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Quainton News Archive - Quainton News No. 24 - Summer 1975
The Quainton System of Train Communication
The last News showed a mysterious looking black box alongside a tail lamp. Many members will by now have become familiar with the "Quainton System of Train Communication", others will have seen these black boxes in the cabs of our locomotives when they are working passenger trains. The system has been in use for the past two seasons and provides a means of communication between the footplate and the Guard. It also acts as an automatic alarm system in the event of the train becoming divided, and an emergency alarm for passengers.
One box is carried on the footplate of the locomotive and usually hangs on the spare lamp bracket on the rear wall of the cab. The other box hangs on a special bracket either in the Midland Brake or the guards compartment of the GN coach. All our passenger carrying rolling stock is fitted with a weatherproof plug at each end adjacent to the coupling these terminate a cable which runs the length of the vehicle. Short jumper leads fitted with screwed plugs are used to connect these sockets and thus provide a circuit throughout the train.
Each "black box" contains a relay, bell, on-off switch, push button, and three 4½ volt bell batteries. On the train the two boxes are hung in position and all the vehicles joined together by means of the jumper leads. Both boxes are switched "on", the battery in each box energises the relay inside the other box by passing current along the train. At the same time the bell is connected to the battery within its same box but through the contacts on the relay. Because the relay has already been pulled in by the current supplied by the other box, the bell does not ring. It follows then, that if the current is broken to either relay, the contacts will close and the bell will ring, powered by the battery within its own box. The push buttons are connected in the outgoing lines with contacts normally closed, when the button is pushed the current is interrupted, the relay in the other box opens and the bell rings. Thus, the push button provides a means of ringing the bell in the opposite box and also proves the operation of the circuit.
It will be seen that this system provides a means of communication between the driver and Guard through bell codes as used on the old Auto trains and at the same time an automatic alarm in the event of the train parting. In this event, the jumper lead between the two vehicles would be broken, the current being fed to both relays would be interrupted and both bells would ring continuously until the boxes are switched off. The emergency push buttons in the passenger coaches "lock on" when pushed and again interrupt the current to both boxes and ring both bells until reset.
The train working instructions require the system to be checked at each locomotive change, the current consumed by the relays is very small and the boxes remain switched on for the duration of running.
Text © Quainton Railway Society / Photographs © Quainton Railway Society or referenced photographer
Page Updated: 28 October 2017