21.1.1 The relay interlocking installations can be of: -

i) Route setting type by entry/exit.

ii) Non-route setting type i.e. Route is set with individual operation of points.

21.1.2 The equipment used in the system shall, as far as practicable, comply with the requirements of IRS, IS, BRS and BS specifications and drawings.

21.1.3 For areas having 25KV AC traction, all equipments and circuitry shall comply with the requirements of Chapter XXII on "Special requirements of signalling in AC electrified areas".

21.1.4 The signalling and interlocking arrangements for the yard shall be in accordance with the approved signalling plans, selection/control tables, detailed wiring diagram including control panel diagram, relay contact analysis and relay rack arrangements.


21.2.1 The display of the layout on the front of the panel referred to as the illuminated diagram shall be well proportioned. Where additional facilities are likely to be provided, domino type panel shall, preferably, be used. The areas covered by each track circuit shall be clearly distinguished by use of different colours.

21.2.2 The illuminated diagram shall be so mounted as to be conveniently visible to the operator. The control panel shall be easily accessible for operation. The inside wiring etc. should be such that it is easily accessible for maintenance staff.

21.2.3 The operating members, namely route switches/buttons, point switches etc., referred to in the following clauses shall normally be provided on the illuminated diagram itself in Geographical order. A separate illuminated diagram for indication and a separate 'console' containing all the operating members may also be provided.

21.2.4 The route setting shall be on the basis of "Entrance Exit" principle for installations of Route Setting type.

21.2.5 At Non route setting type installations, the route may be set with individual operation of points.

21.2.6 In route setting system, each route shall be controlled either by means of two push buttons-one at the entrance and the other at the exit of the route or by means of one switch at the entrance and one push button at the exit of the route. The entrance switch button may be of three position type or two position type as required.

21.2.7 In non route setting type installations, after setting of the route by individual operation of points is completed, signal can be cleared by an individual push button in conjunction with a group button or by an individual switch controlling each signal or a common switch for conflicting signals which are not required at the same time, or one push button at the entrance and other at the exit end.

21.2.8 Individual push button in conjunction with a common push button or two/three position switches shall be provided for individual operation of points.

21.2.9 Where a route has more than one overlap, it shall be possible to select and set the desired overlap beyond the exit signal of the route.

21.2.10 Where the route has alternate approach routes, it shall be possible to select and set the desired route with desired overlap.

21.2.11 The switches/buttons shall have distinctive colours so that they can be readily distinguished, such as running signal red, shunt signal yellow, calling on signal red with white dot & exit button white. The alternate overlap white with black dot, alternate route Grey, point black, slot green, crank handle blue and point group button black with red dot etc.

21.2.12 The control panel shall be provided with suitable covers with locking and sealing facility which shall be easily removable to facilitate access to the internal wiring etc.

21.2.13 The control panel shall be provided with:-

a) Arrangement for individual operation of points.

b) Arrangement for emergency operation of points where provided, during point zone track circuit failures. Emergency group point button for such operation must be kept normally sealed. Each such individual operation shall be recorded on a suitable counter.

c) Necessary slotting facilities for adjoining cabins, ground-frames, level crossings and crank handles etc.

d) Arrangement so that slot shall be controlled by operation of two buttons or a switch similar to route setting principle for individual line. For cancellation of slot a group slot cancellation button to be operated along with entrance/exit button shall be provided. Each such cancellation shall withdraw the slot but the route controlled by the slot shall be kept held for a predetermined time delay or till route locking if any, is effective. Each cancellation shall be recorded in a counter specially provided for this purpose.

e) Arrangement to adjust the supply voltage for panel indication circuit to control the intensity of illumination by selecting different supply voltages with the help of button/switches provided on the panel, if necessary.

f) When SM's key is taken out, it shall not be possible to change the last operated position of any signalling apparatus from control panel. However, facility shall be provided to put back the signal to 'ON' position without altering the route. It shall preferably be ensured that no command gets executed automatically on reinsertion of SM's key.

