Ystrad Mynach South Signal Box stands in its original location set back from the running lines south of Ystrad Mynach station, near Caerphilly. It was erected for the Rhymney Railway by McKenzie and Holland in about 1890 and is shown on the Ordnance Survey County Series 25in map of 1900. The box is set on a stone base, as specified by the Rhymney Railway ? the McKenzie & Holland type 3 design was usually built in brick or timber ? and has an unusual outdoor timber platform to support two changes in direction of the point rodding and signal wires and bring them to ground level. The box has a 45-lever GWR 5-bar vertical tappet frame of 1926 and has been refurbished to its original style. The setting of the box, high on an embankment, currently appears to be the unique survivor of a once-common south Wales practice.
Sources include: Peter Kay, Signalling Atlas and Signal Box Directory (Third Edition), Signalling Record Society, Wallasey, 2010; Network Rail, Signal Box Register (undated). For further information on the types and designs of signal boxes see: The Signalling Study Group, The Signal Box - A Pictorial History and Guide to Designs, OPC, 1986.
B.A.Malaws, RCAHMW, 21 November 2013.