Telecommunications Cabling Quiz
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Questions and Answers

What color is paired with the Green main color in Pair 3?

  • White (correct)
  • Yellow
  • Red
  • Black

    • Which of the following pairs constitutes a 100 pair cable?

  • 2 units of 50 pair units
  • 5 units of 20 pair units (correct)
  • 5 units of 10 pair units
  • 10 units of 10 pair units

    • In the colour code scheme, which main color is assigned to Pair 10?

  • Blue
  • Green
  • Grey (correct)
  • Brown

    • What material is used for jacket insulation of the armored cable?

    <p>Polythene</p> Signup and view all the answers

    Which pair combination consists of a main color of Orange and a mate color of Black?

    <p>Pair 12</p> Signup and view all the answers

    Which colors are classified as main colors in the cable colour code scheme?

    <p>Blue, Orange, Green, Brown, Grey</p> Signup and view all the answers

    How many units are there in a 20 pair cable?

    <p>4 units</p> Signup and view all the answers

    Which color is the mate for the Blue main color in Pair 1?

    <p>White</p> Signup and view all the answers

    What is the primary purpose of twisting the wires in paired cables?

    <p>To reduce electrical interference</p> Signup and view all the answers

    Which type of cable is compatible with indoor extension applications?

    <p>Switchboard cables</p> Signup and view all the answers

    What is the role of a ground shield in paired cables?

    <p>To prevent high frequency noise</p> Signup and view all the answers

    How do twisted pairs help eliminate crosstalk between adjacent circuits?

    <p>By balancing the electrical potential</p> Signup and view all the answers

    What diameter options are available for conductors in switchboard cables?

    <p>0.4mm, 0.5mm, 0.63mm</p> Signup and view all the answers

    Which standard is associated with underground PIJF cables?

    <p>IRS:TC 41/97 (Amd. 2)</p> Signup and view all the answers

    Which application does not utilize paired telephone cables?

    <p>Video surveillance systems</p> Signup and view all the answers

    What effect does the twisting of conductors have on the net induced voltages?

    <p>It keeps voltages the same on both conductors</p> Signup and view all the answers

    What is the effect of capacitance coupling in an electric conductor insulated from earth?

    <p>It charges the conductor to a potential with reference to earth.</p> Signup and view all the answers

    What role do the rails play in the return of currents flowing in the catenaries?

    <p>They provide an alternate path for the currents back to the feeding point.</p> Signup and view all the answers

    How does the catenary system interact with parallel conductors?

    <p>It acts like a primary winding inducing a secondary current.</p> Signup and view all the answers

    What hazardous effect does inductive interference have on telecommunication circuits?

    <p>It causes induced voltages that can interfere with signaling arrangements.</p> Signup and view all the answers

    Which of the following descriptions applies to the source of alternating magnetic fields in the context described?

    <p>The currents flowing in the catenaries.</p> Signup and view all the answers

    What is a potential consequence of the harmonic components of the catenary currents?

    <p>They cause unworkable telecommunication circuits.</p> Signup and view all the answers

    What phenomenon occurs due to the proximity of AC traction to communication cables?

    <p>It induces an e.m.f. in cable sheaths and conductors.</p> Signup and view all the answers

    What challenge does induced emf in cable sheaths pose to workers and equipment?

    <p>It creates a significant safety hazard.</p> Signup and view all the answers

    What is the maximum longitudinally induced voltage in telecommunication circuits during the normal functioning of a power line?

    <p>60V</p> Signup and view all the answers

    What induced voltage should not be exceeded during a traction power line short circuit condition?

    <p>430V</p> Signup and view all the answers

    What screening factor should be achieved with cables laid along the tracks?

    <p>0.1</p> Signup and view all the answers

    What value of psophometric voltage in communication circuits is deemed acceptable?

    <p>2mV</p> Signup and view all the answers

    What happens when cable is in close proximity to strong electromagnetic fields?

    <p>Induced unwanted current and voltage</p> Signup and view all the answers

    How is psophometric voltage typically measured?

    <p>Using a psophometric meter</p> Signup and view all the answers

    What precaution can be taken to prevent cumulative build-up of induced voltages in communication circuits?

    <p>Introducing isolating transformers every 17 km</p> Signup and view all the answers

    What is the implication of excessive electromagnetic interference (EMI) in data communication?