21.2.14 An indication panel giving position of the yard and important indications required for maintenance staff shall be provided inside the relay room in major yards.


The control panel shall be provided with the following indications :-


a) The position of points shall be indicated either by white/yellow or green lights near each individual point switch/button or by white strip light on the point zone. During operation of the points, light/strip light for the intended position will flash till points are correctly set and locked.

b) The point locked indication in route shall be given by illumination of a small white light near the point or points switch/button which shall be extinguished when point is free.


a) Route indication lamps shall be provided to indicate setting and locking of the route. When any route is not set, route indicator lamps shall be extinguished.

b) The complete route over which the movement is to take place shall be lit with a row of white lights when the route is correctly set and locked.

c) As the train moves over the route, the portion of the route occupied shall change to red and after the train has cleared the particular track, it should change back to white lights until the sectional route/entire route is released, when the white light is extinguished.


a) Indication that a stop signal is at 'ON' shall be given by a red light and a permissive signal is at 'ON' shall be given by a yellow light on the corresponding signal symbols on the panel.

b) Indication that stop/permissive signal is 'OFF' shall be given normally by a green, yellow or double yellow light as signal is seen in the field, on the corresponding signal symbol on the panel. However, in case of a domino panel where indication of all aspects is not provided, any 'OFF' aspect can be shown by green along with the following flashing indications for conditions as enumerated below:-

i) Failure of green; green flashes red* blank;

ii) Failure of yellow; green flashes, red lit;

iii) Failure of double yellow, both green and red* flash; &

iv) Failure of red*, green not lit (blank), red* flashing.

*To be read as yellow for a permissive signal.

c) Signal indication for the 'ON' aspect of a shunt signal on the same post as the running signal is not required. In the case of shunt signal on independent post, the 'ON' indication shall be given by a white light strip or two miniature white lights in a horizontal position on the corresponding shunt signal symbol on the panel.

d) Signal indication for 'OFF' aspect of a shunt signal shall be given by a slanting white light strip or two miniature slanting white lights. Such indication of a shunt signal located on the same post as a running signal shall be given below the running signal indication.

e) A white light for 'A'/'AG' marker indication should be lit up on the panel below the symbol of the signal when set for automatic working.

f) Indication that "Calling on" signal is 'OFF' shall be given by a white light below the running signal indication of corresponding signal symbol.

g) Repeat indication shall be provided by a white strip light which should be lit when repeater of the signal has displayed 'OFF' aspect. This indication should be provided by a white strip over the running signal symbol on the panel.


a) Indication that the track circuit is occupied shall be given by a row of red lights (not less than two) on the each track circuit portion.

b) When the track is not occupied, the red lights shall be extinguished.


a) An indication to indicate the availability of the supply from the Mains/Diesel Generator/ Catenary 1 or 2 should be suitably indicated.


a) Approach track circuits where provided, for all directions shall be indicated on illuminated diagram. In continuous track circuit territory, the approach track circuits will cover all the track circuits in rear of the first stop signal up to the next signal in rear or up to the track circuit specified in the table of control for approach locking. An approach track circuit controlling calling on signal shall be indicated separately with a distinct mark.

b) Advance approach warning of trains if required shall be indicated on the panel in the form of flashing lights or other type of indication and audible bell warning to attract attention of Station Master. These visual and audible warnings shall stop as soon as the approach track circuits mentioned in Cl. 21.3.6(a) above are occupied or signals are taken 'OFF' for the train. It shall be possible to silence the audible warning by pressing a push button. This cancellation shall not apply to train approaching subsequently for which the push button must be pressed again.

c) Where required, failure of a signal lamp/route lamp shall light a red lamp on the panel and give an audible warning for the same. Such indication may cover group of signals. A common audible warning can also be provided for a group of signals. It shall be possible to silence the audible warning by pressing a push button. Such cancellation of audible warning shall not apply to subsequent failures for which the push button must be pressed again.

