Provided as a last ditch way of putting all signals back to their most restrictive aspects by literally killing the power to the interlocking. This is a drastic measure, introduced when computer-based IECCs came into existence with the fear that communications would be lost with an interlocking with no way to stop the trains. As power is lost to the interlocking, no logging takes place and no tracking of train positions takes place so when the interlocking is restarted the signaller has to determine what train is where - time consuming and not without risk.
Last edited by GeoffM on 15/09/2016 at 03:01