    <p>Increased errors and packet retransmissions</p> Signup and view all the answers

    What is the contour allowance when calculating cable requirements for a route length of 10 km?

    <p>0.25 km</p> Signup and view all the answers

    How much cable reserve is required for each LC gate?

    <p>3 meters</p> Signup and view all the answers

    What is the total cable length required for a block section with a route length of 10 km, including all necessary allowances?

    <p>10.55 km</p> Signup and view all the answers

    What is the required cable loop length for minor bridges in the given cable requirement calculation?

    <p>5 meters on each side</p> Signup and view all the answers

    Which of the following lengths must be added for cable approaches towards major bridges?

    <p>10 meters on each side</p> Signup and view all the answers

    When laying cables in major yards and stations, how is the main cable typically arranged?

    <p>In a zigzag way</p> Signup and view all the answers

    How much cable loop is required for the joints if there are 10 joints in the section?

    <p>0.20 km</p> Signup and view all the answers

    What is the distance requirement at each track or road crossing?

    <p>2.5 meters on each side</p> Signup and view all the answers

    What is the minimum distance that the cable must be laid away from any metallic part of the OHE?

    <p>1 meter</p> Signup and view all the answers

    How often should RCC cable markers be provided on the cable route?

    <p>Every 50 meters</p> Signup and view all the answers

    What color should be used for cable markers placed at joint locations?

    <p>Green</p> Signup and view all the answers

    What is the recommended horizontal clearance for telecom cables near power cables of 11KV and above?

    <p>At least 0.6 meters</p> Signup and view all the answers

    What must be done whenever laying new telecom cables across or parallel to existing high voltage power cables?

    <p>PTTC approval is mandatory</p> Signup and view all the answers

    What happens if there is an absence of sheath continuity and armor continuity in Telecom cable near power cables?

    <p>AC induction occurs</p> Signup and view all the answers

    What is the preferred length of RCC pipes for laying cables on either side of the feeding point?

    <p>300 meters</p> Signup and view all the answers

    Who is responsible for the joint inspection after completion of cable laying works?

    <p>Both SSE/JEs of Open Line and Concerned Organisation</p> Signup and view all the answers

    What is the maximum permissible longitudinally induced voltage for safety in telecommunication cables near 25 KV AC traction?

    <p>150 V</p> Signup and view all the answers

    What screening factor is indicative of the effectiveness of Aluminium Sheathed/Screened cables?

    <p>0.1</p> Signup and view all the answers

    At what distance must isolation transformers be provided to ensure safety from induced voltage?

    <p>17 Km</p> Signup and view all the answers

    Which of the following is considered a safe working voltage without special precautions?

    <p>60 V</p> Signup and view all the answers

    What is the effect of running telecommunication circuits parallel to 25 KV AC lines?

    <p>Potential increase in induced voltage</p> Signup and view all the answers

    What should be considered when crossing tracks with telecommunication cables?

    <p>Run underground cables at right angles</p> Signup and view all the answers

    Which protective measures are necessary for telecommunication lines entering equipment rooms?

    <p>Provision of G.D tubes, fuses and earthing</p> Signup and view all the answers

    What happens if induced voltage on cable pairs exceeds 150V AC?

    <p>Safety risks for personnel and equipment</p> Signup and view all the answers

    What is the minimum insulation resistance required for conductors when tested with a 500 V megger?

    <p>5000 Mega ohms per kilometre</p> Signup and view all the answers

    What type of material is used for the intermediate sheath that provides additional protection to the screening in a telecom cable?

    <p>Polyvinyl Chloride (PVC)</p> Signup and view all the answers

    Which component applied over the cable core is specifically designed to prevent oxidation of the aluminum screen?

    <p>Woven tape impregnated with barium chromate</p> Signup and view all the answers

    What is the direction of the lay of the armouring compared to the outermost layer of screening?

    <p>Opposite direction</p> Signup and view all the answers

    What ensures that the insulation of the conductors is applied correctly?

    <p>Insulation must be applied closely and homogeneously</p> Signup and view all the answers

    What describes the screening factor, K, in the context of induced voltages in conductors?

    <p>K is the ratio of induced voltage with a sheath to that without it.</p> Signup and view all the answers

    Why is the screening factor typically less than unity?