d) A red lamp indication showing that the crank handle is free and a white indication showing that the crank handle is in the locked position shall be provided on the control panel near the crank handle control transfer switch / button.

e) The respective signal lock indication (white light) shall start flashing when an emergency route cancellation is initiated, in an approach locked condition of the route. This indication will extinguish after a lapse of two minutes and cancellation of the route.

f) If push buttons are used on control panel, a buzzer to indicate that push button/push buttons has/have been left pressed may be provided.

g) Suitable indications for slots, gate control etc. shall be provided.

h) The panel indication lamps shall be operated by not more than 24V miniature type bulbs or light emitting diodes.

i) Return wires from indication lamps and relays shall be suitably bifurcated so that excessive current does not damage it. Any break in return wire shall not fail the indication/relay or give a wrong indication or pick-up a wrong relay.

j) When an approved electronic flasher relay other than Mercury type is provided, a flashing white indication shall be provided at appropriate corner of the operating panel to indicate to the operator the satisfactory working of electronic flasher relay.


21.4.1 General Circuit Requirements

a) Before designing the detailed circuits, route and point control tables showing approach locks, back locking, release overlaps, isolation, interlocking, dependence of signal aspect, grouping of crank handles and the condition for release of crank handles, route release, gate release etc. shall be drawn up and approved by the competent authority. Provisions of GR & SR shall be observed.

b) Signal circuits shall be so designed that the signal shall not change to a lesser restrictive aspect than intended one and route shall not be released because of fluctuations in power supply voltage or when the supply resume following its failure.

c) While designing signal circuits and equipment to be used in AC traction territory special precaution shall be taken according to provisions of Chapter XXII on "Special requirements of signalling in AC electrified areas"

d) Common return shall not be provided in vital circuits.

e) All external circuits shall be in cables.

f) Where relays other than 24V, 1000 ohm relay with metal to carbon contacts are used, the circuits shall be so designed that not more than 45 such contacts are used in series in a circuit.

g) The proving of back contacts of metal to metal relays should be done in the circuitry,

h) All new installations shall preferably be of route setting type interlocking.

21.4.2 Route setting and interlocking circuits for installations provided with route setting system.

The route setting and clearance of signal shall be with the following conditions:-

a) SM's key is In

b) The interlocking is free

c) Operate the point in the route including overlap and isolation, if any, to desired position.

d) The crank handle for all the motor operated points and keys for all the key-locked points in the route, overlap and isolation are locked and their control is not released.

e) Interlocked level crossing gates are closed against the road traffic in the route including overlap, if any.

f) The complete route including overlap and isolation, if any, is correctly set and electrically locked.

g) The track circuits in the route up to the next signal/dead end and its overlap, if any, are clear.

h) Slot if any, from other agency shall be received,

i) Stop signal ahead is not blank,

j) Clearing of signal.

21.4.3 Route setting and interlocking circuits for installations provided with "route setting by individual ' operation of point" system.

The route setting and clearance of signal shall be with the following conditions :-

a) The points in the selected route and if required in overlap and isolation are operated to required position by individual operation of switches or push buttons in conjunction with group push button.

b) Operation of entrance exit buttons/switches or one control switch clears the signal if-

i) SM's key is In

ii) The interlocking is free

iii) The points including hand operated points in the route including overlap and isolation if any, are set, locked and detected.

iv) The crank handle for all the motor operated points and keys for all the key-locked points in the route, overlap and isolation are locked and their control is not released.

v) All interlocked level crossing gates are dosed and closed against the road traffic in the route and overlap, if any.

vi) Slot if any, from other agency has been received.

vii) The track circuits in the route up to the next signal/dead end and its overlap if any, are clear.

viii) Stop signal ahead is not blank,

ix) Clearing of signal.

Note:-  i) For clearing calling on signals, proving of track circuits in the route and overlap is not required. Calling on signal shall detect all the points including interlocked level crossings in the route, which the main signal above it detects.

ii) For clearing of shunt signals the proving of berthing track circuits, points & LC gates in overlap are not needed. This applies to both the systems having route or non route setting facilities.

