Clock No. 59, 61, 63, 65, 67, 69 and 71


Issue4, 10.11.1961



1. General
This Instruction details the policy regarding the provision of a watchman supervisory service in premises occupied by P.O. staff.  The system is provided principally at large P.O. buildings for checking the times at which the watchman visits certain points in the course of his round.  Wholly mechanical tell-tale clocks have been superseded by the electromechanical system described in D 1250 and all new installations and renewals of installations should be of this latter type. Installation details are given in D 3231 and maintenance details in D 5231.

2. Responsibility
The provision and maintenance of the system is the responsibility of the R.D. (Eng. Bch.).

3. The system may be provided on the authority of the R.D.

4. Supplies
Owing to the small demand for these systems and the variety of sizes in use, system clocks are not stocked.  The sizes most frequently in demand have been coded and details of these are given in Table 1 and in the Rate Book.

5. In determining the size of the clock to be installed, the ultimate requirements of the building should be studied.  It is uneconomical to change a clock once it has been installed.

6. Contact boxes for use with supervisory systems have been coded as Box, Contact No. 1 and a stock is held by the Supplies Dept.  The box is suitable for flush or surface fixing.

7. For points in exposed positions it is necessary to provide weatherproof boxes and these can be obtained on local purchase from Gent & Co. Ltd., 47 Victoria Street, London, S.W.1, under the title of `Contact Box, Weatherproof, Catalogue Fig. 4791'.

8. Keys for use by the watchman for operating the contact boxes have been coded as Keys, Lock, S and a stock is held by the Supplies Dept.  The number of keys required depends upon the number of watch­men employed. Six keys are sufficient for most installations. It is not necessary to provide a key for each box as the keys are common to all boxes.

9. Record charts
These charts, which vary for each installation, have not been coded.  A quantity of 500 for single cylinder clocks and 1,000 for double cylinder clocks should be obtained initially with the clock.  Later supplies will be obtained by the local Inspector of Door-Keepers.

10. The duration of the record chart will depend upon (a) the accuracy required and (b) the availability of staff for changing the charts.  The space available per hour for 12, 24, 48 and 72 hour charts is approx. 3/4in., 3/8in., 3/16in, and 1/8in. respectively.
Where accuracy is important a 12 or 24 hour chart is normally provided.  Where accuracy is not important 24, 48 or 72 hour charts are used in buildings staffed for 7, 6 and 5 days respectively.

11. Wiring
The system should normally be wired in accordance with Diagram GMT 38.  Where the provision of the system involves a large amount of wiring, consideration should be given to the use of suitably-located extensions if a P.B.X. exists and it is convenient to fit the recording clock in the vicinity of the P.B.X. A Box, Contact No. 1 should be wired across each selected extension in accordance with Diagram GMT 38, via a Key No. 289B or C. With the key normal the extensions are connected to the P.B.X. and, with the key operated, the extensions are con­nected to the recording clock. Arrangements should be made for the key to be operated when the P.B.X. is closed and restored when it is reopened.

12. Power supply
A 24V primary battery com­posed of Cells, Dry, DS5 should be used except where it is more economical to provide a power lead from secondary cells required for other purposes.  In each case, a suitable resistor should be employed to reduce the operating current to the value required (see D 1250).

13. Requisitions
Requisitions for the clocks and charts should be forwarded to the Eng. Dept. (P6/1).  Arrangements will then be made with the Supplies Dept. for purchase, delivery dates being generally of the order of six months from receipt of requirements.  The advice should include the following information

  1. Type of clock (see Table 1 and the Rate Book).  (If there is no suitable clock in Table 1, give brief details of the system, number of stations required, voltage available and duration of record.)
  2. Quantity of charts required, stating whether 12, 24, 48, or 72 hour records are required and the time the record has to commence.  Stations are shown numbered 1, 2, etc.



Clocks Nos. 59 to 65 have single cylinders.
Clocks Nos. 67 to 71 have double cylinders.


P.O. Code Size (Stations) Record Duration (Hours)
Clock No. 59A 10 12
Clock No. 59B 10 24
Clock No. 59C 10 48
Clock No. 59D 10 72
Clock No. 61A 20 12
Clock No. 61B 20 24
Clock No. 61C 20 48
Clock No. 61D 20 72
Clock No. 63A 30 12
Clock No. 63B 30 24
Clock No. 63C 30 48
Clock No. 63D 30 72
Clock No. 65A 40 12
Clock No. 65B 40 24
Clock No. 65C 40 48
Clock No. 65D 40 72
Clock No. 67A 60 12
Clock No. 67B 60 24
Clock No. 67C 60 48
Clock No. 67D 60 72
Clock No. 69A 80 12
Clock No. 69B 80 24
Clock No. 69C 80 48
Clock No. 69D 80 72
Clock No. 71A 100 12
Clock No. 71B 100 24
Clock No. 71C 100 48
Clock No. 71D 100 72

Additional Information

Description - D1250
Installation - D3231
Maintenance - D5231



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