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Ref NR/PS/SIG/11755Issue 1 Date December 2000

DC Track Circuits (formerly RT/E/PS/11755)

This temporary front sheet facilitates change to the new Network Rail Standards referencing nomenclature.

The Ref above will be formally allocated to this standard when it is next changed in the meantime the contents, date and issue number of this Network Rail Standard are UNCHANGED and with immediate effect it should be referred to as “(new ref) formerly (old ref)”.

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RT/E/PS/11755Issue 1

December 2000

R A I L T R A C K L I N EP R O D U C T S P E C I F I C A T I O N

DC TRACK CIRCUITS

Endorsement and Authorisation

Endorsed by:

A Simmons, Professional Head of Signalling

Accepted for Issue by:

This publication, including the dataand information relating thereto, isnot to be used, disseminated, storedin a retrieval system, reproduced,copied or adapted either in whole orin part without the express writtenpermission of RAILTRACK plc.

Published & Issued byRailtrack plcRailtrack HouseEuston SquareLONDONNW1 2EE

© 2000 RAILTRACK PLC

RT/E/PS/11755 RAILTRACK LINE PRODUCT SPECIFICATIONIssue 1December 2000

D.C. Track CircuitsPage 2 of 84

Summary

This Line Specification states the minimum requirements for d.c. track circuits.It includes life-cycle requirements from design, safety and environmentalthrough to installation, testing and maintenance.

Issue/Revision Record

Issue Date Comments1 December 2000 New Specification. The contents are based on Railway

Group Code of Practice GK/RC0755 which is to betransferred to Railtrack Line in February 2001.

Implementation

The requirements of this Specification shall apply to all d.c. track circuitssupplied for use on Railtrack controlled infrastructure on or after 3 February2001. It is not retrospective. The following document is superseded:

Superseded documentGK/RC0755, Issue 2, December 1998

Disclaimer

Railtrack Plc has used its best endeavours to ensure that the content, layout andtext of this document is accurate, complete and suitable for its stated purpose.It makes no warranties, express or implied, that compliance with the contentsof this document shall be sufficient to ensure safe systems of work oroperation. Railtrack plc will not be liable to pay compensation in respect of thecontent or subsequent use of this document for any purpose other than itsstated purpose or for any purpose other than that for which it was preparedexcept where it can be shown to have acted in bad faith or there has beenwilful default.

Supply

Paper copies of this document will be available by printing from electronic copyor, where this is not possible, may be issued on request to the DocumentController.

RAILTRACK LINE PRODUCT SPECIFICATION RT/E/PS/11755Issue 1

December 2000D.C. Track Circuits

Page 3 of 84

Contents

Page

1 INTRODUCTION........................................................................................................... 7

1.1 PURPOSE...................................................................................................................... 71.2 SCOPE........................................................................................................................... 71.3 INTRODUCTION ..................................................................................................... 7

2 APPLICATION AND CONSTRAINTS ....................................................................10

2.1 APPLICATION..........................................................................................................102.2 CONSTRAINTS........................................................................................................102.2.1 Designs for New Work .....................................................................................102.2.2 Track Circuit Length...........................................................................................102.2.3 Switches and Crossings (S&C)..........................................................................102.2.4 Point Heater Restrictions..................................................................................112.2.5 Residual Interference Voltage...........................................................................112.2.6 Lightweight Vehicles and Others Susceptible to Poor Train Shunt .........112.2.7 D.C. and Dual Electrified Areas .......................................................................122.2.8 A.C. Electrified Areas .........................................................................................122.2.9 Interfacing with Other Types of Track Circuit.............................................122.2.10 Operating Category and Interface Delay Requirements ............................13

3 FUNCTIONAL REQUIREMENTS..............................................................................14

3.1 THEORETICAL OPERATION ..............................................................................143.1.1 Non-adjustable D.C. Track Circuit .................................................................153.2 BONDING REQUIREMENTS ...............................................................................163.2.1 A.C. Electrified Lines ..........................................................................................173.2.2 Non-electrified Lines ..........................................................................................173.2.3 Track Circuit Interrupters ................................................................................173.3 ELECTRICAL STAGGER ........................................................................................183.4 COMMON RAIL BALANCE..................................................................................183.5 ALTERNATIVE CONFIGURATIONS .................................................................193.5.1 Feed End Relays TR(F)........................................................................................193.5.2 Relay End Adjustment Resistance to Increase the Sensitivity of Low

Voltage Track Circuits (not for new work) ..................................................193.5.3 Diode Track Circuit............................................................................................21

4 PHYSICAL REQUIREMENTS ......................................................................................23

4.1 FEED AND RELAY TAIL CABLE LEADS............................................................234.2 PREFERRED DESIGNS FOR NEW WORK .......................................................23



4.2.1 Standard A.C. Immune Track Circuit with Non-adjustable Feedset(Medium Voltage) ................................................................................................23

4.2.2 Standard A.C. Immune Track Circuit with Battery Standby (MediumVoltage)..................................................................................................................26

4.2.3 Diode Track Circuit (Medium Voltage)..........................................................284.3 NON-PREFERRED EXISTING DESIGNS ...........................................................304.3.1 General ..................................................................................................................304.3.2 Feed Arrangements.............................................................................................304.3.3 Relay Options.......................................................................................................314.4 FEED / RELAY COMBINATIONS ........................................................................32

5 PERFORMANCE REQUIREMENTS...........................................................................34

6 ENVIRONMENTAL REQUIREMENTS.....................................................................35

6.1 ENVIRONMENTAL CONDITIONS....................................................................356.2 IMMUNITY FROM D.C. INTERFERENCE .........................................................356.2.1 Sources of D.C. Interference ...........................................................................356.2.2 Residual Voltage Interference Levels ..............................................................426.2.3 Achieving D.C. Immunity...................................................................................436.3 IMMUNITY FROM A.C. INTERFERENCE..........................................................456.3.1 Sources of A.C. Interference............................................................................456.3.2 Achieving A.C. Immunity ...................................................................................456.4 ENVIRONMENTAL IMPACT................................................................................47

7 SAFETY REQUIREMENTS ...........................................................................................48

7.1 SYSTEM SAFETY.......................................................................................................487.1.1 Exposed Terminals..............................................................................................487.2 OCCUPATIONAL SAFETY...................................................................................487.2.1 Protective Fusing in Electrified Areas .............................................................497.2.2 Insulation of Terminals in Electrified Areas...................................................497.2.3 Safety Labelling in Electrified Areas .................................................................497.2.4 Safety Earthing......................................................................................................49

8 DESIGN REQUIREMENTS ..........................................................................................50

8.1 SPECIAL DESIGN REQUIREMENTS ...................................................................508.2 GENERIC DESIGN REQUIREMENTS .................................................................508.3 GENERIC DESIGN DELIVERABLES ....................................................................508.4 RECORDING OF DEFICIENCIES........................................................................51

9 SPECIAL INSTALLATION AND SETTING UP PROCEDURES.........................52

9.1 INTRODUCTION ...................................................................................................529.1.1 Standard A.C. Immune Track Circuit With Non-Adjustable Feedset .....529.1.2 Standard A.C. Immune Track Circuit With Charger / Cells......................52



Page 5 of 84

9.1.3 Diode Track Circuit............................................................................................529.1.4 Non-Preferred Existing Designs.......................................................................529.2 FEED END RELAY TR(F)........................................................................................529.3 STANDARD A.C. IMMUNE NON-ADJUSTABLE FEEDSET (MEDIUM

VOLTAGE).................................................................................................................539.3.1 Basic Configuration.............................................................................................539.3.2 Double Relay (without Adjustment Resistor)...............................................539.3.3 Single Relay (with Adjustment Resistor) ........................................................549.3.4 60Ω Relay..............................................................................................................549.4 STANDARD A.C. IMMUNE WITH BATTERY STANDBY (MEDIUM

VOLTAGE).................................................................................................................549.4.1 Basic Configuration.............................................................................................549.4.2 Double Relay (Without Adjustment Resistor) .............................................559.4.3 Single Relay (with Adjustment Resistor) ........................................................559.5 THE DIODE TRACK CIRCUIT (MEDIUM VOLTAGE)..................................569.6 NON-PREFERRED EXISTING DESIGNS USING BR 938 4Ω AND BS 1659

2.25Ω AND 9Ω RELAYS ........................................................................................579.6.1 General ..................................................................................................................579.6.2 Group A Feed Arrangement.............................................................................589.6.3 Group B Feed Arrangement .............................................................................589.6.4 Adjustment of the Basic Configuration ..........................................................589.6.5 Double Relay (without Adjustment Resistor)...............................................599.6.6 Single Relay (with Adjustment Resistor) ........................................................609.6.7 Double Relay (with Adjustment Resistor).....................................................609.6.8 Difficulties with Setting Up................................................................................61

10 SPECIAL TESTING PROCEDURES ...........................................................................63

10.1 RESIDUAL INTERFERENCE VOLTAGE TESTS................................................6310.2 CATHODIC PROTECTION TESTING..............................................................6410.2.1 Tests.......................................................................................................................6410.2.2 Remedial Actions.................................................................................................66

11 SPECIAL MAINTENANCE PROCEDURES .............................................................68

11.1 INTRODUCTION ...................................................................................................6811.2 IRJ TESTING..............................................................................................................6811.2.1 Introduction..........................................................................................................6811.2.2 Testing ...................................................................................................................6811.2.3 Prefabricated IRJs ................................................................................................7011.3 TRACK CIRCUIT MAINTENANCE RECORD CARDS.................................70

12 SPECIAL FAULT FINDING PROCEDURES ............................................................75

12.1 INTRODUCTION ...................................................................................................7512.2 SEQUENTIAL TESTING.........................................................................................75



12.2.1 Relay End Relay Voltage: Test T1 ....................................................................7512.2.2 Rail Voltage at the Links of the Relay End Lineside Apparatus Housing:

Test T2 ..................................................................................................................7512.2.3 Check the Feed End Relay Status (if fitted): Test T3...................................7612.2.4 Feed End Relay Voltage: Test T4......................................................................7612.2.5 Track Short or Bonding Disconnection: Test T5 (see RT/E/S/11752, Part

P) 7712.2.6 Feed End Voltage at Lineside Apparatus Housing: Test T6........................7712.2.7 Supply to Feedset: Test T7................................................................................77

12.3 RE-TESTING..............................................................................................................78

13 REFERENCES ..................................................................................................................79

14 GLOSSARY......................................................................................................................81

APPENDIX A LIST OF COMPONENTS............................................................................82

A.1 BONDING.................................................................................................................82A.1.1 Fishplate Type Bonding ......................................................................................82A.1.2 Feed & Relay Leads..............................................................................................82A.1.3 Jumper Bonding (except traction rail on electrified lines) .........................82A.1.4 Jumper Bonding (traction rail) ..........................................................................82A.2 PRIMARY CELL BATTERIES ..................................................................................83A.3 TRANSFORMER / RECTIFIER UNITS .................................................................83A.4 BATTERY CHARGERS & SECONDARY CELLS ..............................................83A.5 TRANSFORMERS.....................................................................................................83A.6 ADJUSTMENT RESISTORS....................................................................................83A.7 FUSE / DISCONNECTION LINKS ......................................................................83A.8 RELAYS .......................................................................................................................84A.9 CHOKES.....................................................................................................................84A.10 RECTIFIER TERMINATION UNITS.....................................................................84



Page 7 of 84

1 INTRODUCTION

1.1 PURPOSE

This Product Specification gives details of best practice in respect of d.c. trackcircuits in order to achieve the requirements of RT/E/S/11752.

1.2 SCOPE

The contents of this Product Specification apply to both new and existing d.c.track circuit installations, and shall be read in conjunction with RT/E/S/11752.The following types of track circuit are included:• low voltage non-immune,• low voltage a.c. immune,• medium voltage non-immune,• medium voltage a.c. immune,• medium voltage a.c. immune/d.c. tolerant,• diode.

1.3 INTRODUCTION

D.C. track circuits are the simplest, least costly and most reliable type of trackcircuit and are therefore the natural first choice for other than d.c. electrifiedareas. However, the geographical limits of each section must be defined byinsulated rail joints (IRJs) and the cost of these may influence choice towardsjointless designs, especially on main lines where the whole life cost of IRJinstallation and maintenance is a larger factor.

In the basic form of d.c. track circuit, power is applied to the rails at one end ofthe section and is transmitted via the rails to a d.c. track relay at the other endas shown in Figure 1.