21.4.4 The interlocking between conflicting routes shall be achieved through route interlocking electric circuits.

21.4.5 Approach locking or dead approach locking shall be provided for all manual stop signals. Approach locking shall be continuously effective from the predetermined point on approach of the signal.

21.4.6 Controls on level crossings, ground frames, cabins, sidings etc., shall be suitably interlocked.

21.4.7 A white indication for block control on the last stop signal should be provided on control panel, where -

i) Section ahead is worked on Absolute Block System and control panel and block instrument are placed at different locations.

ii) Block working is by means of axle counter or track circuit.

21.5 Route Release Circuits

21.5.1 Complete route release including overlap shall be effective only after the signal governing the route is put back to 'ON' and corresponding route switch/button has been operated to normalize the route. Automatic route release by the passage of train and complete release of route through sequential route release shall be provided.

21.5.2 Where a route has got number of route sections, the circuit shall be so designed that the route section does not release only by picking up of the concerned track relay. Same is released only after the next track circuit is also dropped and picked up, except in case when the last track is a berthing track. In cases where the route is controlled by single track circuit, the route release shall be controlled after predetermined time delay.

21.5.3 The route release circuit shall be so designed that it will release only when at least two track circuits drop and pick-up in sequence.

21.5.4 In installations provided with route setting system, sectional route release shall be provided where required. In such cases sub-route section already released shall permit setting up of other routes, if interlocking otherwise permits.

21.5.5 In case of installations provided with non route setting system, sectional route release may be provided where considered necessary. The complete route release shall be effective only after the signal governing the route is put back to 'ON' and corresponding route switch/push button has been operated to normalize the route. However, where sequence proving relays are provided to prove the authorized passage of a train, automatic route release shall be provided.

21.5.6 It shall be possible to release a route in emergency after suitable time delay, with the approach track occupied, provided the train has not passed the signal during the time interval.

21.5.7 It shall be possible to release a route in emergency after a suitable time delay where a approach track circuits have not been provided and after the signal has been put back to danger provided the train has not passed the signal during this time interval.

21.5.8 When the route is released by the passage of train, the overlap points shall be released only after the lapse of two minutes of occupation of berthing track as well as clearance of last point track circuit of the route. On cancellation, the overlap points may be released simultaneously along with the main route.

21.5.9 Facility of emergency route/sub-route cancellation may be provided, where necessary. Every such cancellation shall be recorded on a counter and in a register to be maintained by traffic representative.

21.6 Signal Control Circuits

21.6.1 It shall not be possible for a signal to assume 'OFF' aspect in installations provided with route setting facility unless the route switches/buttons have been operated and relevant route has been correctly set and locked and relevant track circuits are clear. In installation provided with non route setting facility, the signal shall not assume 'OFF' aspect unless the route is set and locked, relevant track circuits are clear and signal switch/button has been operated. In case self restoring type of push buttons are used, signal shall not assume 'OFF' aspect unless push button is pressed and released.

21.6.2 Circuits shall be so designed that the failure of any part of a circuit affecting the control of the signal shall cause the signal to display a more restrictive aspect than the intended aspect.

21.6.3 The circuit shall be so designed that in case of failure of a signal lamp, the lamp of more restrictive is lit automatically and in case of failure of red lamp it shall not be possible to clear the signal in rear.

21.6.4 Fouling protection, approach locking, indication locking, route locking, siding control key locking, crank handle locking and track locking shall be incorporated in the relevant control circuits.

21.6.5 Each aspect light of a signal may be proved where necessary and the aspect indication shall be provided as per Para 21.3.3(b).

21.6.6 Wherever required, necessary control on the level crossing, ground frames, cabins, siding control key, crank handles etc. shall be provided.

