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Questions and Answers
What is one disadvantage of the cable laying method discussed?
Which step is NOT involved in the cable jointing process?
What provides strong mechanical protection in the discussed cable laying method?
Which of the following is a method used to prevent moisture from entering the cable joint?
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What is the current carrying capacity of the cables affected by?
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What is the purpose of providing separators between cables in congested areas?
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Where are cables typically installed when laid on racks inside buildings?
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Which material is NOT mentioned as being used to fix around cable joints?
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What is the purpose of wrapping PVC tape around the areas where the mould will touch the cables?
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What should be checked before adding hardener to the resin?
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How long should the joint be allowed to set before charging the cable?
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What is the melting temperature range for hot pouring compounds used in cable jointing?
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What is a necessary step after mixing the resin and hardener for hot pouring?
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Which of the following is NOT a characteristic of the bituminous compound used for hot pouring?
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In the process of preparing the joint, which step is taken to avoid formation of air bubbles?
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What happens if the mould ends are not enclosed with putty during cable jointing?
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What is the primary consideration when determining the size of racks for cable grouping?
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Which type of joint is used for paper insulated lead sheathed cables up to a voltage grade of 11 KV?
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What protective measures should be taken for cables laid along buildings or structures?
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Which of the following is NOT a requirement for cable joints?
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What temperature should the compounding process reach for proper cable jointing?
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What material is typically used for joints in cables above a voltage grade of 11 KV?
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What is one of the key properties that the material in cable joints should possess?
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Which of the following conditions should be avoided when laying cables?
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Study Notes
Cable Laying Methods
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Laying Under Ground with or without Ducts
- This method is used for long cable routes
- Advantages: Direct and flexible routing
- Disadvantages: Expensive and time-consuming
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Key points to remember:
- Cables should be placed in layers to avoid damage
- The cables should be supported by materials with good mechanical properties
- The cables should be secured to the ducts with appropriate clamps to prevent movement
- The trenches should be backfilled with high-quality soil to avoid future sinking or damage
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Laying in Conduits
- Advantages: Offers protection against mechanical and environmental damage; can be easily identified
- Disadvantages: Expensive; requires careful engineering and can be difficult to move cables if needed
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Key points to remember:
- Conduits should be laid at a depth that is safe from mechanical damage and freezing
- Conduits should be installed in a trench and backfilled with appropriate soil
- Conduits should be properly sealed at both ends to prevent entry of water
- Conduits should be installed in a straight line to avoid stress on cables
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Laying in Channels in the Floor
- Advantages: Suitable for short cable routes in buildings; easier to access; less expensive
- Disadvantages: Can be an eyesore; susceptible to damage by foot traffic
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Key points to remember:
- Channels should be installed in a concrete floor
- Channels should be appropriately sealed to prevent dust and moisture
- Channels should be fitted with covers that are easy to remove
- The cables should be secured to the channels using cable ties
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Laying in Concrete Floors
- Advantages: Ideal for long cable routes; robust installation, less susceptible to damage
- Disadvantages: Difficult to access cables for maintenance or replacement; expensive to install
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Key points to remember:
- The concrete should be of sufficient strength to withstand the weight of the cables
- The cables should be secured to the concrete floor using cable ties to prevent movement
- The cables should be protected with insulating materials to prevent corrosion and short circuits
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Laying in Buried or Underground
- Advantages: The least expensive and most common method
- Disadvantages: Difficult to access for maintenance or replacement; vulnerable to rodent damage
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Key points to remember:
- The cables should be buried at a safe depth to avoid damage from digging
- The cables should be protected from corrosion by wrapping them in insulating materials
- The cables should be laid in a straight line and well-supported to prevent movement
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Laying of Cables in Air (on Racks)
- Advantages: Provides easy access for maintenance or replacement; ideal for high voltage cables
- Disadvantages: Cables can be damaged by mechanical impact; aesthetically less pleasing compared to wall-mounted cables
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Key points to remember:
- The supporting structure should be strong and capable of bearing the weight of the cables
- The cables should be secured to the racks using cable ties
- The cables should be spaced apart to prevent overheating
- The racks should be installed in areas exposed to the least amount of dust and moisture
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Laying Cables along Buildings or Structures
- Advantages: Economical and practical for long, straight cable routes
- Disadvantages: Offers less protection than underground or ceiling-mounted methods; potentially susceptible to damage from wall alterations
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Key points to remember:
- Cables should be secured to the wall using clips or cable ties
- The cables should be routed along the shortest and safest paths
- The cables should be shielded from direct sunlight or heat sources to prevent damage
- The cables should be checked for damage on a regular basis
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Cable Jonting Methods
- Advantages: Helps to reduce the length of cables and minimize material waste
- Disadvantages: Requires specialized skills; must be carefully executed to ensure continuity and prevent faults
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Key points to remember:
- Only use high-quality materials designed for cable jointing
- Perform the steps in the correct order to achieve a strong, reliable connection
- The joint should be protected from water entry by carefully applying sealing compounds
- The joint should be tested after completion to ensure proper electrical conductivity
Types of Cable Faults and Testing Procedures
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Cable Faults
- Ground Fault: This occurs when a cable comes into contact with earth, creating an unexpected path for current
- Short Circuit: This happens when two conductors in the cable come into contact with each other, resulting in a sudden surge of current.
- Open Circuit: This occurs when a cable breaks or has an interruption in its electrical path
- Cable Damage: Causes include mechanical impact, excessive heat, or rodent activity.
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Testing procedures
- Megger Test: This used to measure the insulation resistance of the entire cable system.
- Hi-pot Test: This is used to measure the resistance of the insulation of the cables
- Continuity Test: This checks the electrical continuity of the cable by measuring the resistance or the loop resistance
- Cable Fault Location: By using a specialized instrument, cable faults can be detected and pinpointed along the route.
- Visual Inspection: Regularly check for physical damage, loose connections, or other signs of deterioration.
Requirements of a Good Cable Joint
- The quality of a cable joint should be such that it does not add any resistance to the circuit.
- The materials and techniques used for joining cables should provide adequate mechanical and electrical protection to the joint under all service conditions.
- The joints should be resistant to corrosion and other chemical effects.
Advantages of Pre-fabricated Cable Racks
- Using pre-fabricated racks in factories saves time compared to site fabrication
- Pre-fabricated racks offer better quality and consistency
- They are easier to transport and install
- Pre-fabricated racks provide an economical way to lay out large-scale cabling systems.
Cable Jonting for Various Cable Types
- PVC Cables: Straight through joints using epoxy resin are common for PVC cables
- PILC Cables: Sleeve joints or crimping joints are used up to 11 kV voltages. For higher voltages, compound filled copper or brass sleeves are used in cast iron or fiberglass boxes.
Cable Jonting Compound
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Compounding Process:
- Heat the compound in a special bucket on a fire.
- Stir the compound to ensure even melting
- Check the temperature with a thermometer. Heat to 180°C-190°C.
- Heat the sealing box to 70°C.
Properties of Bituminous Compound
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Bituminous Compound:
- High electrical strength
- Highly resistant to moisture
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Description
Explore various cable laying methods including underground and conduit solutions. Learn about the advantages, disadvantages, and key considerations for each technique. This quiz is essential for understanding the fundamentals of cable installation.
