80 Questions
At what temperature should the insulation resistance of a signal cable be measured?
Buried temperature
What is the minimum distance required from the centre of the nearest Track when digging cable trenches with O.H.E structures along the cable route?
5.5 meters
What should be bonded to earth during insulation resistance testing?
Metallic sheath or metal work
What is the minimum insulation resistance required per km for a signal cable?
5 mega ohms
What is the recommended voltage for insulation testing of signalling cables?
500 V
Why should all cores of a cable be disconnected at both ends during insulation testing?
To isolate the cable for testing
What should be done if the insulation resistance of a signal cable is found to be lower than 5 mega ohms per km?
Investigate the cause and repair or replace the cable
Why should galvanized iron metallic pipes be prohibited near switching stations or traction masts?
To prevent electrostatic discharge
When is it recommended to test the insulation of signalling cables?
Once in three years, if cables are monitored through ELD, else annually before monsoon
Why is it essential to short or earth the conductors of the cables before and after testing?
To prevent electrostatic discharge and ensure safety
What is the purpose of recording the results of insulation resistance tests?
To monitor the trend of deterioration of the cable insulation over time
What should be done with the test results of insulation resistance tests?
Record them in an approved proforma
What is the recommended frequency for testing the insulation of tail cables?
Once a year
Why is it important to test the insulation of cables in dry weather?
To ensure the accuracy of the test results
What should be done if a sudden fall in insulation is observed?
Investigate the cause and take immediate steps to repair or replace the cable
Why is safety a critical consideration during cable testing?
To prevent electrostatic discharge and ensure safety of personnel and equipment
What is the primary purpose of conducting random tests in wet weather?
To identify sudden deterioration in insulation of cables.
What is the purpose of providing an Earth Leakage Detector (ELD) in signalling installations?
To provide remote monitoring of cable conditions.
When should the first measurement of insulation of the cable be carried out?
After laying of the cable.
What is the recommended action when moisture or water leak is detected in cable termination devices?
Immediate attention to find the source of the leak.
What is the purpose of regularly inspecting protective works at track crossings, culverts, and bridges?
To ensure the safety of existing cables.
When should cables be meggered afresh?
After major work in a yard.
Why is it necessary to have a representative of the signal and telecommunication department present during excavation?
To ensure the safety of the existing cables.
What is the purpose of keeping cable termination devices, pillar boxes, cable heads, and glands clean and dry?
To prevent moisture or water leak.
What is the primary reason for visually inspecting the cable before laying it in the trench?
To ensure there is no damage to the cable before laying
What should be maintained after testing the cable for insulation and continuity of the cores?
A record of insulation and loop resistance
Why is it essential to ensure no kink is formed while paying out the cable?
To prevent damage to the cable during laying
What should be done if the cable drum is in a damaged condition?
Use a horizontal revolving platform to pay out the cable
Why should the cable not be dragged on the ground for laying purposes?
To prevent damage to the cable due to dragging on the ground
Who should supervise the work when mechanized equipment is used?
SSE/JE (Signal) in charge of the work
What is the purpose of testing the cable for insulation and continuity of the cores?
To verify the cable's electrical integrity
Why should cable drums be stored in a covered shed?
To protect the cable from direct exposure to the sun
What is the minimum separation required between signalling cables and HT power cables?
3 meters
In which order should cables of different categories be laid in the same trench, starting from the main track side?
Telecommunication cable, Signalling cable, Power cable
Why should signalling cables not be laid above ground?
To prevent mechanical damage
What precaution should be taken when laying signalling cables in station yards?
Laying cables in ducts
How should cable supports be spaced to avoid sagging?
Close together to prevent sag
What is the recommended minimum distance from the centre of the nearest track for laying cables outside the station section?
5.5 meters
What is the purpose of laying cables in trunking/duct/pipe when taking them between the tracks?
To provide protection and safety
How should indoor signalling cables be laid?
On ladders or channels
When digging trenches for cable laying, what is the minimum distance recommended from the centre of the track?
3 meters
What should be used to mark the route of the cable at suitable intervals and at diversion points?