21.6.7 The correspondence of the point control relays and point indication relays may be proved in signal circuits before the signal displays an 'OFF' aspect

21.7 Interlocking of level crossing gates

It shall not be possible for a signal to assume 'OFF' unless all interlocked level crossing gates in its route and overlap are closed and locked against the road traffic. Similarly, it shall not be possible to release any such interlocked gate until the signal is replaced to 'ON' position and the route up to the gate is released.

21.8 Point Interlocking and control circuits

21.8.1 The points once set shall remain in the last operated position until these are operated by different route setting or by individual operation of points. However, isolation points of catch siding, slip siding may operate automatically after the passage of train to their isolation position where sectional route release is provided.

21.8.2 Operation of points shall be possible only when the interlocking is free and relevant point track circuit is clear. Emergency operations, where provided when point zone track circuit fails, it shall be possible to operate the concerned point provided interlocking is free by releasing an emergency control. Each such operation shall be recorded on a counter.

21.8.3 Interlocking between points shall be provided only to the minimum extent necessary.

21.8.4 Point control circuits shall be so designed that a cross connection or a short circuit can not operate a point or give a false indication of the same.

21.8.5 Crossovers shall be operated by separate point machines, one at each end. The detection of setting and locking of the points at the two ends of a crossover shall be connected in series.

21.8.6 Crank handle / point NX key provided for manual operation of the points worked by electric point machine must be interlocked with signals.

21.8.7 It must not be possible to release the crank handle/point NX key unless the signals have been put back to 'ON' position and concerned route is released. However, if the route remains locked due to what so ever reason, it shall be possible to release the crank handle/point NX key after a time delay of 120 seconds from the time the signals have been put back to 'ON' position at a station where crank handle is kept in location near the concerned points. In case of stations having crank handle in SM's office, it shall be possible to release the crank handle as soon as the signal is put back to 'ON' and crank handle release command is given.

21.8.8 In major yard where number of points are more, these points should be grouped in different zones maintaining the yard flexibility. The crank handle/point NX key for each group of point machines should be so arranged that they can not be interchanged.

21.8.9 Siding control key for manual operation of siding points, taking off from running lines, shall be so interlocked that it may not be possible to clear the signal leading over to that line when the key is released for operating siding points for shunting purposes.

21.9 Cross Protection

21.9.1 For purely internal circuits including vital circuits, double cutting or cross protection may not be provided unless specifically required.

21.9.2 All equipments in external circuits shall be suitably protected from cross connections and rendered immune to false operation by stray currents/induced voltages.

21.10 RELAYS

21.10.1 The various type of relays used in relay interlocked systems shall be of approved type and conform to appropriate specifications as detailed in Para 8.13 Chapter VIII unless otherwise specially permitted.

21.10.2 Time element relays of approved type shall be used. Where approved electronic time element relays are used, these shall be two in number and their contacts shall be in series in the concerned time release circuits.

21.10.3 The relays, including track relays, located in the track side location boxes, shall be preferably plug-in type.

21.10.4 All plug-in relays and relay groups shall be fitted with non-interchangeable interlocking device to prevent the wrong relays/relay group being accidentally plugged-in during replacement.

21.10.5 Removal or replacement of plug-in relays/relay groups from the relay racks during operation shall not cause any unsafe conditions in the circuits.

21.10.6 As far as possible, all relays shall be housed in the relay room of the controlling cabin to achieve maximum centralization.

21.10.7 Where feasible all relays except track relays, shall have 10% of working contacts as spare subject to a minimum of one front and one back to facilitate addition and alteration to the circuits at a later date. Extra space to accommodate repeater relays shall be provided in the relay rack to cater for future expansion.

21.10.8 Mercury type or any other approved type flasher shall be used.

21.10.9 Sequential proving of front and back contact shall be ensured where metal to metal contact relays are provided.

21.10.10 All relays, relay groups shall be sealed.


21.11.1 The main running signals shall be of multi unit colour light type.

21.11.2 Shunt signals shall be of position light type.

21.11.3 Route indicators shall be either of the direction type or multi lamp unit type or of stencil type conforming to approved design.