TRR1 R2

RBTB

TN RN

TailCables

Feed Resistor

D.C. Power SupplyMains Rectifier

OrCharger & Battery

OrPrimary Cells

Disconnection Links Or Fuses

IRJs

Figure 1

The d.c. power supply, obtained from a mains transformer / rectifier, tricklecharged secondary battery or a primary battery, is fed through a feed resistorto the rails. The resistor is necessary to limit the current drawn from the feedunit when the track circuit is shunted by the train, and to permit the trackcircuit sensitivity to be adjusted. The performance of d.c. track circuits isdetermined by:

• the required minimum drop shunt;

• the drop away rail voltage (to tolerate d.c. interference and railcontamination);

• the minimum ballast resistance at which the track circuit remains functional;

• the need or otherwise for a.c. immunity (a.c. traction, a.c. point heater,train heating shore supply or other a.c. source induced).

Within the limitations imposed by basic operating principles and commissioningmethods, d.c. track circuit equipment can be designed to fulfil any requiredperformance. A variety of types have been used in the past and many of thesecontinue in service. In the interests of standardisation, it is necessary to limitnew installations to certain preferred options.



Page 9 of 84

When track circuits had to be powered by primary batteries, the conservationof power was of utmost importance; early designs, therefore, had low values ofeverything; feed voltage, feed resistance, rail voltage and relay resistance andoperating values. The availability of mains power led to new designs with lessemphasis on power conservation. Designs became available which required nofeed adjustment, whilst rail voltages could be raised to improve detection withpoorer vehicles and / or poorer rail surfaces. Designs were adapted to achieveimmunity to a.c. interference and to enhance tolerance to d.c. interference.



2 APPLICATION AND CONSTRAINTS

2.1 APPLICATION

The application of d.c. track circuits fulfils the basic requirement for continuoustrain detection.

Where additional integrity is required, e.g. for the operation of automatic levelcrossings (not locally monitored), they shall be used in conjunction with someother type of train detection device.

Where reduced integrity is sufficient, e.g. for the operation of automatic levelcrossings locally monitored by the train driver, certain requirements may berelaxed (see section 10.1 on Residual Interference Voltage Tests).

2.2 CONSTRAINTS

The following constraints apply to the use of d.c. track circuits, in addition tothe general restrictions given in Part F of RT/E/S/11752:

2.2.1 Designs for New Work

Only the following designs provide the required integrity for new work:• medium voltage a.c. immune,• medium voltage a.c. immune/d.c. tolerant,• diode.

2.2.2 Track Circuit Length

The maximum operational lengths are dependent upon the configuration usedand minimum ballast resistance that can be expected. In a.c. electrified areas,there are additional length restrictions to limit the traction interference.

Full details are given in section 4.

There is no special restriction on minimum length, other than that given inRT/E/S/11752.

2.2.3 Switches and Crossings (S&C)

Diode track circuits shall not be used in S&C, as they are not suitable for singlerail configuration.



Page 11 of 84

Other types of d.c. track circuit may be used in either single rail or double railmode.

2.2.4 Point Heater Restrictions

D.C. track circuits shall not be installed through S&C fitted with d.c. electricpoint heaters.

Only a.c. immune designs shall be used through S&C equipped with a.c. electricpoint heaters unless the heaters on each rail are supplied from separate isolatedpower supplies to an approved design.

2.2.5 Residual Interference Voltage

A d.c. track circuit shall not be used where the track condition is such thatresidual interference voltage presents an unacceptable hazard to trainoperations. Further details are given in section 6.2 on Immunity from D.C.Interference and in section 10, Testing Procedures.

Significant improvement may be achieved, where practicable, by the use ofdouble rail rather than single rail configuration. Where this is not practicable, afeed end relay may be introduced to obviate any restriction on use.

Where new d.c. track circuits without feed end relays are to be introduced oninsulated concrete sleepers, it is important that the general condition of thoseinsulations be verified some time before commissioning, since failure to do socould result in an inability to commission due to excessive d.c. residual voltageinterference.

For the same reason d.c. track circuits are unsuitable for use on track whichuses concrete sleepers that are not insulated from the rails, or steel sleepers.

2.2.6 Lightweight Vehicles and Others Susceptible to Poor TrainShunt

On non-electrified lines used by lightweight vehicles in Classes 14X to 16X orother modern rolling stock designated as susceptible, unless they are fitted withTrack Circuit Assisters (TCAs), the only generally permitted types are:• medium voltage a.c. immune,• medium voltage a.c. immune/d.c. tolerant,• diode.



Low voltage d.c. track circuits (see section 3.5.2) may also be used, providedthey are adjusted for high sensitivity, but only in the following circumstances:• on uni-directional lines, or• where sequential track circuit proving is provided.

However, all types of d.c. track circuit may be used where an assessment showsthat all susceptible vehicles permitted to use the line are fitted with TCAs.

2.2.7 D.C. and Dual Electrified Areas

D.C. track circuits shall not be installed on d.c. and dual electrified lines.However, the d.c. medium voltage a.c. immune/d.c. tolerant type may be usedon a.c. electrified lines in the vicinity of dual electrified lines, even if the tractionreturn systems cannot be isolated, subject to an immunisation evaluationexercise.

2.2.8 A.C. Electrified Areas

Only a.c. immune designs shall be used in a.c. electrified areas. Track circuitson a.c. electrified lines are subject to particular length restrictions (see section4.2.1.4). Diode track circuits are not A.C. immune.

a) Traction return cross bonding must be provided at all insulated rail joints(IRJs) in the traction return rail. The traction return rails in adjacentterminal platforms shall also be bonded together at the buffer stop end (seeRT/E/S/11752).

b) The traction return rail shall, wherever practicable, be positioned on thecess side to enable structure bonds to be kept short.

c) Double rail reed or TI.21 track circuits must not be allowed to besurrounded by an area of d.c. single rail track circuits, e.g. on a loop line, asdescribed in the appropriate Track Circuit Product Specification.

2.2.9 Interfacing with Other Types of Track Circuit

The relay end of a non a.c. immune d.c. track circuit is not permitted to abut aHVI track circuit. A.C. immune types are not restricted.

The relay/feed end of a diode track circuit is not permitted to abut a reed orHVI track circuit (i.e. the permitted interface is at the diode end).

No style of d.c. track circuit is permitted to abut a FS2600 track circuit, or thetransmitter end of an Aster type U or SF15 track circuit.



Page 13 of 84

There are no other special restrictions when adjoining other types of trackcircuit, apart from the need for IRJs on both rails. Since the sharing of acommon rail with other types of track circuit is thereby precluded, interfaceswithin S&C layouts are not achievable.

However, special precautions shall be taken where low voltage d.c. trackcircuits abut to higher voltage d.c. track circuits, as follows:

• Track circuits of dissimilar design shall not share a common rail.

• With double rail IRJ abutment between dissimilar d.c. track circuits, correctelectrical staggering must be achieved.

• Where the difference between their clear rail voltages can exceed the railvoltage at which the lower voltage relay can pick up, the lower voltage trackcircuit shall be fitted with a feed end relay, to guard against IRJ failure.

2.2.10 Operating Category and Interface Delay Requirements

D.C. track circuits are categorised as Operating Category B, requiring one slowto pick-up track repeat relay (TPR) in relay based signalling systems, or standardtrack circuit data in Solid State Interlocking (SSI) and the equivalent in otherdata driven systems. Reference shall be made to the appropriate part ofRT/E/S/11752 for interface delay requirements between adjacent track circuits.



3 FUNCTIONAL REQUIREMENTS

3.1 THEORETICAL OPERATION

The general operation of d.c. track circuits can be understood by reference tothe equivalent circuit shown in Figure 2.

FeedResistance Cable

Resistance

CableResistance

CableResistance

CableResistance

BallastResistance

Rail

Rail

Test BoxTrain Shunt

TR

Figure 2

At first sight, it would appear possible to design a workable d.c. track circuit ofany feed voltage whatsoever, as long as the other circuit components arechosen to complement that voltage decision. There are, however, a number ofconstraints which serve to limit design options:

a) The track is very leaky and the ballast resistance of a clear track circuit oftenforms the principal load. Higher rail voltages can only be attained at theexpense of excessive amounts of power dissipated in the ballast. Thissuggests that rail voltage must be kept as low as possible.

b) If the track circuit is to function over a wide range of ballast resistance,weather induced changes in ballast resistance should have a minimal effect onrail voltage. This suggests that the feed resistance should be as small aspossible.

c) The feed resistance limits the current drawn from the supply when the trackis occupied. If that current is to be kept low, the source voltage must alsobe kept as low as possible.

d) The minimum operating voltage at the relay must be sufficiently greater thanany d.c. interference voltage so as to avoid wrong side failures of the trackcircuit.



Page 15 of 84

e) When conducting a drop shunt test, the relay will drop away at a particularvalue of the effective resistance comprising the ballast and drop shuntresistances in parallel. Therefore, a rise in ballast resistance will reduce thevalue of the drop shunt, and vice versa.

f) For any given adjustment, a reduction in ballast resistance (e.g. in wetweather) will increase the feed current and reduce the rail voltage,ultimately resulting in a right side failure.

g) After re-adjustment to compensate for wet weather, an increase in ballastresistance as the track dries out will reduce feed current and increase railvoltage.

3.1.1 Non-adjustable D.C. Track Circuit

Reconsideration of Figure 2 shows that by specifying the relay, the maximumlead resistance and the minimum operational ballast resistance, it is possible toselect values of feedset voltage and resistance which render adjustmentunnecessary. The critical requirements are shown in Figure 3.



0.5Ω V Drop Away

Feed Set

2Ω

V Pick Up

Feed Set

2Ω

2Ω

20Ω

Relay

Feed LeadRelay Lead

Ballast

Feed Set

Relay

(a) Minimum Drop Shunt

The lowest value of drop shunt will occur when

the ballast resistance is infinite and short leads

offer zero resistance. Thus, when the minimum

drop shunt is connected across the feedset

output terminals, its terminal voltage should fall

to the minimum relay drop-away voltage. Any

finite ballast resistance will then give a higher

drop shunt.

(b) Minimum Operational BallastResistance

This occurs when both feed and relay leads

have maximum permitted resistance. Thus,

when the depicted resistive load is applied to

the feedset terminals, the relay voltage must

equate to maximum pick up.

(c) Relay Power Dissipation

Maximum power is applied to the relay when

the ballast resistance is infinite and the leads

have zero resistance. Thus, when the relay is

connected directly across the feedset

terminals, the power injected into the relay

must not exceed its design maximum.

Figure 3

Conditions (a) and (b) give simultaneous equations which can be solved to givethe required combination of feedset voltage and resistance. It is important tounderstand that the (a) / (b) solution applies to a particular design of relay, asdoes condition (c). Therefore, the non-adjustable feedset can only be operatedin conjunction with its designated relay type.

3.2 BONDING REQUIREMENTS

The limits of d.c. track circuits shall be defined by IRJs in at least one rail. Insingle rail mode, IRJs are provided in the insulated rail. In double rail mode, IRJsare provided in both rails. General details of bonding arrangements arecontained in Part F of RT/E/S/11752, the following being applicable to d.c. trackcircuits:



Page 17 of 84

3.2.1 A.C. Electrified Lines

Single rail configuration shall be used, implemented with Standard seriesbonding on the insulated rail and parallel Yellow traction bonding on thecommon rail (i.e. the traction return rail). In this mode, it shall be acceptedthat the traction rail bonding precludes detection of rail breakage in thecommon rail. The special requirements for long spurs are given inRT/E/S/11752, Part F, section 4.5.3.

3.2.2 Non-electrified Lines

The preferred configuration is double rail, implemented with Standard seriesbonding on both rails.

Only where the double rail configuration is impractical, generally at S&C (unlessC&P, etc.), the single rail mode may be used. This shall preferably beimplemented with Standard series bonding on both rails, although in complexS&C the common rail may need to be parallel bonded. The series bonded railsshall be fitted with Standard bonding and only the parallel bonded rail withYellow Standard bonding. The special requirements for long spurs are given inRT/E/S/11752, Part F, section 4.5.3. In parallel bonded mode, it shall beaccepted that the bonding precludes detection of rail breakage in the commonrail.

Any proposal to convert series bonding to parallel bonding (i.e. to add Yellowbonding), perhaps to improve a residual voltage problem, shall consider thesafety implications of loosing broken rail detection.

3.2.3 Track Circuit Interrupters

Track circuit interrupters may be wired in series with d.c. track circuit bonding,subject to all the following conditions:

a) The interrupter bonding carries no traction current.b) The interrupter bonding is of the opposite polarity to that of the rail on

which the interrupter is situated, to prevent a wrong side failure frominsulation breakdown (or contact with the rail after operation).

c) The interrupter is cut into the relay end of the track circuit rather than thefeed end, to prevent any residual voltage holding up the track relay if theinterrupter were struck.

d) All signals reading over the track circuit concerned are, where practicable,replaced by the track circuit becoming occupied.



e) The operation of the one track circuit, where practicable, places ormaintains at danger the necessary signals on all the adjacent lines.

