Thanks for the detail. I believe Exeter and Westbury were later than the other WR re-signalling schemes, so condition may not be so critical. But there have been problems with more recent relay interlockings too, for example Edinburgh dating from the late 70s.
Even 20 years ago when it was only 20 years or so old, wire condition was said to be very poor at Exeter.
Also, didn’t Westbury and Exeter involve quite a bit of recycled kit from the likes of OOC? Westbury certainly didn’t have a full alphabet on it’s TDs in the past.
Yes, Westbury and Exeter are 1980s PSBs. They were the last big route relay interlocking signalling schemes on the English part of Western.
With PCP rubber insulated wire, how long it lasts depends mainly on the quality when manufactured, how much heat it is subjected to over time and for cable terminations, if it was affected by the practice of using mineral oil on the terminals.
A large amount of wiring installed in the 1980s, was discovered years later to be a particularly poor batch of wire. The "bad" batches were found to be degrading far quicker than other batches. This is the "dry" type of degradation where the inner insulation gradually turns to dust. The outer insulation then goes brittle as well, and splits. If disturbed, chunks of insulation can fall off, leaving a bare metal wire. Heat speeds up this type of degradation.
The heat can be the temperature of the air overall in the relay room or location cupboard, or it can be from equipment on the rack. Wiring on the rack above say, a power supply unit or track circuit equipment, was found to be much more likely to degrade than straight runs in trunking or cable trees that were run away from equipment.
Up until about the mid 1990s (can't remember the date now), it was common practice in some areas to use light mineral oil on the terminals where internal wires and external cables are connected, to prevent corrosion. But over time, this reacts with the insulation of the wire (the oil tracks up in the wire) causing it to degrade. This is the "wet" type of degradation. The the inner insulation gradually turns to goo. The outer insulation splits. If disturbed, bits of insulation can fall off, leaving a bare metal wire. There are other causes of "wet" type of degradation, but they are less common.
It's unlikely much equipment from OOC would have been used in the building of Exeter or Westbury. Some maybe. But spares and decommissioned parts would have been made available to other areas where the same type of equipment was in use.
The TD used at the time for the new PSBs was the then new Western Region Solid State Train Describer system (SSTD). The prototype system was IIRC first used at Swindon. Then later, SSTD was installed in some of the other 1960s and 1970s Western PSBs to replace the electromechanical WRTD (Western Region Train Describer) that was unreliable.
SSTD could handle more characters than WRTD. WRTD could only have 0 to 9 in the first, third and fourth "digits", with ten letters only in the second digit. SSTD could have characters 0 to 9, L, R and B in the first, third and fourth "digits". And characters Z, A, B, C, F, E, M, O, V, X, D, G, H, J, K, L, N, P, R, S, T, U, W, Y and * in the second digit. The four digit display could also show the "_t*_" (where "_" means blank) fault code if the cable connection to it was disconnected.
The Vaughan 4M TD system was used later to replace some SSTD systems. When the SSTD system at Bristol was replaced with a Vaughan 4M system, all the spare SSTD cards and the SSTD equipment cubicles were transferred to Westbury, as their SSTD system was still in use at the time.
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