1. Specification for tractive armature direct current neutral-polar line relays for railway signalling. (14th July 1950) Authors: British Standards Institution, Record Type: Book Extent: 1 online resource (14 pages) View Content: Available online (eLD content is only available in our Reading Rooms) ↗
2. Specification for tractive armature direct current neutral track and line relays for railway signalling. (26th July 1950) Authors: British Standards Institution, Record Type: Book Extent: 1 online resource (12 pages) View Content: Available online (eLD content is only available in our Reading Rooms) ↗