Where it is not practicable to fulfil conditions d) and e), e.g. in the case ofmechanically operated signals, the signals concerned shall be prevented fromclearing when the track circuit associated with the interrupter is occupied.

If any of the above conditions are not fulfilled, the interrupter shall instead beprovided with its own track circuit interrupter relay, which, in turn, is cut intothe TPR circuit.

The general requirements for the installation and use of track circuitinterrupters are contained in RT/E/S/11764.

3.3 ELECTRICAL STAGGER

The bonding layout shall be arranged so that a change of electrical polarityacross all IRJs is created, the intention being that a failure of the IRJ will notcreate a potential wrong side failure due to the feed of one interfering with therelay of the other. The opposing voltages are meant to cancel out with theresult that both track circuits fail right side.

However, where this cannot be achieved, lack of change of electrical polarityacross an IRJ is permitted where the feed end of adjacent track circuits abut. Inthis case, the two track circuits concerned shall be of the same type and power.Any lack of correct staggering shall be recorded on the bonding plan.

Where neither polarity stagger or feed end abutment can be arranged, bothtrack circuits shall be fitted with feed end relays.

It should be appreciated that if one track circuit has a significantly higher railvoltage than its neighbour (e.g. a BR867 and a low voltage type), the IRJ failurepermits the higher voltage track circuit to swamp its neighbour. Both trackcircuits continue to function although the low voltage relay is operating withopposite polarity to that normally applied by its legitimate feed. The lowvoltage track circuit is then at risk of wrong side failure due to a single bondingdisconnection.

3.4 COMMON RAIL BALANCE

Where a group of track circuits share a common rail, it is necessary to achievean approximate balance whereby the aggregate current flowing from thecommon rail into the ballast approaches zero.



Page 19 of 84

The requirement for electrical stagger tends to also fulfil the requirement forcommon rail balance, provided that all track circuits are of similar voltage /power characteristics. However, where there is a conflict, other bondingsafety rules take precedence over balancing the common rail.

3.5 ALTERNATIVE CONFIGURATIONS

3.5.1 Feed End Relays TR(F)

Within reasonable limits, d.c. interference on a d.c. track circuit does not causea malfunction provided that the bonding remains intact. It may, however, causea wrong side failure when a single bonding disconnection occurs.

If a second track relay is separately connected across the rails at the feed end,the ability of a bonding disconnection to cause that unsafe failure is eliminated.Whilst a feed end relay can be applied to any d.c. track circuit variant, theadditional load imposes a reduction in maximum permitted length and reducesthe life of primary cells where fitted.

Where such a relay is fitted, the following shall apply:

• The feed end relay shall be to the same specification as the track relay (TR).

• The feed end relay shall be connected across the rails at the same positionas the feed, although its connections to rail shall be independent of thoseused for the feed.

• Both relays shall independently control the track repeat relay (TPR) or, inthe case of Solid State Interlocking (SSI) schemes, return separately to theinterlocking and be combined in the data.

• There shall never be more than two track relays on one track circuit.

3.5.2 Relay End Adjustment Resistance to Increase the Sensitivityof Low Voltage Track Circuits (not for new work)

As explained in Part F of RT/E/S/11752, the ability to detect vehicles on poorrail surfaces is related to the rail voltage at which the relay drops away.

Inserting additional resistance in series with a track relay will raise the railvoltage at which it operates and therefore reduce the significance of anyinterference voltages present across the rails. The legitimate power fed intothe track circuit will, however, have to be increased, thus imposing a reductionin maximum permitted length.



Older designs of track circuit using such as the BS 1659 (9Ω) shelf type or BR938 (4Ω) plug-in relay directly across the rails, operate at a drop-away railvoltage below 0.3V and are therefore susceptible to loss of trainshunt underadverse conditions. They are classified as “low voltage”.

Low voltage d.c. track circuits can have their poor trainshunt characteristicsimproved by insertion of additional resistance in series with the relay, as shownin Figure 4. The rail voltage at relay drop-away is increased in sympathy with theratio of total resistance to relay resistance.

V Relay

V Rail

Added Resistance

Figure 4

Inserting such a resistance raises the minimum operational ballast resistanceunless more power is fed to the track. This is done by first reducing the feedresistance to a point where the feed arrangement is supplying its maximumrated current during track occupied short circuit conditions; the relay endresistance is then set to a maximum, consistent with reliable operation.

The extent of sensitivity improvement achievable by this method is limited bythe output power available from the particular design of feed arrangement.Similar performance to the medium voltage relay types will not be attainedunless a value of additional resistance at least equal to the relay resistance itselfis achievable.

Note: The a.c. immune track relays to BR 939 (20Ω), BR 966 F2 (9Ω) and BR966 F9 (60Ω) have drop-away values in excess of 0.7V, and have been found tooperate satisfactorily under the degree of contamination typically experiencedon running lines. They are classified as “medium voltage”.

Note: Track circuits using the BS 1659 (2.25Ω) relay are incapable ofimprovement in this manner.



Page 21 of 84

3.5.3 Diode Track Circuit

In this design, both relay and feed are located at one end of the track circuitwhilst a diode is placed across the rails at the opposite end, as shown in Figure5. Although the design uses an a.c. immune relay, the track circuit itself is nota.c. immune and can only be used in non-electrified areas. It requires an a.c.power supply, making it more difficult to provide a standby. Its use is usuallyrestricted to level crossing controls in rural areas, where the avoidance oflineside power distribution away from the crossing presents a significant saving.

TR

A.C. Immune Relay

Figure 5

Power is supplied to the rails via a transformer and series adjustable feedresistance with a BR 966 F2 a.c. immune track relay connected across the feedleads.

With an open circuit diode or any other disconnection, an a.c. waveform ispresent on both rails / relay and the relay remains de-energised (see Figure 6).

On connection, the diode presents a near short circuit to alternate half cycles,increasing the feed instantaneous current and volt drop across the feedresistance. Thus, the rails and relay are presented with a half wave rectifiedwaveform to which the relay responds.

The presence of a train or a short circuit failure of the diode, short circuits therelay and causes the feed power to be dissipated in the feed resistance.



Relay Voltage

Diode Connected

Diode Disconnected

Figure 6

Note: The relay of the Diode Track Circuit does not count as a Feed EndRelay, and a Feed End Relay cannot be incorporated into this design.



Page 23 of 84

4 PHYSICAL REQUIREMENTS

4.1 FEED AND RELAY TAIL CABLE LEADS

All leads shall be single 2.5mm² flexible cable terminated to the rail with amoulded rubber connection; the leads may be duplicated for reliability. Adisconnection box may also be utilised. If a disconnection box is used, only onetrack circuit may be terminated within each box. For duplicated leads, it isadvisable to use a disconnection box as its use will enable continuity to the railand renewal of cables to be accomplished without disconnection of the trackcircuit. A separate twin cable shall be provided from each track circuitdisconnection box to the lineside apparatus housing or equipment building.

Track circuit leads are to be terminated on disconnection links at the linesideapparatus housing (using fully insulated BS 88 type carriers in electrified areas).The carriers shall be fitted with solid links, except for the insulated rail of singlerail track circuits in electrified areas, which shall be fitted with 6A fuses to BS88.

The loop resistances of tail cable leads between rail and lineside apparatushousing are not critical, although values greater than 2Ω will progressivelydegrade performance.

4.2 PREFERRED DESIGNS FOR NEW WORK

4.2.1 Standard A.C. Immune Track Circuit with Non-adjustableFeedset (Medium Voltage)

This track circuit uses the BR 867 feedset, which incorporates a feed resistorintegral within a choke provided to achieve a.c. immunity. It shall be fed from asecure 110V 50Hz power supply and can be used in a number of different relayconfigurations as follows:

4.2.1.1 Basic Configuration

• See Figure 8

• Uses a single track relay complying with BR 939 20Ω

• Earlier installations used the BR 966 F2 9Ω relay but this shall not be usedfor future work, except where essential to retain design uniformity.



4.2.1.2 Basic & Feed End Relay

• See Figure 9

• An additional relay at the feed end obviates the need to comply with theresidual interference voltage limitations.

• Both feed and relay end relays shall be of the same type.

4.2.1.3 Basic & Relay Adjustable Resistor

• See Figure 10

• BR 3000 Appendix 2 adjustable resistor in series with the relay improvestolerance to residual interference voltage as well as improving detectionwith poor vehicles and / or surfaces.

4.2.1.4 Basic (substituting 60Ω Relay)

• See Figure 8

• BR 966 F9 60Ω relay improves tolerance to d.c. traction interference.

• Useful on a.c. lines where d.c. interference is marginal.

• The rail voltage of all configurations is adequate for the detection of Class14X - 16X lightweight vehicles.

• The maximum operational lengths are dependent upon the configurationused and minimum ballast resistance that can be expected as shown inFigure 7.

Configuration Length (Timber) Length (Concrete)

9Ω TR only9Ω TR & Feed End Relay9Ω TR & Relay Adj. Resistor

700 metres500 metres350 metres





60Ω TR only 250 metres 350 metres

Figure 7



Page 25 of 84

Note: Where d.c. track circuits are fitted to a.c. electrified lines, additionallength restrictions which limit the traction interference are applicable:

• Track circuits using 20Ω relays to BR 939, are to be a maximum of 1000min length.

• Track circuits using 9Ω relays to BR 966 F2, are to be a maximum of 680min length.

• Track circuits using any other type of track relay, are to be a maximum of600m in length.

These limits will require reassessment where new types of rolling stock areintroduced.

Prioritisation of retrospective action shall be on the basis of exposure to riskfrom transformer inrush currents or poor traction current collection due tohigh speed running or overhead line conditions (see section 6.2 on Immunityfrom D.C. Interference).

However, on main lines where the track has been well maintained and this canbe foreseen to continue, it may be possible to operate track circuits overgreater distances. In a.c. electrified areas, any such length extension shall also becompatible with traction interference requirements.

TR

TB

TN

RB

RN

R1 R2BX TB

NX TNL9R 20R S

Figure 8



TR

TB

TN

RB

RN

R1 R2

TR(F)

R2 R1

RBF

RNF

BX TB

NX TNL9R 20R S

Figure 9

TR

TB

TN

RB

RN

R1 R2BX TB

NX TNL9R 20R S

Figure 10

Note: In a.c. electrified areas, the links in the insulated rail legs are replacedwith 6A fuses (type TIA6).

4.2.2 Standard A.C. Immune Track Circuit with Battery Standby (MediumVoltage)

This design uses the BR 939 20Ω relay but with a 12V battery charger / cells forthe power supply. The same choke as fitted to the BR 867 feedset is used fora.c. immunity together with a BR 3000 Appendix 1 adjustable feed resistor.

It is suitable in non-electrified areas without secure power supply, eithergenerally or where there is a localised risk of a.c. interference caused by pointheaters or shore supplies for carriage heating.

4.2.2.1 Basic Configuration

• See Figure 12

• Uses a single track relay complying with BR 939 20Ω.



Page 27 of 84

4.2.2.2 Basic & Feed End Relay

• See Figure 13

• An additional relay at the feed end obviates the need to comply with theresidual interference voltage limitations.

• Both feed and relay end relays shall be of the same type.

4.2.2.3 Basic & Relay Adjustment Resistor

• See Figure 14

• BR 3000 Appendix 2 adjustable resistor in series with the relay improvestolerance to residual interference voltage as well as improving detectionwith light vehicles and / or contaminated surfaces.

• The rail voltage is adequate for the detection of lightweight Class 14X - 16Xrail vehicles.

• The following maximum operational lengths are dependent upon theconfiguration used and minimum ballast resistance that can be expected asshown in Figure 11.

Configuration Length (Timber) Length (Concrete)




Figure 11

Note: Where d.c. track circuits are fitted in a.c. electrified areas, additionallength restrictions which limit the traction interference, are applicable. Seenote below Figure 7.

However, on main lines where the track has been well maintained and this canbe foreseen to continue, it may be possible to operate track circuits overgreater distances. In a.c. electrified areas, any such length extension shall alsobe compatible with traction interference requirements.



TRBX B

NX N

TB

TN

RB

RN

R1 R2

Figure 12

TR

TB

TN

RB

RN

R1 R2TR(F)

R2 R1

RBF

RNF

BX B

NX N

Figure 13

TR

TB

TN

RB

RN

R1 R2BX B

NX N

Figure 14

Note: In a.c. electrified areas, the links in the insulated rail legs are replacedwith 6A fuses (type TIA6).