Cable markers
What method should be used to cross the track when laying cables?
Horizontal directional drilling method
What type of pipes should be used when crossing small culverts with low flood levels?
GI/DWC-HDPE pipes
What should be done to the soil excavated from the trench after laying the cables?
Put it back on the trench, rammed and consolidated
What should be used to firmly hold the cables at the Cable room/Relay room/apparatus case?
Suitable clamping arrangement
What should be avoided when crossing the track with cables?
Crossing the track under points and crossings
What should be provided for the cables inside the Cable room/Relay room?
All of the above
In what type of areas can cables be laid at a depth of 1.2 meters with anchoring at every 10 meters?
Theft prone areas
What is the recommended distance between cables of other departments and signalling cables?
10 cm
What type of pipe should be used while laying the cable for protecting it?
Half Cut DWC-HDPE pipe
Why should cables belonging to other departments not be laid in the same trench along with Signal & Telecommunication cables?
To prevent interference between cables
What should be done to prevent/minimise damages to cable by any other future digging activities in the vicinity?
Use of ducts with suitable covers
What should be considered when laying cables in rocky areas?
The protection of the cable as shown in Drg.No: 15-D2
What should be done to cables when laying them in areas where a number of other utilities may be existing?
Special precautions should be taken
What should be used to prevent water collection in the duct?
Ducts with suitable covers
Why is it necessary to short or earth the conductors of the cables before and after testing?
To discharge any accumulated electrostatic charge
What is the purpose of recording the results of insulation resistance tests in an approved proforma?
To monitor the trend towards deterioration of the cable over time
What should be done if a sudden fall in insulation resistance is observed during testing?
Investigate the cause and take corrective action
Why is it important to test the insulation of signalling cables in dry weather?
To reduce the risk of moisture affecting the test results
What is the recommended frequency for testing the insulation of tail cables?
Once a year
Why is it essential to ensure that no unsafe conditions are set up by the application of test equipment?
To prevent electrical shock to personnel
What is the purpose of an Earth Leakage Detector (ELD) in signalling installations?
To detect earth leakage faults in the cables
Why is it important to record the results of insulation resistance tests in a specific format?
To facilitate comparison of test results between successive tests
What is the primary consideration for conducting insulation resistance tests on signal cables?
To ensure the safe operation of trains is not affected
Why are galvanized iron metallic pipes prohibited near switching stations or traction masts?
To reduce the risk of electrical interference
What is the purpose of bonding metallic sheaths or metal work to earth during insulation resistance testing?
To reduce the risk of electrical shock
What should be done to the conductors of a cable before insulation resistance testing?
They should be disconnected at both ends
What is the purpose of using a 500 V insulation tester for signalling cables?
To measure the insulation resistance of the cable
Why should cables be laid at a minimum distance of 5.5 meters away from the centre of the nearest Track?
To prevent damage to the cables from train operations
What is the purpose of using an Earth Leakage Detector (ELD) in signalling installations?
To detect earth leakage faults in the signalling system
Why should signalling cables not be laid above ground?
To prevent damage to the cables from environmental factors
What should be done to avoid damage to the protective battens of the cable during transportation?
Avoid rolling the cable drum over objects that could cause damage.
Why should cable routes be planned on a route plan showing existing routes of power cables, etc.?
To avoid crossing over power cables
What should be done to the cable drums when they are not in use?
Place suitable stoppers for stability
Why should separate cables of suitable size be laid for point operation?
To ensure that the cables are not damaged during point operation
What should be incorporated in the bridge design for laying cables on bridges?
Suitable ducts or pipes
Why should the cable drum not be dropped on the ground directly during unloading?
To avoid damage to the cable
What should be avoided when laying cables in station yards?
Laying cables above ground
Why should the cable route plan be approved by Engineering and Electrical departments?