    <p>Induced voltages in sheaths are generally lower than those without sheaths.</p> Signup and view all the answers

    What condition must a metallic sheath satisfy to provide effective screening?

    <p>The sheath must carry a return current.</p> Signup and view all the answers

    How does an insulated sheath affect the voltage between the core and the sheath?

    <p>The voltage between them becomes zero.</p> Signup and view all the answers

    What characteristic makes paper a suitable insulator in RE cables designed for long-distance communication networks?

    <p>It is a very good insulator.</p> Signup and view all the answers

    What is the consequence of not earthing both ends of the sheath?

    <p>The sheath will not effectively reduce core to earth voltage.</p> Signup and view all the answers

    Which type of cable has been largely phased out and replaced due to its limitations in bandwidth?

    <p>RE cables</p> Signup and view all the answers

    What principle is described when talking about the induced voltage in cable conductors?

    <p>Induced voltage is developed due to the difference of primary and secondary magnetic fluxes.</p> Signup and view all the answers

    Which specifications are used for the introduction of 4 quad/6 quad cables for long-distance applications?

    <p>RDSO/SPN/TC/72/07</p> Signup and view all the answers

    What impact do current-carrying sheaths have on the magnetic field?

    <p>They create an opposing field that reduces induced voltage.</p> Signup and view all the answers

    What is the primary component of the conductor used in polythene insulated cables?

    <p>Plain annealed high conductivity copper</p> Signup and view all the answers

    What does the I.T.U-T recommend regarding induced voltages?

    <p>They provide guidelines on permissible voltages and protective measures.</p> Signup and view all the answers

    What is the role of PVC insulation in PIJF quad cables?

    <p>To offer moisture and abrasion resistance</p> Signup and view all the answers

    Which of the following applications utilize PVC insulated quads in their configuration?

    <p>Block Signaling Applications</p> Signup and view all the answers

    What is a primary disadvantage of RE cables compared to OFC networks?

    <p>Lower data transmission capacity</p> Signup and view all the answers

    What functions has been transitioned to the OFC network from the existing signaling circuits?

    <p>All of the above</p> Signup and view all the answers

    In a 6-Quad cable, which color is assigned to the A-Wire of Quad 5?

    <p>Yellow</p> Signup and view all the answers

    What is the characteristic impedance of the unloaded 4-Quad cable at 800 Hz?

    <p>470 Ohms</p> Signup and view all the answers

    Which color is associated with the quad whipping for Quad 4 in both 4-Quad and 6-Quad cables?

    <p>Grey</p> Signup and view all the answers

    What type of conductor insulation color is used for the B-Wire of Quad 3 in a 4-Quad cable?

    <p>White</p> Signup and view all the answers

    Which of the following pairs consists of the first and second wires of a pairing in a quad cable scheme?

    <p>A-Wire and B-Wire</p> Signup and view all the answers

    Looking at the specifications, what is the maximum impedance for the 6-Quad cable when loaded?

    <p>1120 Ohms</p> Signup and view all the answers

    Which wire color is used for the D-Wire in Quad 1 of both the 4-Quad and 6-Quad cables?

    <p>Grey</p> Signup and view all the answers

    What material is used for holding the quad together in PIJF Quad cables?

    <p>Open helical whipping of nylon yarn</p> Signup and view all the answers

    What should be used for new railway projects for control communication on identified routes?

    <p>24 Fibers Optical Fiber Cable with 6 quad cable</p> Signup and view all the answers

    Which of the following describes the allocation difference when laying 6 quad cable with and without Optical Fiber Cable?

    <p>Both allocations have 1 for Block Circuit and 3 for Emergency Control</p> Signup and view all the answers

    What is a significant characteristic difference between PIJF underground paired cables and quad cables?

    <p>Quad cables consist of more conductors than paired cables</p> Signup and view all the answers

    When should existing telecom cables be replaced by Optical Fiber System with 6 quad cable?

    <p>On the basis of age cum condition</p> Signup and view all the answers

    What is the configuration for existing overhead telecommunication systems on specified railway routes?

    <p>6 quad cable with OFC</p> Signup and view all the answers

    Which circuit is allocated to Quad No. 3 in the cable specification?

    <p>Emergency Control</p> Signup and view all the answers

    What needs to be considered for the replacement of existing telecom cables based on their alignment?