4.2.3 Diode Track Circuit (Medium Voltage)

This track circuit uses a BR 966 F2 relay and requires a secure power supply. Ithas the advantage of not requiring any power supply at the end remote fromthe relay / feed, as shown in Figure 15. Despite using an a.c. immune relay, it isnot itself a.c. immune and shall only be used in non-electrified areas.

The maximum operational length is 1000 metres.



Page 29 of 84

The rail voltage is adequate for detection of lightweight Class 14X - 16X railvehicles.

This track circuit is not suitable for fitting either feed end relays or additionalrelay resistors.

TRAC immune

BX

NX

Figure 15

The diode track circuit is usually restricted to level crossing applications in ruralareas. When used in this manner, the diode is mounted in a termination unitwith a 5 way termination block. The wiring for a typical arrangement usingtreadles to disconnect the diode is shown in Figure 16. The treadles shall bemounted within the track circuit, 3m from the IRJ. Treadle 1 shall be mountedon the left hand rail and treadle 2 on the right hand rail when looking into thetrack circuit.

H1

Treadle 1

1

TNX (2)

4 x 1c2.5 mm²

(f) type C1

TO RAILS

2c 2.5 mm² (f) type C2

Treadle 2

2

1

)

)

)

)

)

(

(

(

(NX

1

BX

2

3

5

4TBX (2)

1

2

2c 2.5 mm² (f) type C2Rail Termination Unit

H1

B1

1

TBX (1)

TNX (1)

()(

B1

Figure 16

Old type termination units with only terminals 1 and 2 can be replaced with thenew unit by putting the track circuit leads directly onto terminals 1 and 2respectively as shown on the existing wiring diagram, leaving terminals 3 to 5unused.



4.3 NON-PREFERRED EXISTING DESIGNS

4.3.1 General

These designs exist in large numbers throughout the network. In their basicform, without additional resistance in series with the relay, these track circuitsare classified as low voltage. They are not suitable for the reliable detection oflightweight Class 14X - 16X rail vehicles, unless fitted with TCAs.

The addition of a relay end resistance accompanied by “high performance”commissioning can improve these track circuits, but such action is limited bythe power output available from the feed arrangement, especially on longertrack circuits.

They can also be modified by the addition of feed end relays to obviate residualinterference voltage limitations. Such modifications also have an effect onmaximum operational length and depend upon the power output capability ofthe feed arrangement.

They shall not be installed on new work, except where relatively minoralterations are involved and more extensive replacement would not beeconomically justified.

The designs have evolved from a mix / match of four feed arrangements andthree relays, although not all permutations are viable. The general arrangementis shown in Figure 17.

TR

TB

TN

RB

RN

R1 R2TR(F)

R1 R2

RBF

RNF

Optional Optional

Figure 17

4.3.2 Feed Arrangements

The four feed arrangements can be placed into two groups for mix / matchpurposes with the relays:



Page 31 of 84

4.3.2.1 Group A Feed Arrangement

This group comprises feeds with a source voltage of less than 2 volts:• Two CS2 primary cells in parallel;• Battery charger with one NiCad cell.

Track circuits with this feed arrangement cannot be sufficiently improved byinsertion of adjustable resistance in series with the relay. They are not suitablefor the detection of Class 14X - 16X lightweight vehicles, unless fitted withTCAs.

4.3.2.2 Group B Feed Arrangement

This group comprises feeds with a source voltage in the range 2 - 3 volts:• Two CS2 primary cells in series.• Battery charger with one lead-acid cell.

Such track circuits have sufficient power to enable high sensitivity adjustment toachieve acceptable operation with Class 14X - 16X lightweight vehicles notfitted with TCAs (but this is only permitted on uni-directional lines or wheresequential track circuit proving is in use).

4.3.3 Relay Options

Note: Where d.c. track circuits are fitted in a.c. electrified areas, additionallength restrictions which limit the traction interference, are applicable. Seenote below Figure 7.

4.3.3.1 BR 938 4Ω Plug-In RelayThis relay is not viable with a Group A feed under any configuration. Theperformance of this type of relay is particularly sensitive to relay end leadresistance and the figures quoted in Figure 18 for Group B feeds assume thoseleads may have a resistance up to 2Ω. Provided that the resistance is keptbelow 1Ω, the lengths quoted may be increased by up to 50%.

Feed Configuration Length(Timber)

Length(Concrete)

Group BGroup BGroup BGroup B

One TR onlyTwo TRsOne TR with Series ResistorTwo TRs with Series Resistor

400 metres200 metres300 metresNot Viable

600 metres300 metres450 metresNot Viable

Figure 18



4.3.3.2 Older Styles of Plug-In RelayOlder styles of plug-in relay may be found in use, but the performance of thesetypes of relay is not well documented. Any proposed changes shall be assessedon an individual basis.

4.3.3.3 BS 1659 2.25Ω Shelf Type RelayExisting low voltage track circuits using this relay are in the “barred” categoryfor Class 14X - 16X lightweight vehicles not fitted with TCAs, and are incapableof improvement. Further examples with this type of relay shall not be installed.As a minimum, the relay shall be upgraded to a BS 1659 9Ω shelf type. Where2.25Ω coils consist of two 4.5Ω coils wired in parallel, conversion to a 9Ω relaymay be achieved by rewiring the coils in series.

4.3.3.4 BS 1659 9Ω Shelf Type Relay

Feed Configuration Length(Timber)

Length(Concrete)

Group AGroup AGroup AGroup A


500 metres400 metresNot ViableNot Viable

800 metres600 metresNot ViableNot Viable

Group BGroup BGroup BGroup B


800 metres700 metres450 metres350 metres

1200 metres1000 metres700 metres500 metres

Figure 19

4.4 FEED / RELAY COMBINATIONS

Figure 20 briefly shows all permutations of track feed and relays, and whichcombinations shall be used for new works. For more detailed explanations oftheir uses refer to the preceding parts.

TRACKFEED

RELAYSTYLE

BR 9384Ω

BR 93920Ω

BR 966 F29Ω

BR 966 F960Ω

BS16599Ω

OPTIONS 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4

BR 867 track feedset 10V - - - - A A A - B B B - A - - - - - - -

BR 865 track feedset 6V C - - - C - - - C - - - - - - - - - - -



Page 33 of 84

BR 865 track feedset 2V C - - - C - - - C - - - - - - - - - - -

Two primary cellsin parallel 1.5V - - - - - - - - - - - - - - - - C C - -

Two primary cellsin series 3V C C C - - - - - - - - - - - - - C C C -

Charger & oneNiCad cell 1.2V - - - - - - - - - - - - - - - - C C - -

Charger & one leadacid cell 2V C C C - - - - - - - - - - - - - C C C C

Charger & 6 lead acidcell or 9 NiCad cells 12V - - - - A A A - - - - - - - - - - - - -

Diode trackcircuit design

- - - - C - - - A - - - - - - - - - - -

Options: 1: one track relay only Usage: A: use for new work

2: two track relays B: use where essential to retainuniformity in design

3: one track relay with seriesresistor

C: non-preferred existing design

4: two track relays with seriesresistor

-: not viable

Figure 20

Note: Certain combinations using a BS 1659 2.25Ω relay exist, but shall beupgraded whenever any change takes place (including a relay change).



5 PERFORMANCE REQUIREMENTS

The types of d.c. track circuit specified for new work are simple and reliable,provided that due care is taken in using the appropriate variants in eachparticular case.



Page 35 of 84

6 ENVIRONMENTAL REQUIREMENTS

6.1 ENVIRONMENTAL CONDITIONS

All equipment associated with d.c. track circuits shall conform to specificationBR967, category D, and, in addition, track-mounted equipment shall conform toBR967, category F.

6.2 IMMUNITY FROM D.C. INTERFERENCE

6.2.1 Sources of D.C. Interference

6.2.1.1 D.C. Electric Traction Systems

D.C. track circuits are not permitted on d.c. electrified lines and, since a bufferzone of IRJs is provided between such lines and non-electrified lines, d.c.traction induced interference normally only exists on a.c. electrified lines closeto areas of dual electrification (see Part F of RT/E/S/11752). Due to the lowd.c. resistance of rail, d.c. traction current injection into the a.c. electrified linescan extend for many kilometres.

Consider the single rail d.c. track circuit, depicted in Figure 21, in conditionswhere d.c. traction current is flowing in the traction return rail. The flow ofd.c. traction current along the return rail will cause a longitudinal d.c. voltagedrop along the length of that rail, the value being proportional to the value oftraction current and the length of the rail. When a train occupies the feed endof the track circuit, that longitudinal voltage appears across the track relay.

V

TR

Traction Current (I)

Figure 21



6.2.1.2 A.C. Electric Traction Systems

Whilst electric traction currents in a.c. electrification systems arepredominantly at 50Hz and harmonics of 50Hz (against which a.c. immune trackrelays are protected), they may contain asymmetric transients, very lowfrequency currents or d.c. offsets, which if of sufficient magnitude can result inwrong side failure of the track circuit.

The most well known cause of d.c. interference contained within the a.c.traction current is that due to transformer inrush on rolling stock, which isexperienced every time the unit connects to the overhead line supply. Thishappens regularly where trains pass through neutral sections, but can alsooccur after protective circuit breakers operate on rolling stock and aresubsequently re-closed. Other switching transients on the supply itself, orwithin the traction and auxiliary control systems of rolling stock, can alsointroduce asymmetric transients into the a.c. traction return current, althoughthese are typically less significant than transformer inrush.

Whilst the operate delay (400ms minimum), due to the use of slow operatingrepeat relays (to BR933), is generally sufficient to cope with transientinterference, under extreme circumstances wrong side failure of the trackcircuit can still occur.

Modern traction units employing active control methods (such as three phasedrives) can actively generate currents at a wide range of frequencies andsuperimpose them onto the traction supply. Whilst the traction controlsystems can be designed so as to avoid, as far as possible, the generation of d.c.or very low frequency currents to which a track relay could respond, some d.c.interference can be produced.

A d.c. offset on the traction supply voltage can be caused by the rectificationeffect of poor current collection between the overhead catenary and thepantograph of a train. Whilst this can be minimised by design of the overheadline, pantograph and the materials used, a small level of d.c. offset can beexpected under high speed operation, or poor overhead line conditions such asicing.

Parallel tracks are cross-bonded at regular intervals, such that the tractionreturn current from an individual train will have a number of different parallelpaths back to the feeder station. This minimises the impedance to the tractionsupply and hence the volt drop, whilst it also limits the proportion ofinterference current which can flow through an individual track circuit.However, under some circumstances, the vast majority of current from anindividual train will pass through a track circuit.



Page 37 of 84

As described above in section 6.2.1.1, and shown in Figure 21, the tractioncurrent flowing through a rail can develop a voltage across the track relay,when a train shunt is at the feed end of the track circuit, which is proportionalto the current, the track circuit length and the impedance of the rail. D.C.,very low frequency currents and asymmetric transients within the tractionreturn current can therefore result in interference being applied across thetrack relay. The primary protection is to limit the length of the track circuit(see Figure 7).

6.2.1.3 Cathodic Protection Systems

Any buried metal object, such as a pipe, tends to form one pole of a simpleprimary cell, with the surrounding soil acting as the electrolyte. A current thenflows from the pipe into the ground, causing the pipe to corrode. To preventthis, a Cathodic Protection System must be installed. To do this, an oppositepotential is applied to the pipe and ground from an external d.c. source (usuallya transformer / rectifier unit) via a buried electrode known as a ground bed(see Figure 22).

Cathodic protection is used to protect buried structures, usually pipelines,from corrosion. Any protection system found to be necessary is provided bythe owner of the buried structure or pipeline and is required to comply with BS7361-1. The procedures to be adopted are given in EHQ/PR/S/004. For detailsof the associated risks, see Railway Group Standard GL/RT1253.

Pipe Line

Ground Bed Site

Figure 22

If a railway runs adjacent to the ground bed and passes over a protectedpipeline, the rails may provide a lower resistance path for the positiveprotection current and a potential will appear down the rail, causinginterference (see Figure 23).



Railway Line

Pipe Line

Ground Bed Site

Figure 23

Since Cathodic Protection Systems are supplied by a d.c. source, they will onlyaffect d.c. track circuits.

The effect of the system is that the positive protection current enters theground on the ground bed side of the IRJ and re-enters the rails on the pipelineside.

