Sequential Locking
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By Andrew Dickinson
SEQUENTIAL LOCKING
I would say that sequential locking was provided on the levers working the running signals at Exminster, as it was then beginning to be practice to install such a feature with a new frame or layout.Sequential locking can be provided mechanically (in the frame locking) or electrically (on the electric locks). It is far easier to do so electrically and this is achieved by wiring the feed to the coil of an electric lock on the lever working a signal through the lock dog proving contacts (LCC) of the lock on the lever working the next signal ahead of that signal. [See diagram opposite]. Details of this locking would be set out in the locking table drawing.
I believe that when electric locks were fitted to the levers working the running signals, then the sequential locking was installed electrically. At some boxes however, the only electric lock fitted to the levers was to the section signal lever(s) and so the sequential locking would be mechanical.
The GWR method of setting it out was to state that a lever (working a signal) when normal RELEASES the lever working the signal in rear. An example from Exminster (as in diagram opposite) would be:
In 1957, the BR(WR) Signal Engineer’s Office altered the method of setting out this information so that it would then read:
Click for enlargement.