exchange, and then usually only for local calls.  For this reason some relaxation in the standard of transmission can be permitted.  For an exchange line and extension line to a call-point using Line Units Type A and C, transmission will be satisfactory providing the sum of the losses do not exceed 10 dB/10002.  For Line Unit B the transmission will be satisfactory provided that the signalling resistance is within the specified limits.

 Transmission and signalling limits for this system are detailed in TRANSMISSION, Telephone, B 3573.

8. Common equipment
(a) P.M.B.X. installations. One set of common equipment is provided per installation.  It consists of two strip-mounted sets fitted together at the top of the first equipment rack.  In earlier versions of the common equipment, the two strip-mounted sets were combined to form one unit but later versions have the equipment split into two separate strip-mounted sets, connexions between the two being made locally on installation.

(i) Strip-mounted Set PA 461 is a standby ringing vibrator.  Should the mains-energized ringing supply fail, the standby vibrator start and change-over circuits are automatic.  An alarm contact is provided so that indication of ‘ring fail’ may be given.  If the P.B.X. has ‘ring start’ facilities, the vibrator may be connected to supply the ringing current to the switchboard in the event of failure in the main ringing supply.

(ii) Strip-mounted Set PA 462 contains two circuits for interrupting the ringing supply current at approximately 0.75 sec on and 0.75 sec off, for flashing the street call-point lamps.  The two circuits are arranged so that normally the ‘X’ circuit is working, but change-over to the ‘Y’ circuit may be effected by moving a U-link in the test jack fitted to the Strip-mounted Set PA 461. An alarm is not given if the interruption circuit fails.  This strip mounted set also includes the rack fuse-alarm relays.  One relay is fitted and wired initially and wiring is provided for a further relay.  If more than two relays are required, mounting space exists, but wiring for these additional relays will have to be provided locally.

(b) P.A.B.X. Nos. 2 and 3 installations
One set of common equipment is provided per installation.  It consists of one Strip-mounted Set PA 465 fitted at the top of the first equipment rack and contains two circuits for interrupting the ringing supply current at approximately 0.75 sec on and 0.75 sec off for flashing the street call-point lamps.  The two circuits are arranged so that normally the ‘X’ circuit is working but the change-over to the ‘Y’ circuit may be effected by moving a U-link in the test jack.  An alarm is not given if the interruption circuit fails.  This strip mounted set also includes the rack fuse-alarm relays. One relay is fitted and wired initially and wiring is provided for a further relay.  If more than two relays are required, mounting space exists but wiring will have to be provided locally.

9. Apparatus rack
One or more Racks, Apparatus, No. 15 (Drawing - EC1298) are required for mounting the auxiliary equipment associated with the call-point terminations.  Diagram PA 482 shows a typical layout for one of these racks.  The line circuit equipments are provided as required, and are numbered downwards, the first equipment being fitted immediately beneath the common equipment.  At P.M.B.X. No. 1A installations, there may be a mixture of Type ‘A’ and Type ‘B’ circuits.  The two types should be grouped separately, either on the same rack if the number of circuits is small, or on separate racks if the number warrants more than one rack.  This will simplify the cabling to the M.D.F. where the cables terminate on separate connexion strips, and enables either type to be connected to any particular call point circuit.

Only one set of common equipment is provided per installation and, if more than one rack is needed to accommodate the line-circuit equipment, the additional racks will not have the common equipment fitted.  Each rack is equipped with its own battery distribution in the form of a fuse panel. The fuse alarm relays are included in the common equipment (see par. 8).

10. Ringing supply
As automatic ringing is used for signalling the police posts a continuous ringing supply is necessary.  This should be provided in accordance with POWER, General, S 3801.

11. Power supplies
At P.M.B.X. installations the headquarters equipment for the PA 450 system is designed to operate at the normal P.B.X. voltage (24V).  As it is essential that the operation should be independent of mains failure or similar interruptions, a single-battery float power plant should be provided in accordance with POWER, General, S 3320.  A power lead should not be used. At P.A.B.X. Nos. 2 and 3 installations the 50v battery supplying the P.A.B.X. should be used.

STREET CALL-POINT EQUIPMENT

12. Call Points
Street call-points may be either in the form of Posts, P.A. or kiosks.  The Posts, P.A. are supplied, and installed, by the Post Office on a rental basis, but kiosks, when required, are supplied and installed by the Police authorities.  In the latter case, the P.O. will install, and maintain, the telephone and signalling equipment and arrangements should be made locally with the Police authorities for incorporating the necessary space and the fixing and mounting positions required for this equipment when the kiosk is erected.