The current flow in each rail is generally of the same order, but in single railtrack circuits, or in a double rail track circuit with a defective IRJ, there is a fargreater difference.

Any imbalance between the rails will flow via the track relay coil and can besufficient to maintain the relay energised whilst the track circuit feed isdisconnected. However, if a track relay (or associated wiring) develops anearth fault then the relay coil becomes the lowest resistance path to earth andthe relay could remain energised with the track occupied (see Figure 24).

IRJ

IRJ

TR

Rail

Rail

Train Interfering EarthCurrents Entering Rails

Pipeline

Figure 24

It can be seen from the above that the worst case occurs when the relay end ofthe track circuit coincides with the crossing point of the pipeline.



Page 39 of 84

6.2.1.4 Concrete Sleeper “Batteries”

Experience has shown that a damp reinforced concrete sleeper will behaverather like an electro-chemical secondary cell if subjected to a standing d.c.voltage. The cell charges to suit the prevailing polarity and its discharge voltageis generally in the order of 20 - 30% of the charging voltage. Whilst theampere-hour capacity of a single sleeper is very low, there are a large numberof such cells in parallel on concrete sleepered track. Experience to date hasshown this battery effect capable of maintaining a track relay energised for upto 30 minutes after the legitimate feed has been disconnected.

As the “battery” voltage is proportional to the standing clear voltage on thetrack circuit whilst the safety classification of that interference is related to therelay drop-away rail voltage, the problem is magnified by over-energisation ofthe track circuit. Non-adjustable track circuits are designed to operate withhigh energisation levels, making them particularly prone to this form ofinterference, which can be observed by disconnecting the legitimate track feedand noting the residual voltage remaining across the relay.

The condition is not unsafe provided that the bonding remains intact, since thetrainshunt is effective on both the legitimate and extraneous feeds. A bondingdisconnection may, however, cause failure to detect a train on the feed side ofthe disconnection until the extraneous capacity is exhausted.

Modern concrete sleepers are fitted with insulation between rail and sleeper;appearance of this battery effect on these types of sleepers is thereforeindicative of degradation of that insulation. The ability of non-adjustable trackcircuits to function down to low values of ballast resistance usually causesresidual voltage problems to appear long before matters deteriorate sufficientlyto actually fail the track circuit via low ballast resistance.

Many old patterns of concrete sleeper, usually associated with chaired bullheadtrack, do not provide any insulation between rail and sleeper. They aregenerally found on rural lines where few track circuits were historicallyprovided. D.C. track circuits are not suitable for such sleepered track.

6.2.1.5 Mutual Interference

Where a number of d.c. track circuits are connected together by a commonrail, the track relays are unable to discriminate between their own feed andthose of other track circuits, and a degree of mutual interference betweenthem is inevitable. This condition may be introduced by design (single rail trackcircuits) or by failure (IRJ failure of double rail track circuit).



Consider the example of two d.c. single rail track circuits. Figure 25 shows theequivalent circuit in track circuit type format whilst Figure 26 converts this to astandard electrical format for easier presentation of cause and effect. WhereVFB feed supply is disconnected, a voltage will appear across RRB as a result ofVFA, its value depending on circuit parameters.

In non-electrified areas, double rail track circuits and double IRJs betweengroups of single rail track circuits shall be used wherever practicable to limitmutual interference. In a.c. electrified areas the traction rail shall be yellowbonded with redundant parallel bonding, as explained in RT/E/S/11752. Regularinspection then ensures that repairs are carried out before all the alternativepaths are exhausted.

Common Rail TC A TC B

RCB

Earth

RSARSB

RCA

RRA RFB RRB

VFA VFB

RFA

Figure 25

Notes for Figure 25 and Figure 26:

TC “A” TC “B”

OPEN CIRCUIT FEED VOLTAGE VFA VFB

FEED RESISTANCE RFA RFB

RELAY RESISTANCE RRA RRB

INSULATED RAIL EARTH RESISTANCE RSA RSB

COMMON RAIL EARTH RESISTANCE RCA RCB



Page 41 of 84

Common RailFurther Track Circuits

RFA

VFA

EarthRRA

RCARCB

RRB RFB

VFB

RSBRSA

Figure 26

Consider also a further example where two track circuits sharing a commonrail through a crossover road suffer wrong side failure due to a break in thatcommon rail bonding. Figure 27 shows the equivalent circuit in track circuittype format whilst Figure 28 converts this to a standard electrical format foreasier presentation of cause and effect.

With the broken bonding, both feed units and relays are in series with the feedunits opposing one another; both relays are therefore de-energised. With thetrain on part of either track circuit, one feed unit is short circuited and theother feeds both relays in series causing a wrong side failure.

Had the polarity of one feedset been reverse, the initial right side failure wouldnot have occurred although the wrong side failure on occupation may still havedone so.

A TR

B TR

d

c a

e

b

A TFU

B TFU

fSee EnlargedDetail Below

x

y

Enlarged DetailBreak

(Broken Bond)

Figure 27



A TR B TR

BrokenBond

d

c

fe

y

x

a

b

A TFU B TFU

A TR B TR

d

c

fe

y

x

a

b

A TFU B TFU

EquivalentCircuit

BrokenBond

Figure 28

This example demonstrates that if a number of track circuits are permitted toshare the use of a common rail, it must be ensured that the hazard arising froma common rail bonding disconnection is prevented. This is achieved bystrengthening the fishplate type bonding at fabricated crossings, usually by theuse of duplicated wire bonds in a ring configuration.

A particular risk due to residual voltage exists with possible IRJ failure where ahigh voltage track circuit abuts a low voltage track circuit when the low voltagetrack circuit is through S&C. To minimise the risk, all IRJs in such areas shall besubjected to a minimum of an annual inspection. Any cases where high and lowvoltage track circuits are designed to share a common rail shall be reported tothe Infrastructure Controller so that the safety of the system can be reviewed.

6.2.1.6 D.C. Point Heaters

The use of d.c. point heaters is not allowed where d.c. track circuits are in use.

6.2.2 Residual Voltage Interference Levels

The differing mechanisms by which extraneous d.c. voltage (voltage notoriginating from the correct feedset) is impressed upon d.c. track relays all raisethe same question: “What level of extraneous voltage is acceptable whilstpermitting normal operation ?”



Page 43 of 84

Residual voltage can arise in a number of different ways or as a combination ofthose ways. The factors governing the value obtained at any instant in time arethemselves very variable (e.g. weather, train positions and traction powerloading). It is therefore necessary to provide a factor of safety to cater forthese unknowns.

A wrong side failure will not occur unless the level of extraneous voltage attainsthat necessary to influence the operation of the track relay (i.e. the drop-awayvalue). The general upper working limit for residual relay voltage is thereforeset at 30% of the drop-away value; below this level, the inability to attain thedrop-away value is assumed and the situation is regarded as safe; above thislevel, it is assumed unsafe unless enhanced supervision or monitoring candemonstrate that the interference is incapable of attaining the drop-away value.

Relaxations to this general rule are given in section 10.1.

6.2.3 Achieving D.C. Immunity

6.2.3.1 Marginal Improvement

Where the level of interference is marginal, it is possible to improve theimmunity to d.c. interference and avoid major expenditure on other forms oftrack circuit:

a) Change the relay. Substituting a relay with higher operating voltages willimprove the safety margin relative to the maximum interference level.However, without change to the feed arrangement, the operational length ofsuch a track circuit is reduced.

b) Add Relay End Resistance. This again increases the rail voltage at which therelay operates relative to the interference level. The same penalty ofoperational length reduction applies unless changes can be made to the feedarrangement.

6.2.3.2 Major Improvement - Convert to Double Rail Configuration

Wherever practicable, which generally applies to plain line in non-electrifiedareas, d.c. track circuits shall be converted from single rail to double rail mode.This prevents interference being imported from adjacent track circuits by wayof the common rail.

However, the source of the interference shall first be ascertained, as, undercertain circumstances, this could prevent a single source of interference frombeing dispersed.



6.2.3.3 Major Improvement - Feed End Relays

All interfering modes introduce the risk of the relay remaining energised whilstoccupied by a train towards the feed end. It follows that provision of a secondrelay at the feed end, separately connected to the rails, as shown in Figure 29,will improve tolerance to such interference, although the additional loadimposed will require a compensating reduction in operational length.

In adjusting track circuits with two relays, it is entirely possible that each relaymay achieve a different drop shunt value. This occurs due to marginaldifferences in relay manufacturing tolerances and the differences in relay endlead resistances. Each relay shall be drop shunt tested separately byobservation of the relay rather than signalbox indication, etc.

Feed end relays do not, however, permit d.c. track circuits to be used in d.c.electrified areas.

TRTR(F)

Figure 29



Page 45 of 84

6.3 IMMUNITY FROM A.C. INTERFERENCE

6.3.1 Sources of A.C. Interference

6.3.1.1 A.C. Traction

In a.c. traction territory, d.c. track circuits are used in single rail mode, sharing acommon rail with the traction return current. A 50Hz extraneous voltage canappear across either the feed or relay end equipment due to longitudinalvoltage drop along the rail similar to d.c. interference as described in section6.2.1.1. The amount of such interference is proportional to track circuit lengthand to the value of traction current. Although the return currents are muchlower than in the d.c. case, this is offset by the higher rail impedance at 50Hz.

6.3.1.2 A.C. Point Heaters

Electric point heaters are supplied by a.c. mains power and, unless specialprotective measures are included in the heater design, certain failure modes canresult in an a.c. interference voltage appearing across the rails. An a.c. immuneversion of track circuit is therefore required.

A new generation of point heater transformers, with double insulationstandards and two separate secondary windings feeding heaters on each rail, areavailable. Such an arrangement will obviate the need for special a.c. immunetrack relays.

6.3.2 Achieving A.C. Immunity

6.3.2.1 Feed Units

A highly inductive choke is placed in series with the output so as to present ahigh impedance to any 50Hz voltage presented across its output terminals fromthe rails. In the case of the a.c. immune non-adjustable feedset, the feedresistance may be embodied within the choke.

It is also necessary to ensure that the feedset does not rectify a.c. voltagepresented on its output terminals, thereby enhancing its d.c. characteristics.



6.3.2.2 Relays

Whilst all d.c. relay mechanisms are to some extent a.c. immune and could bemade more so by use of a series choke, British practice for track relays is toachieve a.c. immunity via the inherent design characteristics of the relay. Anexample of a normal d.c. relay is shown in Figure 30.

NORMAL DC MECHANISM

DC FLUX

Figure 30

AC IMMUNISED DC MECHANISM

DC FLUX

AC FLUX

MAGNETICSHUNT

COPPER SLUGS

Figure 31



Page 47 of 84

The normal d.c. relay mechanism is modified by the addition of copper slugsadjacent to the core face together with a magnetic shunt as shown in Figure 31.The application of d.c. permits operation in the normal way although greaterpower is required due to a proportion of the flux being diverted via themagnetic shunt. The application of an a.c. voltage results in circulating currentsbeing induced in the copper slugs, which oppose the build-up of flux in the airgap; the a.c. flux preferring to circulate via the magnetic shunt.

6.4 ENVIRONMENTAL IMPACT

D.C. track circuits impart no impact on the environment.



7 SAFETY REQUIREMENTS

7.1 SYSTEM SAFETY

The following features are fully described elsewhere in this specification:

• Those types of d.c. track circuit specified for new work generally providethe safety integrity required in RT/E/S/11752, including operation bylightweight vehicles. Where other types of d.c. track circuits are in use, orin areas of heavy rail contamination, mitigation measures may be necessary.

• To guard against bond failure causing a vehicle to go undetected, seriesbonding shall be used wherever practicable. Where impracticable over alength likely to lose a vehicle, yellow bonding must be applied as a mitigationmeasure, as explained in RT/E/S/11752.

• Some delay must be incorporated into d.c. track circuit clearance times, soas to prevent a fast moving train being lost between track circuits.

• To guard against IRJ failure causing false energisation of the track relay,electrical staggering rules must be followed.

• Where necessary, mitigation measures must be taken to preventinterference between adjacent track circuits.

• The minimum operating voltage at the relay must be sufficiently greaterthan any d.c. interference voltage so as to prevent a false energisation of thetrack relay. Track circuit length must be restricted to achieve this. Undercertain circumstances, a feed end relay, or other mitigation, may benecessary.

• Where susceptible to a.c. interference, a.c. immunity must be achieved.

7.1.1 Exposed Terminals

Exposed terminals must be prevented from making electrical contact withother terminals where there is a risk of a component becoming loose or toolsbeing dropped. The preferred method is by shrouding.

