Description
This document describes the procedure for operating mechanical interlocking machines
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Introduction
Mechanical interlocking machines in signal boxes have large levers directly connected by:
- rods to the points that they control
- cables (wires) to the signals that they control.
Interlocking is mechanical or electrical.
At some locations the levers are connected to power‑operated signals and points. On a track indicator diagram, or behind the interlocking machine, there may be lights to show:
- whether signals display PROCEED (signal repeaters)
- the position of points.
To show the correct levers to use for setting intended routes, some interlocking machines have pulling lists.
A lever may be identified by a plate showing its function.
Controls
Levers are colour coded:
| Lever colour | Function |
|---|---|
| Blue | Operates facing point locking Operates releases Closing lever for switching in or out |
Black | Sets points |
Red | Operates signals |
Indicators
Point indicator and transit lights
If present, point indicator lights show that points have operated correctly.
| Indicator colour | Means that points are |
|---|---|
White and letter N | In NORMAL position |
White and letter R | In REVERSE position |
Green or white | FREE, and can be moved |
A flashing point transit indicator light shows that the relevant points do not have detection, because:
- the points are not in position, or
- the points are changing position, or
- facing point locking is not engaged.
Signal repeater lights
If present, signal repeater lights show that signals have operated correctly.
| Light colour | Means that signal is |
|---|---|
Red | At STOP |
Green | Not at STOP |
White | Not at STOP |
Operating points and signals
Qualified Worker
The lever of a signal protecting points with mechanical interlocking only must not be returned to NORMAL before:
- rail traffic has passed completely beyond the points, or
- rail traffic has been brought to a stand before the points.
- If there is a pulling list, use it to find the correct order of levers to set the intended route.
Do not force a lever. Too much force may damage the interlocking machine.
- If necessary, use blue levers to remove facing point locking.
- Use black levers to set points.
- If necessary, use blue levers to re-apply facing point locking.
- Use red levers to set signals.
- Check that points and signals are set correctly for the route.
Failure of intended route to set
Qualified Worker
- If points or signals do not move to the intended position, check that you are using the correct levers in the correct order.
- If you are qualified, adjust the connecting wire tension.
- Check that linkages move freely.
- Return the levers to their previous positions.
- Check that there is no obstruction in the points.
- If the route cannot be set, tell:
- a Signals Maintenance Representative
- the Network Controller.