13. Posts, P.A. Nos. 2 and 3
It consists essentially of a cast-iron shell, approximately 1 ft. x 1 ft. 6 in. base dimensions by 7 ft. 6 in. high (the Posts, P.A. No. 2 also has a base 1 ft. 6 in. deep below ground level) surmounted by an amber signal light. Wooden shelves divide the interior into three compartments.

The top compartment contains the telephone and an internal lamp for illuminating the Perspex signs around the top of the post and in the door to the compartment.  This door is held closed by a ball catch and is fitted with a door-closing spring to prevent it being inadvertently left open.  The lower two compartments are fitted with locks (Locks Nos. 22 and 23) and are normally accessible to the police only.  The door to the centre compartment opens downwards and is arranged to form a writing shelf.  This compartment also contains a small shelf for holding writing materials, etc., and also the switches for controlling the internal lighting and for testing the signal lamps.

The bottom compartment contains the signalling unit and power supply cut-outs, etc.  A specially designed shelf in this compartment provides storage space for a first-aid kit (supplied by the Police authorities) and a policeman’s cape.

A Key, Lock, W is supplied with each post for use with the locks. Additional keys, if required, may be supplied by the P.O. in accordance with STORES, General, K 0011.  The posts, when supplied, are finished white inside and azure-blue outside.

The weight of the Post, P.A. No. 2 is approx. 7 cwt.  This has been reduced by approx. 2 cwt. in the Post, P.A. No. 3 by using a different manufacturing technique enabling thinner section material to be used. In addition, the base of the Post, P.A. No. 3 does not extend below ground level, but is secured by rag-bolts to a concrete foundation.  Otherwise, the details and layout of the equipment are identical in the two posts. Posts, P.A. No. 3 are the superseding item and will be the standard issue when stocks of Posts, P.A. No. 2 are exhausted.

14. Kiosks
The design of kiosks is the responsibility of the Police authorities, but particulars of the dimensions, and the methods of fixing the public door, signalling equipment and telephone should be supplied to the Police authorities so that suitable fixing facilities may be provided.  These details should be obtained from Drawing EC 2072.  The lantern used with the kiosk equipment is the Lantern, P.A. No. 1.  It will be necessary for the police authorities to provide a suitable bracket on the kiosk to which the lantern may be fitted.  Fixing is effected by three bolts and nuts supplied with the lantern and the Police authorities should be supplied with a copy of Diagram PA 126 (which is a dimensioned sketch of the drilling required for fixing the lantern) so that the brackets may be drilled accordingly.

15. Audible alarm
If required, an audible alarm may be fitted at the call-points, in addition to. the visual signal. A Bell No. 61 is used for this purpose at a Post, P.A. No. 2 and No. 3 or for an external alarm on a kiosk.  If an internal bell is required at a kiosk, a Bell No. 64D should be used.

16. Unit, Signalling, P.A. No. 2
This is the standard signalling unit fitted in Posts, P.A. No. 2 and No. 3 and in kiosks. It contains a high-voltage type relay which responds to the interrupted ringing current sent out from the line-circuit equipment at the switchboard when the post is being called. A contact of this relay completes the circuit for the signal lamp.  A second high-voltage relay in the signal-lamp circuit operates with the lamp and returns an earth signal to the switchboard to give the operator an indication that the signal-lamp is flashing.  This relay will not operate if the signal-lamp is disconnected.  As this unit has mains voltage connected to it, it is essential that due precautions are taken to ensure that the mains supply is disconnected before the cover is removed.

The Unit, Signalling, P.A. No. 2 was superseded by the Relay-Switch No. 3201 NL 1-15 AW.

17. Circuit diagrams

In earlier installations the ringing vibrator circuit and the flashing and miscellaneous circuits were mounted as one unit wired to Diagram PA 453.

18. Drawings

P.O. ENGINEERING DEPT.
ENGINEERING INSTRUCTIONS
TELEPHONES
STATIONS
P 3301
Issue 3, 18.3.63

POLICE TELEPHONE AND SIGNAL SYSTEM PA 450
Installation of Call-points

1. Scope of Instruction
This Instruction describes the erection and installation of the equipment required at the street call-points for the Police Telephone and Signal System PA 450. Its contents are arranged as follows:-

2. General
The call-point equipment Consists of a telephone and signalling unit, together with associated signal lamp, housed in either a metal street post or in a kiosk of suitable design and situated in a prominent position in a public thoroughfare.  The street post currently used for new work is the Post, P.A., No. 3.  This supersedes the Post, P.A., No. 2 which is similar in appearance but made use of a different method of construction.  The telephone is so mounted as to be readily accessible for use by either police or public.  A general description of the equipment is given in P 1301.