7.2 OCCUPATIONAL SAFETY

Special precautions shall be taken to protect personnel from traction voltagesunder fault conditions, including fusing, insulation, labelling and earthing. Theseshall generally be based on BS 7671.



Page 49 of 84

7.2.1 Protective Fusing in Electrified Areas

In electrified areas, a 6A fuse, fully enclosed to BS 88, is to be provided in theapparatus housing in one leg of the track cables (both feed and relay end), asprotection against traction faults, as follows:• Single rail track circuits shall be fused in the insulated rail leg.• Double rail d.c. track circuits are not found in electrified areas.

The removable carrier in the other leg shall be fitted with a shrouded link.

7.2.2 Insulation of Terminals in Electrified Areas

In electrified areas, track circuit tail cable terminations shall be fully shroudedor situated in dedicated enclosures, as described in Code of PracticeRT/E/C/11600. The terminals of all track circuit equipment shall be shroudedor enclosed, except when using the safety procedures for work on electricalequipment.

The shrouding can take the form of a transparent Perspex sheet, which isremovable for maintenance purposes.

7.2.3 Safety Labelling in Electrified Areas

Due to the high voltage present under traction fault conditions, it is necessaryto install warning signs on the outside of all lineside apparatus housingscontaining such equipment.

The "Caution, risk of electric shock" warning signs depict a yellow triangle withlightning flash, as described in RT/E/S/11752, Part J.

7.2.4 Safety Earthing

The standard rules for earthing apparatus housings and class 1 equipment shallbe followed, with all earth bonding shown on the wiring diagrams.



8 DESIGN REQUIREMENTS

8.1 SPECIAL DESIGN REQUIREMENTS

Prior to design, where applicable, a track assessment shall be undertaken, asdetailed in section 2.2.5, to verify the condition of concrete sleepers.

There are no other special design requirements other than those given in thepreceding rules.

8.2 GENERIC DESIGN REQUIREMENTS

The generic design requirements in RT/E/S/11752 include:

• interfaces with authorised rail vehicles (immunity, train shunt capacity,fitment of track circuit assisters, positioning of IRJs, minimum track circuitlengths and interlocking measures to mitigate against any deficiencies), and

• interfaces with the permanent way (IRJs, standard rail bonding with pre-drilling requirements and S&C bonding configuration),

• interfaces with the electric traction infrastructure (immunity and tractionreturn bonding),

• the requirement for secure power supplies or standby batteries (or primarycells for certain non-preferred designs).

• interfaces with the interlocking system (operating times and measures tomitigate against false release of interlocking when there is a significant risk),

For example, steps shall be taken to provide protection when there is asignificant risk due to residual voltage because of high speed facing movementsover S&C where route locking could become ineffective.

8.3 GENERIC DESIGN DELIVERABLES

The design deliverables associated with track circuits that are specified in theSignalling Design Handbook (Code of Practice RT/E/C/11701) include:• signalling/scheme plan,• control tables,• track circuit schedule,• location area plan,• bonding plan (or track plan),• interlocking layout and wiring, and• location layout and wiring.



Page 51 of 84

Track feed polarities shall be shown on bonding/track plans.

Plan symbols shall conform to RT/E/C/11004.

8.4 RECORDING OF DEFICIENCIES

In addition to the above, the designer shall record the following deficiencies onthe signalling plan or bonding plan, as advised by testers, installers ormaintainers:

• any critical or sub-standard clearances at S&C, dimensioned to fouling point.

• where the maximum extraneous value of residual voltage is 30% of relaypick-up voltage, rather than 30% of minimum drop away, as permitted insection 10.1 (Residual Interference Voltage Tests), and

• any lack of correct electrical staggering (see section 3.3).



9 SPECIAL INSTALLATION AND SETTING UP PROCEDURES

9.1 INTRODUCTION

This part shall be read in conjunction with Part J of RT/E/S/11752. Additionalsetting up information is given in Railtrack Line Code of Practice RT/E/C11210,Appendix 2P20. See Appendix 2P25 for high sensitivity adjustment of lowvoltage d.c. track circuits.

These procedures cover setting up the following varieties of d.c. track circuit,as described in section 4:

9.1.1 Standard A.C. Immune Track Circuit With Non-AdjustableFeedset

Fitted with either BR 966 F2 9Ω, BR 939 20Ω or BR 966 F9 60Ω relay,including options to fit either a feed end relay or a relay end adjustmentresistor.

9.1.2 Standard A.C. Immune Track Circuit With Charger / Cells

Charger, cells, choke and adjustable feed resistor working to BR939 20Ω relay,including option to fit either a feed end relay or relay end adjustment resistor.

9.1.3 Diode Track Circuit

Fitted with BR 966 F2 9Ω relay.

9.1.4 Non-Preferred Existing Designs

Fitted with BR 938 4Ω or BS 1659 2.25/9Ω relays.

9.2 FEED END RELAY TR(F)

D.C. track circuits have an option to fit a second relay at the feed end in orderto permit operation with excessive residual interference voltages, although thisreduces the maximum permitted length.

The requirements are given in section 3.5.1.



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No attempt need be made to match the relays, since variations betweenmanufactured relays and differences in tail cable resistance will often causediffering shunt values. Each relay shall have its own “Track Circuit RecordCard” and be drop shunt tested independently. It is necessary to observe theactual relay since the signal box indication may be instigated by the other relaydropping first.

9.3 STANDARD A.C. IMMUNE NON-ADJUSTABLE FEEDSET(MEDIUM VOLTAGE)

9.3.1 Basic Configuration

The basic configuration is a single track relay without any additional relay endresistance.

The feed unit to BR 867 has two flying lead selectors which shall be set up oncommissioning to reflect the application; no adjustment is required in service.

a) Relay Type Selector shall be selected according to relay type:

Terminal 9R for a BR 966 F2 9Ω relay.

Terminal 20R for a BR 939 20Ω relay.

b) Feed Lead Resistance Selector shall be selected according to the feed cableresistance:

Terminal S for short leads (up to 60 metres of 2 core 2.5mm² orequivalent).A short circuit at the rails should give a feedset outputvoltage of 1.2V or less.

Terminal L for longer leads.A short circuit at the rails gives a feedset output voltagegreater than 1.2V.

The drop shunt will generally be in excess of 0.6Ω.

Note: The minimum acceptable drop shunt for this arrangement is 0.5Ω.

9.3.2 Double Relay (without Adjustment Resistor)

The feed unit adjustment is the same as the basic configuration. The drop shuntcan be expected to be slightly higher; there is no need for both the relays todrop at the same shunt value.



Note: the minimum acceptable drop shunt for this arrangement is 0.5Ω foreach relay.

9.3.3 Single Relay (with Adjustment Resistor)

The feed unit is always set up for the 20Ω relay (terminal 20R) regardless ofwhich relay type is actually used. The relay end resistor is adjusted such thatthe relay picks up at a rail voltage in the range 2.8V - 3.0V. The shunt box witha parallel connected voltmeter can be used to adjust the rail voltage for set-uppurposes.

a) Set the relay adjustment resistance to a high value and the shunt box to alow value such that the relay is down.

b) Increase the shunt box value until the rail voltage stands at 3.0V.

c) Lower the relay adjustment resistance until the relay just picks.

d) If the rail voltage has dropped below 2.8V, increase the shunt box to bringthe rail voltage back to 3.0V. Increase the relay adjustment resistance to ahigher value to drop the relay, then lower it again until the relay just picksup. Check that the rail voltage has not dropped below 2.8V.

e) Having achieved a satisfactory set-up, undertake a normal drop shunt test.


9.3.4 60ΩΩ Relay

The feed unit is always set up for the 20Ω relay (terminal 20R) despite a 60Ωrelay being fitted. It is also set for long feed leads (terminal L) regardless oftheir actual length.


9.4 STANDARD A.C. IMMUNE WITH BATTERY STANDBY (MEDIUMVOLTAGE)

9.4.1 Basic Configuration

This design uses a 12V battery charger and cells with a choke similar to a BR867 feed unit in series with a BR 3000 Appendix 1, 0 - 8Ω feed resistor. It isdesigned to operate with a BR 939 20Ω relay and has the ability to additionallysupport either a feed end relay or a BR 3000 Appendix 2 adjustable resistor inseries with the relay to obviate residual voltage problems.



Page 55 of 84

The feed resistor shall be adjusted such that when an ammeter is connectedacross the rails at the feed end, the registered current is in the range 1.1A -1.25A.

The drop shunt will generally be in excess of 0.6Ω.


9.4.2 Double Relay (Without Adjustment Resistor)

The feed arrangement and adjustment is the same as the basic configuration.The drop shunt can be expected to be slightly higher; there is no need for boththe relays to drop at the same shunt value.

Note: The minimum acceptable drop shunt for this arrangement is 0.5Ω foreach relay.


The feed arrangement and adjustment is the same as the basic arrangement.The relay end resistor is adjusted such that the relay picks up at a rail voltage inthe range 2.8 - 3.0V. The shunt box with a parallel connected voltmeter can beused to adjust the rail voltage for set-up purposes.

a) Set the relay adjustment resistor to a high value and the shunt box to a lowvalue such that the relay is down.


c) Lower the value of the relay adjustment resistor until the relay just picksup.

d) If the rail voltage has dropped below 2.8V, increase the shunt box to bringthe rail voltage back to 3.0V. Increase the relay adjustment resistor to ahigher value to drop the relay, then lower it again until the relay just picksup. Check that the rail voltage has not dropped below 2.8V.





9.5 THE DIODE TRACK CIRCUIT (MEDIUM VOLTAGE)

Due to the fact that the diode track circuit is generally restricted to levelcrossing controls, the diode end of the track circuit contains the wiring for thetreadles. It should be noted that during the testing of the track circuit both thetreadles shall be functioned individually with the track circuit clear.

The adjustable resistance at the feed / relay end of the track circuit is set bystrapping the various terminals on the front of the unit. These straps are madeusing stranded 1.15mm² wire with a ring terminal at each end and the numberof straps used and the settings shall be recorded on the track record card. Thevalue of the adjustable resistor is selected to give a minimum drop shunt of1.5Ω.

Typical settings are as shown in Figure 32.

1 2 3

4 5 6

1 2 3

4 5 6

1 2 3

4 5 6

1 2 3

4 5 6

1 2 3

4 5 6

1 2 3

4 5 6

1 2 3

4 5 6

I/P O/P I/P O/P I/P O/P I/P O/P

O/P

I/P O/P I/P O/P I/P O/P

O/PO/PO/P

33 ohms 22 ohms 13.2 ohms 11 ohms

5.5 ohms8.8 ohms 7.3 ohms

Figure 32

The internal wiring of the adjustable resistor unit is as shown in Figure 33.R1, R2, R3 and R4 are 22Ω , 100 watt resistors.



Page 57 of 84

1

2

3

4

5

6

R1

R2

R3

R4

Figure 33


9.6 NON-PREFERRED EXISTING DESIGNS USING BR 938 4ΩΩ ANDBS 1659 2.25ΩΩ AND 9ΩΩ RELAYS

9.6.1 General

These track circuits have been installed in a variety of forms using primary cells,trickle charged secondary cells or transformer / rectifiers with a seriesadjustable resistor at the feed end, and either the BR 938 4Ω plug-in or the BS1659 2.25Ω /9Ω shelf type relay at the other.

In their basic configuration with a single relay connected directly across therails, they are classed as low voltage, and “barred” relative to lightweight Class14X - 16X rail vehicles not fitted with TCAs.

The detection performance can be improved by additional resistance in serieswith the relay accompanied by a “high sensitivity” method of adjustment,although the extent of the improvement is limited by the power available fromthe feed.

It is also possible to fit feed end relays, with or without an adjustable resistor,to some designs.

The four feed arrangements can be placed into two groups for mix / matchpurposes with the relays:



9.6.2 Group A Feed Arrangement

This group comprises feeds with a source voltage of less than 2 volts:

• Two CS2 primary cells in parallel.

• Battery charger with one NiCad cell.

Track circuits with this feed arrangement cannot be sufficiently improved by aninsertion of adjustable resistance in series with the relay. They are not suitablefor the detection of Class 14X - 16X lightweight vehicles, unless fitted withTCAs.

9.6.3 Group B Feed Arrangement

This group comprises feeds with a source voltage in the range 2 - 3 volts:

• Two CS2 primary cells in series.

• Battery charger with one lead acid cell.

Track circuits fitted with this feed and either a 4Ω or 9Ω relay have sufficientpower to enable high sensitivity adjustment to achieve acceptable operationwith Class 14X - 16X lightweight vehicles not fitted with TCAs (but this is onlypermitted on uni-directional lines or where sequential track circuit proving is inuse).

