P.A. 101, 150 and 350 POLICE SYSTEMS

P 0003
Issue 1, 1939


1. General
The system provides for a central-battery type P.B.X. switchboard at police headquarters, specially adapted to provide - in addition to the normal P.B.X. equipment - equipment for the termination of party-line circuits, each of which serves a group of street call-points (normally up to three stations per circuit).  Provision is made for fitting lamp signals and/or bells at the call-points.  Telephonic communication can thus be quickly established between police headquarters, public, and police.’

2. In the course of development, various types of switchboard have been introduced.  The design of the switchboards is very similar, but the facilities afforded vary.  To facilitate reference, the Instructions relating to each type will be issued in a separately numbered series as indicated in Table 1.


Switchboard General  Description Installation Circuit Operation Maintenance
All types P 0000 - 0099 - - - 5000 - 5099
PA 101 - P 1000 - 1099 P 3000 - 3099 P 4000 - 4099 -
PA 150, 150 TD, 150 TD/ - P 1100 - 1199 P 3100 - 3199 P 4100 - 4199 -
PA 150 MP - P 1200 - 1299 P 3200 - 3299 P 4200 - 4299 -
PA 350 - P 1500 - 1 599 P 3500 - 3599 P 4500 - 4599 -

3. Diagrams
The key diagram for each type of switchboard gives a list of the circuits and diagrams used with that particular type of switchboard.  These diagrams are as shown in Table 2.



Key diagram
PA 101 PA 101
PA 150, 150 TD and 150MP PA 150
PA 350 PA 350
PA 150 TD/GW PA 1501
PA 150 TD/BM PA 1502


4. “Switchboard, PA 101”
This was the first type of switchboard to be introduced; it is now superseded by “Switchboard, PA 150 PD”.  Discrimination between police and public calls is provided. Extension of public calls to other extensions, and discrimination of incoming calling signals on the three call-points on each party-line, are not provided.  Two 2-valve amplifiers are accommodated inside the switchboard, and can be associated with either/or both operator’s telephones for answering calls from the public.

5. Call-point equipment
The call-point consists of a kiosk or pillar.  The telephone unit includes a “Telephone No. 164” for police use; the public speak into a transmitter fitted in the centre of a loudspeaker diaphragm; the loud-speaker transmits amplified speech from the operator at the switchboard to the caller.  When required, a flashing signal light is provided for attracting the attention of police officers.

6. “Switchboard, PA 150”
This switchboard superseded “Switchboard, PA..101,” but is now superseded by “Switchboard, PA 150 TD”.  Single valve amplifiers, accommodated on the top of the  switchboard, are used in association with special  cord-circuits to transmit amplified speech and also provide for extending pubic calls to special extensions.  Discriminating calling signals for the call-points on the party-lines are also provided.

7. Call-point equipment
This is similar to that for “Switchboard, PA 101,” except that the units are provided with discriminating calling facilities.

8. “Switchboard, PA 150 TD“ is arranged for ‘through dialling,’ i.e. the caller at an extension is able to dial direct through the switchboard to the public exchange; in all other respects the switchboard is similar to the PA 150.  This switchboard supersedes PA 101 and 150, and is the present standard type.

9. Call-point equipment
This is identical to that for “Switchboard, PA 150”.

10. “Switchboards, PA 150 TB“
In certain instances, due to the demand for a switchboard of large P.B.X. capacity in addition to the normal police system equipment, it has been necessary to design special types of PA 150 PD switchboards to incorporate the additional P.B.X. equipment.  These have been designated as follows:-

Glasgow City Police -  “Switchboard, PA 150 TD/GW”
Birmingham City Police -  “Switchboard, PA 150 TD/BM”

11. Call-point equipment
This is identical in all cases to that for “Switchboard, PA 150.”

12. “Switchboard, PA 150 MP”
This is similar in design to “Switchboard, PA 150 PD,” but is not provided with amplifier cord-circuits, and there is no discrimination between police and public calls.  This switchboard was designed for, and at present is used only, on the Metropolitan Police Outer Division.

13. Call-point equipment
The call-point consists of a kiosk.  The telephone unit includes a “Telephone No. 164,” and is used by both police and public.  When required, a flashing signal light is provided for calling the attention of police officers.

14. “Switchboard, PA 350“
This is a 65-line C.B. P.B.X. switchboard modified to accommodate a strip of keys and associated lamps.  Each key actuates a flashing signal at the corresponding street call-point, which returns a signal to flash the associated switchboard lamp in unison, thus giving an indication that the flashing signal is functioning correctly.  Party line working is not provided on this switchboard, each call-point being connected to an individual line.  The battery and power plant are contained in a cabinet fitted at the Police Station.  This switchboard was designed for, and at present is used only on, the Metropolitan Police Inner Divisions.

15. Call-point equipment
The call-point consists of a kiosk or pillar.  A telephone of hand-microphone type for both police and public use, and a plug-in power unit for flashing the lamp signal, are fitted.  The equipment is connected as an external extension on the switchboard.

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Last revised: September 03, 2019