3. Choice of Call Points
The police authorities will decide whether Posts, P.A. No. 3 or kiosks will be used.

4. Siting of call-points
The choice of sites for the call-points is the responsibility of the police authorities, who will also negotiate all wayleaves necessary for the erection of the call-points.  Assistance should be given to the police authorities in deciding final locations so that, wherever possible, difficult cabling operations may be avoided and to ensure that, when erected, each position gives easy and safe access to the telephone compartment and maximum possible shelter from prevailing wind and rain.

5. Earth connexions
An efficient earth is essential at each street call-point and arrangements should be made to sink an earth plate during the erection of all posts and kiosks.  The method adopted should be in accordance with PROTECTION, General, S 3901. If an earth circuit-breaker is required, it should be fitted in the bottom compartment of the post.

6. Lead-in cables
All cables to the posts should be led-in direct from underground.  Where it is not possible or economical to connect with underground cables direct, the overhead line should be terminated on a suitably located pole or building, and led-in by means of underground cables from that point.

7. Lead-in pipes
Two Bends, Asbestos-cement, No. 3, one for the telephone cable and the other for the power cable, should be set into the base of each post during its erection.  To prevent the entry of gas, the pipes should be sealed in accordance with LINES, Underground, K 3003.

8. Erection of Posts, P.A. No. 3
The Post, P.A., No. 3 should be set on a firm concrete foundation.  An excavation should be made of approximate dimensions 2 ft. x 1 ft. 6in. x 1 ft. 6 in. deep.  The actual dimensions of the foundation provided will depend upon the situation and the nature of the ground. The depth may be decreased to 1 ft. if a larger area can be provided, but each case will have to be decided on the local conditions.  After positioning the lead-in pipes (see par. 7), the excavation should be filled with ‘A’ quality concrete and four Bolts, Foundation, Indented, No. 1 (or equivalent) set in the concrete.
[NOTE: ’A’ quality concrete consists of one part of Portland cement, two parts of sand and four parts aggregate. The aggregate comprises clean, screened river ballast, gravel stone or other approved material graded in size up to 0.75 in.]

A simple wooden or metal template (prepared locally) should be used to ensure the correct setting of the lead-in pipes and foundation bolts. Care should be taken to ensure a level surface of the finished concrete.  When laid, the foundation should be protected from the action of frost, shielded against too-rapid drying by exposure to the sun or wind, and guarded for at least 48 hours, to ensure that it will be set thoroughly before erection operations are commenced.

9. Before the erection of the post, the surface of the concrete should be thoroughly cleaned and a bedding of cement-mortar laid to a depth of 0.5 in. over that part of the surface on which the base flange will seat.  The post should then be set in position and secured by the foundation bolts.

10. The cement-mortar should then be struck off level with the inside surface of the concrete and, on the outside, the mortar should be trowelled to form a fillet around the post flange, to assist in the drainage of water.  The concrete inside the post should be coated with bituminous compound to form a seal against the ingress of moisture.

11. Fitting of lantern glass
To prevent the entry of rain and dust into the telephone compartment of a Post, P.A., No. 3, it is necessary for the lantern glass (Glass No. 68 - Amber), which is requisitioned separately, to be fitted in position immediately after the erection of the post.  Alternatively, if this is not practicable, the lantern aperture should be plugged with cotton waste or similar material.

12. Painting
The standard colours to be used for the posts are blue outside with the interior white.  The posts are issued with only a priming coat on the outside and, after erection, the exterior should be given two coats of Paint, Glossy Blue.  The interior should not need further painting, but if necessary a further coat of Enamel, White, Finish may be given.  Care should be taken that the painting does not prevent the easy removal of the screws holding the lantern on the top of the post.


