Petone - Control Tables

The control tables for Petone circa 1990, before 44 crossover was removed.

Petone Track Circuits

Petone Locking

Released By Relays

No Normal Reverse Normal - R Rec. Normal (N/R) Lock

1 47

2 44

6 38

8 67.68.(73 or 38).(74 or 38.44R)

10 38.44.73

14 44.73.48

17 48.MBR.(MBCR or 47)

Note: I am confused by the expression for 17 signal. It makes more sense to me if it is written as:
48.(MBR.MBCR or 47)

38 6.10.67.(74 or 44R)
68 8



47 1
48 17

48 17.77.14 47 78





67 8.38

68 8 38

73 (8 or 38).10.14.44

74 (8 or 38.44R) (38 or 44R)

77 48


Petone Route Locking

Released By

Route Locking

After Controlling Relays restored released by

No Tcs Clear Delay after TC Occ'd Locked By Tcs Clear Delay with Tcs Occ'd No
38 37. 38T:39. 40T:6T: 6AT: 74T: (44T or 44R) 6AT (60 secs) & 74T (60 secs)

44 43.44T:44T
10 10T: 39.40T 10T (60 secs) 44
47 47.48T

48 48T: 47. 48T: 77AT: 78T


Petone Control Table

No Description
Released By Track Circuits
Detects Points

Approach Locked by Track ccts Occupied Backlocked by Track ccts ccupied Approach lock rel by delay when Tcs occ'd Controls from signal ahead Remarks No

Clear Occ'd Normal Reverse N-R

1 Switchout Control Up Main

2 Switchout Control Down Main

6 Up Outer Home NS to Up Main 6T:6AT:39.40T

900T:900AT:744CT Rel by L.S. Down 900AT (60 sec) D by 10 D/H
8 Shunt from Down Main LS to Down Main occupied, Up Main (37.38T:39.40T:10T) D Only (74T w 38N)

67T 37.38T (39.40T OR 38N) 67T (60 sec) (D by 14A D/H w 38R)
10 Up Home NS to Up Main 39.40T:10T:43.44T

(900AT OR 6N):6T:6AT 39.40T 6AT (60 sec) D by 14A D/H
14AB Up Starting from Up Main NS to Up Main. 43.44T:14T:47.48T

10T :39.40T:(6AT OR 10N) 43.44T 10T (60 sec) D by 17A D/H

May show reduce to MS

D by 17B D/H

17AB Up Directing NS to Up Main 47.48T:17T:754T

43.44T:14T:(10T OR 14N) 47.48T 14T (60 sec) D by[754] D/H

MS to Branch 47.48T:78T:79T:MBR:MBCR
48 47


38 Crossover Up and Down Mains

44 Crossover Up and Down Mains

47 Points Up Main and Branch

48 Crossover Up and Down Mains

65 Down Advanced Starting from Down Main NS to Down Main 927T:927AT:853T

D by 533 D/H
66 Down Starting from Down Main NS to Down Main 991AT:927T

D by 65 D/H
67 Down Platform Starting from Down Main NS to Down Main 66T:67T:37.38T:39.40T

74T:[44T:(77T OR 74N) OR 44R] 37.38T 74T (60 sec) D by 66 D/H
68 Shunt and Down Starting from Up Main LS to Down Main 66T:67T:37.38T:39.40T

10T 37.38T:39.40T 10T (30 sec) D by 66 D/H
73 Shunt from Up Main LS to Up Main


14T 43.44T 14T (60 sec)
Last wheel replacement 73
74AB Down Directing NS to Down Main 37.38T:74T:44T

77T:77AT:(765AT OR 77N) [47.48T:78T OR 48N] : (79T OR 78N) :48T 44T: (43.44T OR 44N) 77T (60 sec) D by 67 D/H

LS to Up Main


Controlled by push button
77 Down Junction Home from Down Main NS to Down Main 44T:77T:48T:77AT

765T:765AT Released by L.S. Down 765AT (90 sec) D by 74A D/H
78AB Down Directing From Branch MS to Down Main 44T:77T:47.48T:78T:48T:77AT

WHEN OPERATED 78T:47.48T:48T 90 secs DELAY Show R only D by 74A D/H


These tables define the interlocking circa 1993. It is the same as in 2009 with the exception of 44 points (just north of the platforms) which which were removed in the late 1990s.

I have several sources of information. Over the years there have been various changes including the removal of structures, metrication and probably other minor changes. I do not have a complete copy of the handsketch. Therefore this document must be seen as a guide to the Petone interlocking logic rather than as a 100% accurate definition.

I have the following questions about these tables (with some answers):

(a) When an up train (either route) clears the junction there is a delay of about two seconds before the 47 points F light illuminates. Similarly for a down train off the branch there is a delay before the 48 points F light turns on.
  An electronic delay unit in the Normal Lock Relay circuits of 17 and 78 signals delays the operation of these relays by about two seconds. The signal NLR must be operated for the points to be free.

(b) In the locking table under "Released by relays" there are four columns:

    Normal,  Reverse,  Normal - R Rec.,   Normal (N/R) Lock

The first two are self explanatory. What do the second two mean?

    R Rec = Relay Reciprocal?
    Normal (N/R) Lock - A latched relay?

(c) In the locking table I interpret "6T:6AT:39.40T" to mean  "6 track and 6A track and 39-40 track". Is this correct?

(d) In the locking table a dot rather than a colon is used as the delimiter e.g. 8.38. Is there a difference in meaning between the dot and the colon?

(e) MBR - Magnetic Block Relay
    MBCR - Magnetic Block Proving Relay
    MBTXPR - Magnetic Block Track Repeating Relay. Normally de-energised; energised when train on circuit.

Alternatively - MBR Melling Branch Relay
     - MBCR Melling Branch Proving Relay

I do not know!

Relay MBR determines if the branch is clear. Its state is shown by the “Branch Occupied” lights on the panel. The branch is clear if:

    (47N or 47.48T clear) and 78T clear and 79T clear and MBTXPR normal and MBCR in the “Train Departed Branch” state.

MBTXPR is a rail circuit repeater.

  • A rail circuit proves the presence of a train unlike a track circuit which proves the absence of a train.
  • MBTXR proves that a train is in the section in advance of 78 signal. It ensures that a power flick or track circuit fault cannot operate MBCR and release the locking.

Relay MBCR is a latched relay with two states:

  • “Train has entered branch”
  • “Train has exited branch”

The logic of MBCR is (with 47 points reversed):

  • If 48 points are normal a train entering the branch releases the relay, which indicates the “Train Entered Branch” state.
  • If 48 points are reversed and MBTXPR is up (proving a train is in advance of 78 signal) a train leaving the branch latches the relay to the “Train Departed Branch” state.

The “Branch Occupied” lights cannot be relied on if there are any non-standard moves.
(f) What does D by D/H mean?

  • D Green relay
  • H Yellow relay

So D by 10 D/H means green if 10 signal green or yellow

(g) What does “Released by L.S. Down” mean?

This condition seems to apply when Route rather than Back locking is used. See 6 sig (38 points) And 77 sig (48 points).

(h) Approach locking & Backlocking lock the signal and so, indirectly, the points. Route locking locks the points directly.
See 48 points and 48T.
38 points use 10JR to release locking.
6 sig (38 points) and 77 sig (48 points) - back locking of signal is released by LS down and Route locking is used instead???.

Last Updated: Friday August 9 2013

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