    <p>Should follow the same route configuration without changes</p> Signup and view all the answers

    Which of the following correctly lists the quad cable allocations when NOT combined with Optical Fiber Cable?

    <p>1 - Block Circuit, 2 - Section Control, 3 - Spare</p> Signup and view all the answers

    Study Notes

    Telecom Cables (Copper)

    • Indian Railways uses different telecom networks for voice and data communication
    • These networks use various types of copper cables with RDSO specifications
    • Cable types depend on administrative (e.g., telephone exchanges, Railnet) and train operation (e.g., block signaling, emergency communication) needs
    • Aerial lines (overhead lines) using Gl wires and ACSR currently being replaced by 6 Quad Underground Cables for section control and block communication
    • Micro-wave (MW) systems, both analog and digital, were used for radio patching (control communication) and long-distance administrative trunk circuits, but these are being replaced by OFC cables
    • Underground 4/6 Quad cables are used with OFC for many zonal railways as standalone or with OFC for improved communication and safety
    • Leaky Coaxial Cables are used in tunnels for seamless communication
    • Overhead lines are prone to faults due to natural calamities and human interference
    • They are less reliable for telecommunication circuits in electrified areas due to induced voltages from 25KV overhead lines
    • Overhead lines have a limited maximum number of pairs per pole

    Paired Telephone Cables

    • Twisted wire pairs are used to reduce electrical interference between pairs
    • Ground shield is used to prevent high frequency noise
    • Parallel pairs experience higher pickup voltages in the wire closer to the interference source
    • Twisted pairs reduce interference by alternating high and low voltages in both wires

    Underground PIJF Cables

    • Widely used in railways for local loops and networks, due to ease of installation and maintenance
    • Polythene-insulated, polythene-sheathed, jelly-filled cables, with Poly-Al moisture barrier
    • Colour code schemes for conductors are used for identification
    • Various sizes (10, 20, 50, 100, 200 pairs) of cables are available, with differing conductor diameters (0.5mm, 0.63mm)
    • Jelly filling in the cable prevents water ingress and protects cable core
    • The use of cable is limited to 2 Km in electrified areas

    Effects of Railway Electrification on Telecom circuits

    • 25KV AC traction system causes interference to telecom circuits due to electrostatic and electromagnetic induction
    • Electrostatic coupling (Capacitive coupling): Cable conductors acquire a potential relative to earth due to the catenary’s voltage and distance
    • Electromagnetic coupling (Induction): The current flowing in catenary cables through the rails induces EMFs in parallel conductors
    • Precautions include using a screening factor to reduce induced voltage, implementing guidelines for cable laying, and utilizing isolation transformers to prevent voltage build up
    • Cable laying practices such as laying cables underground, using warning bricks and keeping cables away from the rails are also used to improve safety

    Telecom Quad Cables

    • Underground quad cables are introduced for long-distance communication in electrified areas
    • Various types of 4 and 6 quad cables exist
    • 4 and 6 quad cables use insulated conductors in a quad configuration to reduce interference and have a higher transmission capacity over 25KM lengths of cable

    Cable Laying Practices

    • Cable route surveys, permissions, and identification of soil conditions are essential
    • Cable installation should be at the correct depth below ground or in protective conduits
    • Cable laying practices in areas with major crossings and stations should be conducted carefully to avoid damage
    • Specific guidelines for laying OFC alongside quad cables on various railway routes exist

    Jointing of Underground Telecom Cables

    • Cable lengths are joined using specialized kits
    • Jointing procedures include carefully preparing the cable ends, twisting conductor pairs, soldering, using heat-shrinkable sleeves, and sheath/armour continuity
    • Different types of joints (straight, derivation, straight-cum-derivation) are employed depending on the required circuit type

    Testing of Cables

    • Testing methods of cables before and after installation include tests for continuity, insulation, transmission loss, crosstalk and psophometric noise
    • Proper instruments are needed for each type of tests
    • Each test will have values according to the standards and specification of the equipment in question

    Quad Cable Maintenance

    • Maintenance procedures to prevent cable damage from various sources are essential (ie. lightning, human error, construction work, etc)
    • Essential tools and procedures for cable troubleshooting are described
    • Keeping a Quad Cable Maintenance Register to track and report maintenance activities is critical

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