Power Signalling At Bristol
The relay racks were built as part of the cabin to harmonise with the general cabin surroundings, allowing for a 10% increase for future requirements. They are of the double sided type having wooden shelves and backboards, with 3/8 inch wire holes drilled to the same layout as the terminals on the tops of the relays, supported on 2 1/4 inch by 5/16 inch angle iron framework, two such racks running the length of the cabin. The uprights are spaced at 5 foot 1 inch centres, dividing the rack into bays, the last bay at the end of the rack being used for the mounting of fuses and negative bus bars, while along the bottom of the two inside racks are mounted paper insulated cable pot-ends and terminal boards. All boards were drilled with both the fixing holes and the relay wiring holes in the Railway workshops before being mounted on site, each type of relay and cable having 10% spare spaces for future requirements. This allowed for uniform planning, and the correct positioning of any additional type of relay as construction proceeded, and still allows for this procedure to be adopted for any future additions.
The low ceiling height of the relay room in the East cabin and the need for keeping incoming cables as short as possible necessitated placing the cable pot-ends and terminal boards on the ground floor.
All cable ducts were put in while the cabin was under construction, the corners being rounded to a minimum of 3 in. radius to prevent chafing when drawing in wires. Concrete ducts run between the two racks on the floors of the relay room, and in addition 6 in. x 12 in. wooden ducts, one to each bay, run between the two racks at ceiling level being jointed to a longitudinal 12 in. x 12 in. duct running down the centre between the two racks at ceiling level, directly under the duct formed by the two RSJ's supporting the locking frame. This duct carries all wires to and from the locking frame and the relay racks.
All wood used in the construction of the rack is of teak, finished with two coats of shellac.
The two sides of each rack are joined by means of insulated steel runged ladders, one being provided for each shelf of relays. The steel runged ladders are approximately I foot wide and have rungs spaced at 10 in. centres; this horizontal "ladder" construction permits of both horizontal and vertical wiring between the relays on the various shelves.
Experience has shown that this double sided open type of rack is the easiest for installation and maintenance, and facilitates the carrying out of alterations or additions.