scope:

INTRODUCTION:

Signalling circuits are usually designed to be earth free, which reduces the potential for wrong side failures due to earth faults. Point drive and detection circuits are at particular risk due to the close proximity of the point equipment to the running rails and ballast. RT/E/C/11600 specifies that either earth fault detection (EFD) or separate power supplies are used for point detection, and new Railway Group Standard GI/RT7017 and Guidance Note GI/GN7517 recommend separate supplies for drive and detection. However, in the absence of the yet to be issued Part C of RT/E/C/11600 there is no definitive guidance for designers on what is required as a minimum for new projects.

This TI addresses this shortcoming in the existing standards by setting out clear requirements for new projects. Provision for alterations to existing installations should generally be to the standards of the day, subject to risk assessment.