9.6.4 Adjustment of the Basic Configuration

The basic configuration is defined as having a single relay connected directlyacross the rails without an adjustable resistor in series with it.

Connect an ammeter across the rails at the feed end and adjust the feedresistor to give a current as close as possible to the value in Figure 34, butwithout exceeding that figure:



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Feed Type Relay Type Short CircuitFeed Current

Group AGroup AGroup A

BS 1659 2.25ΩBS 1659 9ΩBR 938 4Ω

130mA420mA

Not Viable

Group BGroup BGroup B

BS 1659 2.25ΩBS 1659 9ΩBR 938 4Ω

130mA420mA600mA

Figure 34


9.6.5 Double Relay (without Adjustment Resistor)

It is stressed that whereas this configuration overcomes the problems ofresidual interference voltages, it does not improve detection of poor vehiclesand / or poor rail surfaces.

Connect an ammeter across the rails at the feed end and adjust the feedresistor to give a current as close as possible to the value in Figure 35, butwithout exceeding that figure.


Group AGroup AGroup A

BS 1659 2.25ΩBS 1659 9ΩBR 938 4Ω

Not Viable490mA

Not Viable


BS 1659 2.25ΩBS 1659 9ΩBR 938 4Ω

Not Viable450mA700mA

Figure 35

The drop shunt can be expected to be slightly higher than the basicconfiguration.





Connect an ammeter across the rails at the feed end and adjust the feedresistor to give a current as close as possible to the value in Figure 36 butwithout exceeding that figure:


Group A BS 1659 2.25Ω Not Viable


BS 1659 2.25ΩBS 1659 9ΩBR 938 4Ω


Figure 36

The relay end resistor is adjusted such that the relay picks up at a rail voltage inthe range 0.8V - 1.0V. The shunt box with a parallel connected voltmeter canbe used to adjust the rail voltage for set-up purposes.

a) Set the value of the relay adjustment resistor to a high value and the shuntbox to a low value such that the relay is down.


c) Lower the value of the relay adjustment resistor until the relay just picksup.

d) If the rail voltage has dropped below 0.8V, increase the shunt box value tobring the rail voltage back to 1.0V. Increase the relay adjustment resistor toa higher value to drop the relay, then lower it again until the relay just picksup. Check that the rail voltage has not dropped below 0.8V.


Note: The minimum acceptable drop shunt for this arrangement is 1.2Ω .

9.6.7 Double Relay (with Adjustment Resistor)

Connect an ammeter across the rails at the feed end and adjust the feedresistor to give a current as close as possible to the value in Figure 37, butwithout exceeding that figure.



Page 61 of 84


Group A BS 1659 2.25Ω Not Viable


BS 1659 2.25ΩBS 1659 9ΩBR 938 4Ω


Figure 37

a) Reduce the value of the adjustment resistor of the track relay until it picksup. Connect the shunt box / voltmeter across its coil and determine thevoltage at which it just picks up (Vpu). Remove the shunt box / voltmeterand set the value of the adjustment resistor according to the followingformula:

x R Relay Resistance0.8 - Vpu

Adjustment Resistance = Vpu

b) Adjust the track feed relay in accordance with the method given for theSingle Relay (with Adjustment Resistor) option.

c) Adjust the track relay in accordance with the method given for the SingleRelay (with Adjustment Resistor) option.

d) Having achieved a satisfactory set-up, undertake a normal drop shunt testfor each relay separately (i.e. observe the TR itself to drop and do not use aTPR or panel indication); there is no need for both relays to drop at thesame shunt value.


9.6.8 Difficulties with Setting Up

9.6.8.1 Unable to Obtain Sufficient Feed Current

Since feed resistance is only adjustable in steps of 0.5Ω, the selected adjustmentshall be the 0.5Ω step which reduces the feed current below the stipulatedmaximum for the particular configuration. In order to identify this settingcorrectly, it should be possible to first adjust to a feed current above themaximum and then increase resistance in 0.5Ω steps.



If the maximum feed current cannot be exceeded and the power supply and allconnections are satisfactory, the problem is probably due to the feed tail cableresistance being too high. Install duplicate / parallel or larger conductor feedtail cables.

9.6.8.2 Relay will not Energise at Specified Rail Voltage

When setting a relay end adjustment resistor, the relay remains down evenwhen the adjustment resistance value is reduced to zero.

This is probably due to the relay end tail resistance being too high. Check thatall connections are satisfactory. If no improvement can be made, installduplicate / parallel or larger conductor relay end tail cables to reduceresistance.



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10 SPECIAL TESTING PROCEDURES

These Procedures shall be read in conjunction with Part K of RT/E/S/11752 andSignalling Works Testing Handbook.

10.1 RESIDUAL INTERFERENCE VOLTAGE TESTS

This test shall be applied to all d.c. track circuits not fitted with a feed end relay.It shall be undertaken with all adjacent track circuits energised.

Connect a voltmeter across the relay coils and disconnect the associated feedunit from the rails. In the case of a diode type track circuit, both the diode andthe connections between the feed transformer and the relay shall bedisconnected within 5 seconds of each other.

After an elapsed period of 120 ±5 seconds, the voltage across the track relaycoils shall be recorded and related to the values given in the Figure 38.

If the measured voltage exceeds the quoted 30% of minimum drop away, thesource of the extraneous voltage shall be investigated and appropriate remedialaction taken. To enable commissioning to continue, the following relaxationsare permitted:

a) Where the track circuit is used solely for control of ABCL or AOCL levelcrossings where its failure to detect a train would be protected by theDriver’s Crossing Indicator. The circuitry shall additionally ensure thatpremature clearance will result in the white light of the Driver’s CrossingIndicator being extinguished for at least 30 seconds before the road lightscease to flash. If all these conditions are met, commissioning may continueas normal.

b) Where residual relay voltage does not exceed 70% of the drop away value,the track circuit may remain in service provided that any jumpers in thebonding are duplicated and that the bonding is specially inspected / repairedat four-weekly intervals. This dispensation is granted only to provide timeto design and install a permanent solution and is limited to a period of twoyears.

c) Where normal signalled movements always run onto the relay end of thetrack circuit, the maximum extraneous value permitted may be raised to30% of relay pick-up voltage. Where this clause is invoked, the signallingscheme plan shall be endorsed to that effect.



BR/BSSpecification

Resistance(ΩΩ)

Pin Code Drop AwayVolts

30% 70%

30% of PickUp Volts

BS 1659BR 938BR 939BR 966 F2BR 966 F9

94

209

60

-101105110104

0.070 0.1600.075 0.1750.298 0.6950.198 0.4620.571 1.332

0.1030.1110.4380.2910.840

Figure 38

10.2 CATHODIC PROTECTION TESTING

The standard for cathodic protection is BS 7361-1 and the associated risks areidentified in Railway Group Standard GL/RT1253.

The following tests measure the interference effect of a cathodic protectionscheme on an individual track circuit under normal and fault conditions.

It is not necessary in all cases to perform all the tests if the rail to soil potentialis found to be under 20mV, as detailed tests are then unnecessary (see Test 1).In electrified areas, all negotiations and arrangements with outside parties shallbe made via the organisation responsible for electrification infrastructure.

Outside party to provide switching on and off of the cathodic protection at theground bed (usually provided by an automatic timer e.g. 2 minutes on / 2minutes off).

Note: all potentials to earth are taken with respect to a reference cell.(Metering in this respect is usually supplied by the outside party at the time ofthe tests.)

10.2.1 Tests

If the pipeline crossing is within the track circuit (see Figure 39) carry out Tests1, 2 and 4.

If the pipeline crossing is outside the track circuit (see Figure 40) carry outTests 3 and 4.



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U

V

A

F

B

E

C

D

W

X

ST

TR

FEED

PIPELINE

Figure 39

U

V

A

F

B

E

C

D

W

X

S T

TR

FEED

PIPELINE

Figure 40

10.2.1.1 Test 1

Record the rail / soil potential swing at points A, B, C, D, E and F, and betweenC and D with cathodic protection on and off.

If more than 20mV swing at any point, proceed to Test 2. If less than 20mV,the interference is negligible.

10.2.1.2 Test 2

Simulation of IRJ and Feed failure:

a) Disconnect track feed.

b) Short circuit IRJs at U and W.

c) Measure potential across track relay with cathodic protection on and off.



d) Remove short circuits at IRJs U and W.

e) Short circuit IRJs at V and X.

f) Repeat c) above.

g) Remove short circuits at IRJs V and X.

h) If more than 30% of the TR drop away voltage is seen in c) or f), interferenceexists and remedial action is necessary.

i) Proceed to Test 4.

10.2.1.3 Test 3

a) Disconnect track feed.

b) Short circuit IRJs U and X.

c) Measure voltage across TR with cathodic protection on and off.

d) Remove short circuits at IRJs U and X.

e) Short circuit IRJs V and W.

f) Repeat c) above.

g) Remove short circuits at IRJs V and W.

h) If in c) or f) above the voltage measured is greater than 30% of the relaydrop away voltage, remedial action is necessary.

i) Proceed to Test 4.

10.2.1.4 Test 4

a) Simulation of track relay earth fault:

b) Disconnect track feed and disconnect TR at point S and connect temporaryearth T to relay at point S.

c) Short circuit IRJs U and W.

d) Measure voltage across relay coil with cathodic protection on and off.

e) If the voltage is greater than 30% of TR drop away voltage, remedial action isnecessary.

10.2.2 Remedial Actions

Remedial action shall be taken where required. Any of the following measures,singly or in combination, may be employed.

• Arrange for the outside party to use a lower level of cathodic protection.

• Reduce the resistance of the track relay coil.



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• Shorten or re-configure the track circuit.

• Transpose the feed and relay ends.

• Convert to a “high voltage” design of track circuit (using 20Ω track relay).

• Convert to a non d.c. design of track circuit.

On completion of remedial action a full test shall be carried out.



11 SPECIAL MAINTENANCE PROCEDURES

11.1 INTRODUCTION

This part details special maintenance procedures for d.c. track circuits.

General maintenance requirements are contained in Part M of RT/E/S/11752.General maintenance procedures are given in Signalling MaintenanceSpecification TC01.

11.2 IRJ TESTING

11.2.1 Introduction

In addition to the procedures for determining the condition of IRJs detailed inPart K of RT/E/S/11752, it is possible to carry out ”in situ” testing of IRJs undercertain circumstances where d.c. track circuits are involved. The followingprocedure is extracted from Signalling Maintenance Specification TC01:

11.2.2 Testing

The following tests are intended to indicate partial breakdown of insulation sothat appropriate actions to prevent total failure can be taken. The tests arecarried out with the track circuits in service and are valid if the followingconditions apply:

a) The track circuits on each side of the IRJ are of the same type.

b) The electrical stagger of the track circuits on each side of the IRJ is correct

c) Wooden insulated rail joints are not involved.

Before commencing the tests, check that both the track feed units are workingcorrectly and that there are no disconnections or short circuits on either ofthe track circuits. A technician's digital multi-meter or similar instrument shallbe used. The sequence is as follows:

1. The metal components of the IRJ shall be cleaned to provide good electricalconnections for all measurements.

2. Connect a 220Ω shunt resistor (Catalogue No. 86/43999) across the meterand measure its resistance. If this is outside the range 200Ω - 240Ω, reapplythe shunt resistor before proceeding with the test.



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3. Set the meter to the correct voltage range (determined by the operatingvoltages of the track circuits).

4. If the IRJ to be tested is on a double rail track circuit, the opposite associateIRJ must be short circuited to form the test circuit. It should be noted thatthis may cause both track circuits to show occupied.

5. Using the meter fitted with the 220Ω shunt resistor, measure the rail to railvoltage across the IRJ. Note this voltage (if it is zero, the joint has failed orthe track circuits are not correctly staggered).

6. Measure the voltage between one plate of the IRJ and the rail on both sidesthe IRJ. Note these voltages.

7. Repeat the measurements for the plate on the other side of the IRJ. Notethese voltages.

8. Remove the shorting strap (if fitted for item 4).

The various test measurements to be taken are indicated in Figure Fl.

Rail Rail

Test 6 Test 6

Insulation

Test 7 Test 5 Test 7

Figure 41

The results of the tests are interpreted as follows:

• If the rail to plate voltage readings are less than one tenth of the rail to railreading, the joint is satisfactory.

• If the rail to plate voltage readings are between one tenth and one half ofthe rail to rail reading the joint is likely to fail and requires attention. Thisshall be reported to the infrastructure controller.

