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Procedures

NPR 708 Using X, Y and Z keys

This document describes the procedure for using X, Y and Z keys.

Version 4.1, 30 September 2018

Description

This document describes the procedure for using X, Y and Z keys.

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Introduction

Removing an X, Y or Z key (maintenance releasing switch key) from its cabinet allows signals to clear only in the normal running-direction. It prevents bidirectional signalling in a section.

There may be up to three cabinets at a location. Removing any key is sufficient to prevent bidirectional signalling.

FIGURE 1: Z key cabinet.

Preventing bidirectional signalling in a section

Warning
Warning

Unless an X, Y or Z key is taken, protection against rail traffic approaching from both directions must be provided for worksites.

When a Qualified Worker requests authority to remove an X, Y or Z key, the Signaller asks the Network Controller to authorise the release of the key.

Qualified Worker
  1. Ask the Signaller for authority to take the X, Y or Z key for the section.
  2. Make sure the indicator light is ON.

FIGURE 2: Z key cabinet open; button and switch handle available.

  1. Push the button.
  2. Turn the releasing switch handle to FREE.
  3. Remove the key from the lock. Check that it is the correct key for the section.
  4. Secure the key.

Restoring bidirectional signalling in a section

Bidirectional signalling is possible only when all keys are in their locks.

Qualified Worker
  1. Insert the key into the correct lock and turn the key.
  2. Turn the releasing switch handle to LOCKED.
  3. Tell the Signaller that the key has been returned.
Signaller
  1. Tell the Network Controller that bidirectional working is now available.

Keeping records

Network Controllers, Signallers and Protection Officers must make a permanent record of the removal and return of X, Y and Z keys.