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Procedures

NPR 739 Operating mechanical interlocking machines

This document describes the procedure for operating mechanical interlocking machines

Version 3.1, 30 September 2018

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 colourFunction
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 colourMeans 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 colourMeans that signal is

Red

At STOP

Green

Not at STOP

White

Not at STOP

Operating points and signals

Qualified Worker
Warning
Warning

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.
  1. If there is a pulling list, use it to find the correct order of levers to set the intended route.
Note
Note

Do not force a lever. Too much force may damage the interlocking machine.

  1. If necessary, use blue levers to remove facing point locking.
  2. Use black levers to set points.
  3. If necessary, use blue levers to re-apply facing point locking.
  4. Use red levers to set signals.
  5. Check that points and signals are set correctly for the route.

Failure of intended route to set

Qualified Worker
  1. If points or signals do not move to the intended position, check that you are using the correct levers in the correct order.
  2. If you are qualified, adjust the connecting wire tension.
  3. Check that linkages move freely.
  4. Return the levers to their previous positions.
  5. Check that there is no obstruction in the points.
  6. If the route cannot be set, tell:
    1. a Signals Maintenance Representative
    2. the Network Controller.