This simplified and approximate diagram shows Princes End with the single line to Wednesbury on the left and the double track to Tipton Curve Junction (controlled by Wolverhampton PSB) on the right. Clicking on any diagram displays a higher-resolution version which can be downloaded or printed
Layout of Relay Room
Layout of relay room at Princes End
All the relay rooms on the West Midlands Resignalling were more-or-less the same size - they certainly all followed the same basic design. Whereas some of the main-line relay rooms were packed with equipment, there was plenty of spare space at Princes End, with cable terminations on one long wall, battery chargers on the other long wall and equipment in the middle of the room.
Cable Terminations
One long wall was dedicated to cable terminations for signalling, telecommunications and power cables. All cables entered the relay room underground from the concrete trough cable route outside. The signalling cables were terminated on substantial test disconnection links to facilitate tracking down faults. The other side of the disconnection links was wired via overhead cable trays to the equipment. Cables PE1 and PE6 both ran to Location Case PE2/1. Cable PE2 ran to Location Case PE2/2. Cables L1 and L2 ran to the signal box. Finally, track circuits 464 and 467 had their adjustment resistors (464TO and 467TO), fusing and links mounted on the termination panel.
Layout of Cable Termination Panels at Princes End
Relay Racks at main line relay rooms
The West Midland Resignalling introduced 'Geographical Interlocking' using pre-wired relay units each dealing with a standard signalling function such as a 'Main Signal' or a 'Single Ended Point'. These standard units were then interconnected by multicore cables plugged into plug couplers, allowing rapid replacement during fault-finding. Relay racks mounting the 'Geographical' units were normally in one or more rows away from the walls giving technicians access to both the front and rear of the racks.
Relay Rack at Princes End
Princes End was a much simpler proposition, with only a few relays to be accommodated, so the relay rack was 'free-wired' (as all relay interlockings had been prior to the adoption of 'Geographical' units). Next to the relay rack, the Standard Telephones and Cables Train Describer was housed in an equipment cubicle with hinged access doors.
Layout of relay rack at Princes End
The relays were mainly Westinghouse style 'P'. This series of miniature plug-in railway signalling relays was the immediate predecessor to the 'BR930' plug in relays still used today.
The top row of relays were for signal and miscellaneous relays. The Down colour-light starter (lever 6) needed 3 relays, plus 1 relay associated with the next signal (WN186, controlled by Wolverhampton). The Up Home 1 (lever 19) needed 6 relays. There were 4 style 'J' relays for miscellaneous functions. The second row of relays mounted 11 relays associated with track circuits. The remaining rows were unused, apart from two style 'R4' Track Feed Sets for track circuits 464 and 467.
Power
A secure Signalling Supply of 650 volts a.c. was fed throughout the area to power Location Cases and Relay Rooms. The relay room at Princes End had a 1 kVa step-down transformer to 110 volts a.c. which was distributed to various power supplies, low voltage transformers and battery chargers. The diagram below shows two 50 volt d.c. supplies, two 12 volt d.c. supplies (one with battery back-up), 12 volts a.c. (for the lamps on the illuminated diagram at Princes End) and 110 volt a.c. supplies.
Note the way in which supplies were designated. 'B' identified the positive and 'N' the negative. The nominal voltage was appended, for example 'B12' meant 12 volts positive Where there were multiple supplies with the same nominal voltage, suffixes were added such as 'N50(S)'. Alternating supplies had an 'X' added such as 'BX110'.
Power Supply Layout
The Fuse Panel for all the supplies was located on the end of the relay rack.
Layout and Allocation of Fuses
In the next instalment (here), we'll tackle some of the relay circuits.
