This control replaces all the signals in a defined area to their most restrictive aspect. Back in the early days of SSI, the only way to replace a lot of signals quickly was to remove power from the SSI (via an ESOC control), thus causing all the trackside modules to time-out and go their most restrictive states. However, doing so means a loss of indications so there is no record of what actually happened trackside during the power cut. Later, SGRCs were used to achieve this in a more friendly way. Typically a SGRC will control a junction, a whole small to medium-sized station area, or part of a large station.
Last edited by GeoffM on 15/09/2016 at 03:00