21.11.4 'A' marker lights for semi-automatic signals shall be of approved type.

21.11.5 Roundels, glasses and lenses used in the colour light signals shall be of approved type.

21.11.6 The signal lamps used for different types of signals shall be of approved type.

21.12 POINTS

21.12.1 Electrical point machines shall be of an approved type and conform to appropriate specification indicated in Chapter VIII Para 8.13 unless otherwise, specially permitted.

21.12.2 Means shall be provided to cut off the motor feed in case of obstruction to the point movement after a predetermined time lag, based on the type of point machine used.

21.12.3 The point operating control circuits shall have track circuit control, overload protection and cross protection.

21.12.4 Hand worked point switches shall be equipped with circuit controllers that are operated by the switches when closed. Keys controlling such switches shall be electrically locked by the approach/time/back locking track circuit so that it's not possible to work them in the face of an approaching train.

21.12.5 The crank handles shall be provided to facilitate operation of points in case of failure of point machines. For this purpose, if necessary, the points in the yard may be divided into convenient groups and to distinguish particular groups, crank handles with different wards shall be used. The crank handles may be provided in a suitable place near the group of points to which they refer. The slots in the point machines provided to take the crank handles would also be suitably made to take only the crank handle applicable to the group. The crank handles shall, however, normally be locked. It shall be possible to release them for use in point machine by releasing a control from the panel. With the crank handle released, it shall not be possible to set up any of the relevant routes and clear the signal for the same. The interlocking of crank handle can also be achieved by using NX key of different wards.

21.12.6 In AC traction area, the point machine shall be immune to the effects of Electro-magnetic induction. These should be installed within the range to which these are immune to the effects of AC electrification.


21.13.1 Provisions of chapter on track circuits shall be generally followed.

21.13.2 Track circuits of an approved design shall be used unless otherwise specially permitted.

21.13.3 Axle counters of an approved design can be used in lieu of track circuits.

21.13.4 The track circuits shall be so designed and installed that in the case of a failure of block joints, the adjacent track circuit feed shall not wrongly energize the next track circuit relay.

21.13.5 A DC track circuit shall not be fed directly from AC supply using transformer and rectifier. A storage battery must be connected with battery charger and the connection is so made that if battery is disconnected the battery charger is also disconnected.

21.13.6 DC track relays can be centralized in location/relay room only by using separate 2 core cable of adequate cross section and not through multi-core cables.

21.13.7 At stations where points and signals are operated from an Assistant Station Master's office at a central place, track circuiting of the entire station section including all lines where direct reception is provided shall be done.

21.14 CABLES

21.14.1 Provisions of chapter on Cables & Overhead lines shall be generally followed.

21.14.2 At least two cores of cable shall be provided between two ends of the yard to cater for telephone communication for maintenance purposes in non RE areas. Where the yard is extending over a large area, the location boxes may be grouped and one socket may be provided in one of the location boxes in the group so that telephone communication are conveniently available for co-ordination with the cabin during maintenance or rectification of failures of various ground equipments. Where such groups are situated in different directions from the cabin, a separate pair of conductors shall be used for each direction connected to the cabin. In RE area, provision shall be made for telephone communication through a telecommunication cable if already available or a separate telecom cable shall be laid for the purpose.

21.14.3 Earth leakage detectors of approved type may be provided to detect any leakage to earth in cable conductors.


21.15.1 The wiring used in various equipment shall comply with the requirements laid down in IRS specification No. S 23.

21.15.2 All wiring in the cabin and locations shall be done in a neat manner so that the wiring does not in any way prevent the proper functioning over working parts and is easily accessible for maintenance.

21.15.3 All wiring in the cabin and location shall be terminated on approved type terminal blocks/tag blocks unless otherwise specially permitted.

21.15.4 At all locations and cabins, wire entrance of adequate size, conveniently located for ease of approach to terminals and other equipment so arranged as to protect the wires from mechanical injury, shall be provided. Such wire entrance shall be plugged and sealed with suitable compound after the wiring is completed.

