Abstract - This paper gives the basis of fail-safe signalling circuits design using repeater relays, based on British Rail (BR) practice. The design, in the same location, utilizes the principle of single cutting of a repeater circuit by the contact of primary function relay instead of the double cutting principle which is applicable to other signalling systems. Safety features of repeater circuits are maintained by implementation of special demands made on the design. The most important demands are illustrated by selected examples.

Keywords - Fail-safe circuits, safety analysis, relays.