13. Equipment of Posts, P.A., No. 3
Each post requires one of each of the following components:-

Telephone No. 244, minus Cord
Unit, Signalling, P.A., No. 2
Cord, Instrument, No. 7/10M, 14 in.
Lamp, General Service, ... V/60W Pearl
Lamp, General Service, ... V/150W Pearl

The voltage of the lamps should be that of the local supply.  Diagram PA 459 shows the internal connexions of the various items of equipment.  The Telephone No. 244, minus Cord should be secured to the shelf in the top compartment by means of two wood screws and connected to the block terminal on this shelf by means of the Cord, Instrument, No. 7/10M, 14 in.  The Unit, Signalling, P.A., No. 2 should be fixed in position by means of the screws provided; tapped bosses exist in the rear of the centre compartment for this purpose.  A length of Cable, P.V.C., No. 1, 4 Wire 64 ..., run via the conduit, should be used for the connexion between the signalling unit and the telephone terminal block.

14. A Protector and Fuse No. l should be fitted in the base of the post if required under the terms of PROTECTION, General, B 1002.  A length of Cable, P.V.C., No. 1, 3 Wire 64 ... should be run between the terminal block and the protector, via the conduit provided in the right hand rear of the post. Some posts may be issued with a protector already fitted, and if not required it should be recovered and used locally.  If a protector is not required, the lead-in cable should be run direct to the terminal block.

15. The internal wiring for the power supplies is provided with the post. The police authorities will arrange for the connexion of mains supply to the cut-out. If required, a meter for these supplies may be fixed to the board provided at the rear of the lower compartment. A Lamp, General Service, V/150W Pearl should be fitted in the signal lantern and a Lamp, General Service, ...V/60W Pearl in the upper compartment of the post.

16. A temporary NOT IN USE label should be attached to the post after erection and prior to the post being brought into service.

17. Locks
One Key, Lock, W is provided with each post. When a post is brought into service, the key should be handed to the police authorities. If additional keys are required, arrangements should be made to supply them under “cash sales” terms in accordance with STORES, General, K 0011.

18. Erection of kiosks
The provision and erection of kiosks is the responsibility of the police authorities.  Particulars of the dimensions of the door to the telephone compartment should be given to the police authorities so that a Glass No. 67A may be fitted.  These details should be obtained from Drawing EC 2072. In addition, the police authorities should be advised that the equipment will benefit in service by the provision of adequate ventilation in the kiosks, thus ensuring a free air-flow and avoiding trouble due to condensation.

19. Special bracket for kiosks
The lantern used for the signal lamp at a kiosk is the Lantern, P.A., No. 1.  This lantern has a flat base and it will be necessary for a suitable bracket to be provided on the kiosk for mounting the lantern.  Fixing is effected by three bolts and nuts supplied with the lantern, and the police authorities should be supplied with a copy of Diagram PA 126 (which is a dimensioned sketch of the drilling required for fixing the lantern) so that the brackets may be drilled correctly.

20. Leading-in arrangements
For kiosks the arrangements should be made during the erection of the kiosks to provide facilities for leading-in the telephone cable.  Where convenient, overhead distribution may be used for kiosks.

21. Equipment of kiosks
A typical layout of the telephone equipment fitted at a kiosk is shown on Drawing EC 2072 and the wiring connexions are given in Drawing PA 484. A complete list of items to be provided and fitted by the P.O. at each kiosk is given on Drawing EC 2072.  The police authorities will arrange for the power supply to be connected to the cut-out and are also responsible for the provision of any internal lighting that may be required.

22. Audible signals
In addition to the signal lamp, a loud-sounding bell may be fitted at both the post and kiosk.

23. Post, P.A. No. 3
A Bell No. 61A (Bell No. 61B in d.c. areas) should be fitted in the rear of the telephone compartment. It is necessary to drill and tap blind holes in the post casting to secure the bell. The Plug, Conduit, No. 2 should be removed from the tee-piece and the conduit extended round to the bell. The bell should be connected in circuit in accordance with Diagram PA 459.

24. Kiosks
If a loud-sounding external bell is required at a kiosk, a Bell No. 61A (Bell No. 61B in circuit in d.c. areas) should be fitted in a suitable position on the kiosk. This position should be as high as possible, e.g. immediately under the eaves.  The power cabling should be extended in conduit and the bell joined in accordance with Diagram PA 484.

25. An internal bell may be provided in a kiosk by connecting a Bell No. 64D in series with the line in accordance with Diagram PA 484.

Additional Information

In the late 1980,s British Telecom started to recover the Police Posts in London.  About 9 were left in situ.

These Posts had been updated and were is varied states of repair.  Some had had the mains electrics updated and in general the mains relay set had been replaced by a modern equivalent.

Click here for information of the London Police Post restoration

Last revised: March 11, 2023