21.15.5 The internal wiring of relay rack in locations and cabin shall be generally carried out with plain annealed copper conductors; PVC insulated unarmoured flame retarding type of 1100V grade unless otherwise specially permitted. The size of the conductors can be as follows:-

i) Single core size                                   -          1 mm

ii) Multi core each core of size                   -          1 mm

iii) Multi core each core of size                  -           0.6 mm

iv) Flexible insulated wire size                    -           16/0.20 mm

v) Flexible multi-strand wire size                 -           3/0.737 mm

21.15.6 Rack to rack wiring shall be generally carried out with multi core cable having plain annealed copper single core conductor of size 1/0.6 mm or multi-strand 16/0.2 mm as per approved specification for indoor cables.

21.15.7 Following practice shall be adopted for internal wiring. The connecting wires shall be terminated on eyelets/lugs/receptacles unless otherwise specially permitted.

a) All connections to plug-in non-proved type relays flexible wire of 16/0.20 mm shall be used.

b) All connections to proved typed relays shall be done with 0.6/1 mm single strand multi core cable.

c) For all connections from cable terminations to tag blocks and indicators etc. shall be done with the help of 1 mm single strand wires.

d) For all connections to circuit breakers, lever locks etc. single strand wire of 1.5/1.6 sq. mm size shall be used.

21.15.8 Relay to Relay wiring on the same rack should be as far as possible direct without intermediatries like tag block/terminals.

21.15.9 Identification Marker for identifying the terminals and tags shall be provided to each terminal to identify the circuits for which it is used.

21.15.10 Relay racks shall have sufficient capacity to take additional equipment to the extent of 15% of equipment provided to permit additions and alterations.

21.15.11 Charts showing the position of relays on relay racks and contact analysis of relays indicating the spare and used contacts shall be prepared and kept in the relay room.

21.15.12 For future expansion, provision shall be made to accommodate additional relays, relay groups & racks in the relay room.


21.16.1 Cartridge type fuses shall preferably be of N.D. type. Where screw cap cartridge type fuses are used, these shall be of different colour codes for different current rating and these shall be non - interchangeable.

21.16.2 Fuses shall be so grouped that blowing of a fuse has minimum repercussion on train operation.

21.16.3 The fuses when blown off, shall preferably give a visual indication .

21.16.4 Each group of circuits shall be carefully protected by fuses in the cabins and in location to facilitate easy fault localization.

21.16.5 Fuses shall be so arranged that they can be easily replaced without causing interference or unsafe conditions to other circuits.

21.16.6 Cartridge fuse links shall be approved type.

21.16.7 The terminal block and tag blocks shall be of approved type unless otherwise specially permitted.

21.16.8 The terminal boards provided at the locations and other places shall be provided with suitable links to facilitate isolation of the two sides of the circuits which are connected through the terminal links.


The power supply arrangements shall be as per details given in Chapter XVI on "Power Supply Arrangement".


21.18.1 In case of big yards and busy stations where a large number of trains/ shunting movements take place resulting in intensive relay operations, relay room shall be air conditioned .

At way side stations where the traffic density is less, the provision of air conditioning is optional.

Relay rooms in areas which are prone to dust or in vicinity of chemical factories releasing injurious fumes or in areas with extreme temperature may be air conditioned.

21.18.2 Fire fighting equipment shall be kept in the power supply equipment room. At major installation fire detection and alarm shall preferably be provided in the relay room of relay interlocking installations.

21.18.3 Suitable standard earthing shall be provided for all operating panel, power supply, switch board, transformers, inverters etc.

21.18.4 At all Relay Interlocking Installations, Data Logger shall be provided.

21.18.5 Communication between the SM's panel room, relay room, equipment room and locations shall be provided.

21.18.6 Panel shall be operated by Station Master/Panel Operator who shall possess a panel competency certificate issued jointly by Traffic Inspector and Section Engineer (Signal) of the section duly countersigned by assistant officer of Traffic and Signal Department.


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