In British, Australian, French, and Swiss

railway signalling Railway signalling (), also called railroad signaling (), is a system used to control the movement of railway traffic. Trains move on fixed rails, making them uniquely susceptible to collision. This susceptibility is exacerbated by the enormou ...

, an Annett's key is a form of

trapped-key interlocking Trapped-key interlocking utilizes locks and keys for sequential control of equipment and machinery to ensure safe operation. Trapped-key interlocks are widely used to ensure safe access to potentially live or dangerous plant or equipment in an in ...

that locks

levers A lever is a simple machine consisting of a beam or rigid rod pivoted at a fixed hinge, or ''fulcrum''. A lever is a rigid body capable of rotating on a point on itself. On the basis of the locations of fulcrum, load and effort, the lever is di ...

or other items of signalling apparatus, thereby serving as a portable form of

interlocking In railway signalling, an interlocking is an arrangement of signal apparatus that prevents conflicting movements through an arrangement of tracks such as junction (rail), junctions or crossings. The signalling appliances and Track (rail transpor ...

. The purpose is to prevent access from sidings to the running line without authority. When not in use, the key is normally held in an Annett's lock that is fixed to the lever or concerned apparatus.

History

The Annett's key takes its name from its inventor, J. E. Annett of the

London, Brighton and South Coast Railway The London, Brighton and South Coast Railway (LB&SCR; known also as the Brighton line, the Brighton Railway or the Brighton) was a railway company in the United Kingdom from 1846 to 1922. Its territory formed a rough triangle, with London at its ...

. Annett

patent A patent is a type of intellectual property that gives its owner the legal right to exclude others from making, using, or selling an invention for a limited period of time in exchange for publishing an enabling disclosure of the invention."A p ...

ed his design in 1875; in 1881 that patent was bought out by

Saxby and Farmer John Saxby (17 August 1821 – 22 April 1913) was an English engineer from Brighton, noted for his work in railway signalling and the invention of the interlocking system of points and signals. He was later a partner in the firm Saxby and Farmer ...

Operation

In British usage, the key may be held in a locked container in the signal box that can only be opened when the corresponding signal lever is turned to ''danger'' for traffic on the running line; the lever is locked in position until the key is returned. Alternatively, the key may be attached to the train staff for the section of running line containing the entrance to the siding. At manually-worked level crossings remote from signal boxes the key to the gates can only be removed for use when the signals for the running line are locked at ''danger''. In Australian usage, the key is carried on a specified locomotive.

References

{{Reflist Interlocking systems

History

Operation

See also

References