• If any rail to plate voltage reading is above one half of the rail to rail reading,a part of the joint has failed and requires attention. This shall be reported tothe infrastructure controller who shall inform the organisation responsiblefor the permanent way immediately.



Note: It should be remembered that some designs of IRJ have the bolts incontact with the rails.

11.2.3 Prefabricated IRJs

“Edilon” and similar prefabricated IRJs shall be tested prior to installation in thetrack. Details are contained in Part K of RT/E/S/11752.

11.3 TRACK CIRCUIT MAINTENANCE RECORD CARDS

Examples of the Track Circuit Maintenance Record Cards for d.c. and diodetrack circuits are shown in Figure 42, Figure 43, Figure 44 and Figure 45 . Theappropriate card shall be completed for all maintenance visits and following anytrack circuit repairs.



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Figure 42



Figure 43 (Reverse of Figure 42)



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Figure 44



Figure 45 (Reverse of Figure 44)



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12 SPECIAL FAULT FINDING PROCEDURES

12.1 INTRODUCTION

This part deals with the diagnosis and repair of failures on basic d.c. trackcircuits. It shall be read in conjunction with Part P of RT/E/S/11752 thatexplains how to define types of failure present.

Staff without experience of d.c. track circuits shall familiarise themselves withthe sequential testing procedure before committing to an actual fault.

12.2 SEQUENTIAL TESTING

This fault finding procedure assumes that the track relay is not energised. It isbased on sequentially testing the equipment and wiring to isolate the location ofthe fault in a manner which minimises movement from one test location toanother. There is no standard order in which to isolate the fault, each casemust be dealt with on its own merits. In each case, if one test cannot reveal thefailure then another test must be undertaken as directed.

It will be instructive to consult the Track Circuit Maintenance Record Card tosee which readings have dramatically changed, thus giving an indication as to thesource of the failure.

It is recommended that spares be carried for immediate on-site replacement.

12.2.1 Relay End Relay Voltage: Test T1

This test is to check if the track relay is faulty.

Measure the voltage across the relay coil.

Result (a): Voltage is within specified limits.

Action: Replace track relay.

Result (b): Voltage is low.

Action: Check relay end resistor (if fitted).If fault remains, proceed to Feed end relay status (test T3).

Result (c): No voltage found.

Action: Proceed to relay end rail voltage (test T2).



12.2.2 Rail Voltage at the Links of the Relay End Lineside ApparatusHousing: Test T2

This test is to check the integrity of the lineside apparatus housing wiring.


Action: Check lineside apparatus housing wiring.If fault remains, return to Relay end voltage (test T1).


Action: Proceed to Track short or bonding disconnection (test T5).


Action: If feed end relay is fitted, proceed to Feed end relay status(test T3).

If a feed end relay is not used, proceed to Feed end voltage at lineside apparatushousing (test T6).

12.2.3 Check the Feed End Relay Status (if fitted): Test T3

Observe the position of the relay contacts.

Result (a): Relay is up.

Action: Possible bonding fault.Proceed to Track short or bonding disconnection (test T5).

Result (b): Relay is down.

Action: Possible feed fault.Proceed to Feed end relay voltage (test T4).

12.2.4 Feed End Relay Voltage: Test T4

This test is to check if the feed end relay is faulty.Measure the voltage across the relay coil.



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Action: Check lineside apparatus housing wiring.If fault remains, proceed to Track short or bondingdisconnection (test T5).


Action: If fault remains, proceed to Track short or bondingdisconnection (test T5).


Action: Proceed to Feed end voltage at lineside apparatus housing(test T6).

12.2.5 Track Short or Bonding Disconnection: Test T5 (seeRT/E/S/11752, Part P)

Test the track circuit for a disconnection of the bonding or short circuit.

Result (a): Track fault found.

Action: Repair or report as required.

If difficulty is encountered in finding the fault, the Track Circuit Fault Detectormay be used (see RT/E/S/11752, Part N).

12.2.6 Feed End Voltage at Lineside Apparatus Housing: Test T6

This test is to verify the integrity of the tail cables.Measure the voltage across the feed end output links.


Action: Check feed end tail cables and feed end relay tail cables (iffitted).

Result (b): No or low voltage.

Action: If battery fed, check cells and / or charge apparatus.If a feedset is used, proceed to Supply to feedset (test T7).



12.2.7 Supply to Feedset: Test T7

This test is to verify the operation of the feedset.Measure the voltage supply to the feedset.


Action: Change feedset.

Result (b): No voltage found.

Action: Check 110V fuses.If fault remains, tests on the 650V a.c. supply will be required.(Not covered by this specification).

12.3 RE-TESTING

When the fault has been found, the track circuit shall be re-tested inaccordance with Signalling Maintenance Specification TC01.



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13 REFERENCES

Railway Group Standards

GL/RT1253 Mitigation of D.C. Stray Current Effects (supersedes GM/RT1018)

Railtrack Line Standards

RT/E/C/11004 Symbols for Plans and Sketches Used in Signalling Applications(supersedes GK/RT0004)

RT/E/C/11210 Signalling InstallationAppendix 2P20 Track Circuits: D.C. (supersedes GS/IH2P20)Appendix 2P25 Track Circuits: D.C. High Sensitivity

(supersedes GS/IH2P25)

RT/E/C/11552 Signalling Maintenance Specifications Contents(to be superseded by RT/E/S/10660)

RT/E/C/11600 Signalling and Operational Telecommunications Design:Technical Guidance (supersedes GK/GN0600)

RT/E/C/11701 Signalling Design: Production Guidance(supersedes GK/RC0701)

RT/E/G/11710 Signalling Design Handbook (supersedes GK/RH0710)

RT/E/G/11720 Signalling Installation Handbook (supersedes GS/IH0001)

RT/E/G/11730 Signalling Works Testing (supersedes GK/RH0730)

RT/E/G/11740 Signalling Maintenance Testing(supersedes GK/RH0740)

RT/E/S/11752 Train Detection (supersedes GK/RC0752, etc.)

EHQ/PR/S/004 Procedure for Cathodic Protection (status uncertain)

RT/E/S/11764 Track Circuit Interrupters

BR Specifications

BR865 Transformer Rectifier Units for General Railway SignallingPurposes

BR867 A.C. Immune Track Feed Circuits



BR933 Miniature Tractive Armature A.C. Immune D.C. Slow Pick-upNeutral Line Plug-In Type for Railway Signalling Purposes

BR938 Miniature Tractive Armature D.C. Neutral Track Relay Plug-InType for Railway Signalling Purposes

BR939 Miniature Tractive Armature A.C. Immune D.C. Neutral TrackRelay Plug-In Type for Railway Signalling Purposes

BR966 Relays, Miniature Tractive Armatures, Plug-In Type for RailwaySignalling Purposes

BR967 Railway Signalling Apparatus: Environmental Conditions

BR1875 Battery Charger Units for General Railway Signalling Purposes

BR3000 Track Circuit Adjustment Resistance

Signalling Maintenance Specifications (see RT/E/C/11552)

TC01 Track Circuit, General Procedure

National / International Standards

BS 88 Cartridge fuses for voltages up to and including 1000 volts a.c.and 1500 volts d.c.

BS 1659 Specification for tractive armature direct current neutral trackand line relays for signalling equipment

BS 7361 Cathodic Protection

BS 7671 Requirements for Electrical Installations (IEE Wiring Regulations)



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14 GLOSSARY

The terms used throughout this Product Specification are defined inRT/E/S/11752.



APPENDIX A LIST OF COMPONENTS

This appendix lists the components required for the various types of d.c. trackcircuit.

Note: The Catalogue Numbers shown within this document are not directlycontrolled by Railtrack and as such, will not be maintained and kept up to date.Although every effort has been made to ensure that these were correct at thetime of publication, it is therefore recommended that your supplier iscontacted and a check is made with regard to the accuracy of these cataloguenumbers prior to use.

A.1 BONDING

Details of bonding components can be found in RT/E/S/11752, Part J. Thefollowing component types are used on d.c. track circuits:

A.1.1 Fishplate Type Bonding

Two No. 8 swg GI bonds secured by sherardized tapered bond pins insertedinto pre-drilled 7.2mm holes at 76mm centres, 57+2mm from the foot of therail and hammered firmly in, to make good electrical contact with the rail.

A.1.2 Feed & Relay Leads

Single or duplicated 2.5mm2 flexible single leads with moulded rubber ends.

A.1.3 Jumper Bonding (except traction rail on electrified lines)

2.5mm2 flexible single core cable using either moulded rubber connectors and

in-line cable joint(s), or a single cable length attached to the rail with “L” plateconnectors.

A.1.4 Jumper Bonding (traction rail)

Heavy current traction jumper cable supplied, installed and maintained by theorganisation responsible for electrification infrastructure.



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A.2 PRIMARY CELL BATTERIES

Description Catalogue No.

Primary Cell CS2 (formerly AD618A) 54/148150

A.3 TRANSFORMER / RECTIFIER UNITS


Feed Unit to BR 865 Appendix 6, Input: 110V a.c., Output: 6V 2A.Maximum width - 110mm (Two relay modules).

86/43570

Feed Unit to BR 865 Appendix 5, Input: 110V a.c., Output: 2V 1A.Maximum width - 110mm (Two relay modules).

86/43951

Feed Unit to BR 867 a.c. Immune, Input: 110v a.c., Output: 10V 1.5A.Maximum width - 285mm (Five relay modules).

86/43853

A.4 BATTERY CHARGERS & SECONDARY CELLS


Battery Charger to BR 1875, Input: 110/240V a.c., Output: 2V 1A. Tocharge 1 x NiFe/NiCad cell.

86/1650

Battery Charger to BR 1875, Input: 110/240V a.c., Output 12V 3A. Tocharge 6 x lead acid or 9 x NiCad cells

86/1906

Single lead acid cell 30Ah 54/41330

Crate of five NiCad cells 16Ah 54/41318

A.5 TRANSFORMERS


Transformer for Diode Track Circuit 110/24V 120 VA. 54/89696

A.6 ADJUSTMENT RESISTORS


Adjustable Resistor to BR 3000 Appendix 1, 0 - 8Ω , 12W. For feed end.Maximum width - 55mm (one relay module).

86/43571

Adjustable Resistor to BR 3000 Appendix 2, 0 - 24Ω , 1.5W. For relay end.Maximum width - 55mm (one relay module).

86/43572

Adjustable Resistor to BR 3000 Appendix 3, 0 - 60Ω , 4W. For relay end.Maximum width - 55mm (one relay module).

86/43575

Adjustable Feed Resistor for Diode Track Circuit 33Ω Adj. 86/43459

A.7 FUSE / DISCONNECTION LINKS


Fuseholder Camaster 32A Front Connected 54/72164



Safety Locking Camaster 32A Fuse Carrier. 54/77742

Fuse Type TIA6 54/106554

Solid Link for Fuseholder 54/77744

A.8 RELAYS


Relay to BR 939, 20Ω , a.c. immune, Pin Code 105. 85/250

Relay to BR 966 F2, 9Ω , a.c. immune, Pin Code 110 85/280

Relay to BR 966 F9, 60Ω , a.c. immune, Pin Code 104 85/230

Relay to BR 938, 4Ω , Pin Code 101 85/200

Relay to BS 1659, 2F/B Shelf Type, 9Ω (Black Coils) Fixed Top 88/30159

Relay to BS 1659, 2F/B Shelf Type, 9Ω (Black Coils) Remax Top LMR Type. 88/30189

Relay to BS 1659, 2F/B Shelf Type, 9Ω (1 Red/Black Coils) Fixed Top 88/30160

Relay to BS 1659, 2F/B Shelf Type, 9Ω (2 Red Coils) Fixed Top 88/30161

Relay to BS 1659, 2F 2F/B Shelf Type, 9Ω Fixed Top. 88/30162

Relay to BS 1659, 2F 2F/B Shelf Type, 9Ω Remax Top LMR Type 88/30287

Relay to BS 1659, 2F 2F/B Shelf Type, 9Ω Remax Top ER Type 88/30291

Relay to BS1659, 2F 2F/B Shelf Type, 9Ω (a.c. Immune) Fixed Top. 88/30169

Relay to BS1659, 2F 2F/B Shelf Type, 9Ω (a.c. Immune) Remax Top LMR Type. 88/3019

A.9 CHOKES


Choke from BR 867 feedset for use with Track circuits —

A.10RECTIFIER TERMINATION UNITS


Rectifier Termination Unit for Diode Track Circuit. 86/43460

Rectifier Termination Unit for Diode Track Circuit with Level CrossingApplications

—

Stake for Mounting Termination Unit 760mm long. 86/10751

Stake for Mounting Termination Unit 1070mm long 86/10751

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