Track dropping boards

A rather simplistic response and incorrect!

Track dropping boards were 'wired in' to new signalling circuitry in order to simulate the movement of trains when proving the new signalling circuitry during its commissioning on the 'signalling changeover".

Dummy fuses wired out to the board were installed in relevant feed and incoming/outgoing fuse positions instead of the normal 5A and 3A glass fuses during commissioning to allow track relays to be 'dropped' by disconnection and delta track relays to be 'picked up' by false feeding.

It was custom and practice to test and prove all the external (to the IMR or relay room) wiring & circuitry in shifts prior to the commissioning changeover shift i.e. proving all the wiring to the fuse positions [testing of outside responses] and then the track dropping board(s) [larger sites would have more than one, for instance in the late 1970s two were used at Golders Green IMR on the resignalling which I worked during the changeover] would be installed.

During the changeover shift the commissioning signal engineer would test and prove all the signalling selections, tracklocks, backlocks etc by requesting the operator of the dropping board to drop 'A' for Apple, 'B' for Bertie, etc to simulate track occupancy and to pick up Delta 'A406F' for instance to simulate a train arriving at a given point, these enabling signals to be cleared, wrong road trainstops to be lowered, backlocks to be cleared, tracklocks to lock point circuits etc etc.

Basically the track dropping board was a method of allowing the signal engineer to 'play trains' without having dozens of staff on the track with shorting strips acting as individual trains. I worked dropping boards on several changeovers in the late 1970s including Barbican on the Farringdon, Barbican, Moorgate changeover which included CWL and the now infamous Wood Green changeover [replacement of signal cabin with temporary relay room remotely controlled from Arnos Grove] in which the wiring to F & G tracks had somehow become reversed in the relay room causing the first Wood Green reverser to enter the siding and 'disappear', track locking the points reverse and stacking eastbound trains back to Manor House until the failure was diagnosed and resolved. At the time the reversal had not shown up during commissioning so it appeared that the dropping board may not have been installed correctly as the ticket strip labelling on the fuse bay had been relabelled at some point prior to the changeover! (A signal installation supervisor was blamed and dropped to wireman as I recall as even though he was not the installer of the dropping board [done by day staff] he was the night supervisor responsible for pre-testing all the external circuitry to the relay room fuses.)

Following Wood Green the dropping boards were done away with and staff walked the track with shorting strips on later changeovers giving the 'outside responses on the night' which as a result made some of the bigger jobs more tedious and lengthy, for instance Cockfosters stage 1 resignalling in which 'a room full of 'track teams' were kept on hand all night but were not actually required until quite late into the shift. I recall the particular shift as being from 2200 until 1200 for myself and another colleague who were asked to come in one hour early direct to site to assist one of the installation supervisors make some preparations for the changeover.

On larger jobs track dropping boards reduced the time required to actually commission a site in a shift but on many of the smaller jobs we didn't use dropping boards at all and tended to test in the accepted manner of today by standing ready at fuse positions or relay tops to pull fuses and lift contacts as required or using a battery and clips to pick up a delta relay etc.

I have no idea what that device was but it was not a 'track dropping board'. Track circuits are tested with track shunts, basically a calibrated resistive shunt wired to a crocodile clip and held on to the running rails by hand to test a track circuit, the standard track shunt being one ohm (there are half ohm track shunts too but I never used one in my career). For delta track circuits there is a delta spread bar placed across the running rails of a delta track at 5 foot intervals on the approach side of the delta injection point to test the sensitivity/tuning of the delta circuit.

What you are describing is unknown to me although it sounds remarkably like a trainstop gauge (for checking the position and height of a trainstop relative to the running rail) .

No doubt Tom will know what you have seen if it is indeed a track circuit testing device but your description is not good enough for me to even hazard a guess.


Track dropping boards were as I said used on signalling changeovers and wired into all the track circuit fuse positions in the IMR or relay room. Each such board comprised rows of toggle switches set on the top of what might be described as a 'hostess trolley' having handles at each end and wheels to make it easy to push around, the ones I recall being painted in yellow. The boards were connected to the fuse positions by multiple plug in multicore cable looms each with a multiplug for the board end and dummy fuses at the fuse bay end, a number of such cables being used per board, these cables when coiled up were stored inside the body of the track droppng board for transportation to site. From memory (it's 32 years since I last saw one) there were four rows of toggle switches per board, each row containing some 20 switches and each switch operating an individual track or delta track circuit or indeed a TPR circuit where the track relay circuit was wholly outside the room. Green or yellow standard ticket strip was used to label the switches when the boards were installed prior to the changeover and commissioning, indeed back then it was standard procedure to temporarily label all the fuse bay fuse positions with the same ticket stock as generally the traffolyte permanent labels would not have been available until a week or several after the signalling was 'live' on many jobs.

Thanks Randomnumber, this is the bit of kit the Tube Lines Tec's were using in the depot.

As the depot has lots of Road ways, the Tec's can carry all the kit in a big white van.

Okay, thanks for the info, I did wonder if it was a new shunting device as there are even more types of track circuits around now AIUI than when I was a signal maintenance TO.

The delta shunt bars used to be a PITA, the assistants used to lean on them so hard that the knife edges became distorted more and more over time!

Deltas were being replaced with position detectors before I retired, the Northern line certainly had them and I recall one going in at Hanger Lane Junction on the Picc/District.

Track shunts and delta spreads were maintenance bread and butter and in my time I had my fair share from Cockfosters to Heathrow, Ealing Broadway and the boundary just outside Rayners Lane!

Everything changes over time as new equipment and maintenance techniques are developed. I have often wondered why track shunts have not become automated using a powered vehicle of some kind and possibly coupled with simultaneous ultrasonic scanning of rails. Lots of manpower to be saved if such could be achieved!