To ensure that the cables are laid safely and efficiently
Study Notes
Safety Precautions
- Ensure no unsafe conditions are set up by the application of test equipment
- Conductors in signalling cables must be tested for their insulation before commissioning
- Conductors may accumulate electrostatic charge, so short or earth them to discharge the accumulated charge
- Record insulation resistance test results in an approved proforma
- Compare test results between successive tests to determine cable deterioration trend
Testing of Cables
- Test all conductors in signalling cables for insulation every 3 years in dry weather, or annually if not monitored through ELD
- Test tail cables for insulation annually
- Compare test results to determine trend towards cable deterioration
- Investigate and repair/replace cables if a sudden fall in insulation is observed
Cable Installation and Maintenance
- Keep cable trenches at least 5.5 meters away from the centre of the nearest track where O.H.E structures are present
- Prohibit the use of G.I pipes or metallic pipes within 300 meters of a feeding post
- Bond metallic sheaths or metal work to earth during testing
- Disconnect all cores of a cable at both ends before testing
Insulation Resistance Testing
- Use a 500V insulation tester for signalling cables and 100V for Quad cables
- Ensure conductors, cables, and insulated parts are clean and dry during testing
- Connect one terminal of the tester to the conductor under test and the other to all other conductors and earth
Additional Testing and Maintenance
- Perform random tests in wet weather if necessary to localise any sudden deterioration in insulation
- Keep cable termination devices, pillar boxes, cable heads, and glands clean and dry
- Frequently inspect these parts for moisture or water leaks
- Provide Earth Leakage Detectors (ELD) in signalling installations and interface with Datalogger for remote monitoring
Cable Laying and Storage
- Separate signalling cables from LT power cables by a row of bricks or other approved means
- Maintain a minimum 3-meter separation from HT power cables
- Lay cables in a specific order in the same trench: Telecommunication cable, Signalling cable, Power cable
- Lay signalling cables in ducts in station yards and protect them from mechanical damage
- Store cable drums in covered sheds to protect against direct exposure to sun
Laying of Cables
- Cables should be laid at a distance of not less than 3 meters from the center of the track, with the width of the trench being outside the 3 meters distance.
- The soil excavated should be put back on the trench, rammed, and consolidated after laying the cables.
- Cable joints of approved type should be used, and cable markers of approved type should be provided at suitable intervals and at diversion points to mark the route.
Cable Crossing
- When a cable has to cross the track, it should be ensured that the cable crosses the track at right angles and does not cross under points and crossings.
- The cable should be laid in concrete/GI/DWC-HDPE pipes or in any other approved manner while crossing the track.
- Wherever feasible, horizontal directional drilling method may be used.
Testing of Cables
- All conductors in signalling cables must be tested for their insulation in dry weather once in three years, provided cables are monitored through ELD, else annually.
- Testing should be done before the monsoon season as per instructions specified in section 4.
- Reading should be recorded as per the format mentioned in Annexure: 15-MS1.
- A comparison of the test results between successive tests carried on a cable under similar conditions will give an indication of the trend towards deterioration of the cable.
Cable Safety
- The conductors of the cables may accumulate electrostatic charge, and the cable conductors should be shorted or earthed to completely discharge any accumulated charge.
- This should be done before connecting the insulation tester while commencing the test and after the insulation tester is disconnected when the test is completed.
Insulation Resistance Testing of Signal Cables
- The insulation resistance tests should be made when conductors, cables, and insulated parts are clean and dry.
- A 500 V insulation tester should be used for insulation testing of signalling cables, and 100 V insulation tester shall be used for Quad cables.
- Any metallic sheath or metal work of any rack or apparatus case should be bonded to earth during the test.
Cable Route Planning
- Cable route plan should be approved by Engineering and Electrical departments.
- Approval of S&T open line is also required where ever it is prepared by other than open line.
- In case of Construction works, cable route plan shall be signed by Engineering and Electrical departments of executing agencies as well.
Cable Storage and Transportation
- Cable drums should not be stacked on flat side, and suitable stoppers should be placed for stability.
- Cable drums should have access for lifting and moving.
- When rolling the cable drum, the drum should always be rotated in the direction of the ‘arrow’ which is marked on the drum.
This quiz covers the safety precautions and testing procedures for electrical cables, including insulation testing and electrostatic discharge prevention.
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