This system had protected the Cambrian Railways for many years. There was a weakness at Abermule, in that the electric tablet machines and the other block telegraph instruments were kept in the main station buildings, while the signals were worked from a separate signal box at the east end of the station, and some of the points from a ground frame at the other end of the station. Regulations specified that only the stationmaster or signalman were to work the tablet machines, but it was common for both to be occupied with duties away from the station buildings, and it became accepted practice for any member of the station staff to work them.