Hand Generators & Electric Locks
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By Andrew Dickinson
Hand generators were provided in all GWR and BR(WR) signal boxes that controlled motor worked points even if the signal box had a mains electricity supply. At locations where the signal box had a mains electricity supply, and this was used to work the motor points, the mains supply was converted to 110v DC through a transformer/rectifier unit. In the event of a failure of the mains supply, the signalman turned a rotary switch located above the generator, which cut out the signal box from the 110v supply and connected the generator to the outgoing circuits. In this case, the generator was used only in supply failure emergencies. Batteries were not provided as a backup as it was generally not Western practice to have such a battery.
At signal boxes where there was no mains electricity supply, the generator was used every time the signalman wanted to move the motor points.
All the equipment (generator, hand crank lock units, electric lock/circuit controllers, relays and the point machines) required for the motor worked points was manufactured by Westinghouse Brake & Signal Company. The design and the equipment remained the same (apart from a few minor modifications) from the 1930s to the early 1960s.
An example of a generator can be seen in Adrian Vaughan’s 'Signalman's Reflections' on page 158 (lower plate) and page 160 (lower plate) but in the latter partly hidden behind the lever frame. For the former, this would not have been the normal method of installation with the rear part of the machine fitted to the windowsill. I suspect space limitations forced the installers to put it there. Normally it was mounted on a steel frame and an example of this can be seen on page 154 but here it has been used for a Tyers Electric Train Token machine instead. This steel frame was a standard structure and must have been manufactured using a standard S&T Office drawing.
The hand crank lock units referred to above were mounted on two smaller steel strips (parallel to the frame) under the generator. The hand cranks were used to operate the points when the motor had failed. The hand crank lock units were provided for two main safety reasons. Firstly, to ensure that the hand crank was in a safe place where it could not be used to wind the points over without the signalman's knowledge. Secondly, to ensure that if the crank was being used by a member of staff to wind the points over, the signalman could not operate the points from the signal box when the failure was rectified, thereby causing possible injury to the member of staff from the sudden activation of the motor. Hence, a set of contacts existed inside the lock unit that cut the outgoing power to the motor when the crank was removed.
When the crank was returned to the signal box after use, it was inserted into the unit and turned through about 30°. This locked the crank in the unit and this was then secured by a pin inserted through two lugs on the unit. (One each side of the handle) and a padlock put through a hole in the pin. The crank was, therefore, secure and only certain members of staff had a key such as the signal lineman. Later, BR(WR) installations used a unit that dispensed with the pin and a pair of small curved hinged thin steel lugs were used instead. The padlock was put through a hole in these lugs to secure the crank handle.
These hand cranks and lock units were also configured in a similar manner to single line staffs and key tokens. A crank could only be used on one set of point machines and replaced in its correct lock unit. The design feature was to prevent a crank being used on another set of points, which, without the signalman's permission or knowledge, would be a dangerous situation. At Exminster, therefore, there would be two different sets of crank and lock units.
This was achieved by giving each crank a different shaped hollow end that engaged on an identically shaped projection on the motor shaft inside the point machine. The geometric shapes that I knew were square, triangular and hexagonal. The configuration was also put on the wiring diagram so that the linemen knew which unit configuration was being used for each set of points. This information would be needed quickly if a faulty lock unit or point machine had to be replaced.
If one were to look inside Exminster Signal Box, it should be possible to find where the generator frame was installed on the floor given the four holes in the floorboards. It would normally be around the top of the staircase or to the right hand side of the lever frame.
The repeaters for points 39 and 61 would probably have been mounted side-by-side on a board at the end of the block shelf rather than being installed directly above the levers themselves. This was so that the signalman would be able to see when the points had obtained 'Normal' or 'Reverse' detection when operating the generator. This was the practice at other boxes.
The quadrants for the levers working motor points would certainly have had extra notches cut into them, as described on page 4 of Newsletter No 3. The extra notches are identified as 'B' and 'D', with 'B' being nearest the normal position of the lever and 'D' being nearest the reverse. The idea of the notches is that the lever is held in position so that the electric lock is free to 'pick' when it is energised. There is a small clearance between the notch in the electric lock blade and the lock dog itself.
The operation of the motor points also follows that described in Newsletter No 3. The lock plunger was pressed and when the lock picked, the lever could be moved from Normal to the 'D' position where it was held by the lock. The generator was then used to operate the points and when Reverse detection was obtained (showing on the block shelf indicator), the lock would pick again and the lever could be moved fully to the Reverse position.
Levers controlling motor points and signals where approaching locking was provided would be fitted with locks with a circuit controller. These types of locks are referred to as combined lock and circuit controllers. The controller had copper (or brass) bands that rotated when the lever was moved. This action either made or broke circuits with the rotation of the bands, or made circuits only at certain positions of the lever such as 'B' or 'D' for point motor operation.
The electric lock fitted to the lever controlling a motor point is identified in the wiring diagrams as an NBDR lock so that at Exminster, they would have been 39(NBDR)L and 61(NBDR)L. The levers controlling signals with approach locking would be fitted with an NB lock and would have been identified at Exminster as 46(NB)L, 47(NB)L, 79(NB)L, and so on.
An example of a lever frame with quadrant notches for NB and NBDR locks can be seen on page 155 of 'Signalman's Reflections'. This ties in with page 156 (top plate) showing the signal box diagram for the same box. Here, lever 9 (signal) has a 'B' notch in the quadrant [to allow the lever to he held in a position that holds the points locked for time required by the time release] and lever 10 (points) has 'B' and 'D' notches [to allow the lever to he held in a position that holds any conflicting signals for the operation of the generator]. The frame is of the same type as Exminster.
The photograph on page 156 also shows GWR pattern brass lock plungers. It is extremely difficult to read the exact date on the diagram, but the text at the bottom of page 155 states that the new frame was installed in October 1941. This is, more-or-less, the same time as the new frame installed in Exminster. Whether Exminster had this type of plunger installed when the 1941 frame was fitted is difficult to say. I would suggest that it would have had brass plungers at that time.
In 1941 Exminster would undoubtedly have had plungers for the operation of combined electric lock and circuit controllers. These plungers would have been identified in the wiring diagrams as 39LN and 61LN ('N' being the equipment letter used for a plunger or switch) for the motor worked point levers and 46LN, 79LN, etc, for the approach locked signal levers.
Later BR(WR) installations did away with plungers for combined electric lock and circuit controllers altogether. Instead, a contact was fitted to the lock itself and this operated to pick the lock when the lever was moved about ¾" to 1" from either Normal or Reverse positions.
Thank you to Andrew Dickinson for this technical information.