Class 11 Power Chapter 5 Repairing of Cable Joints

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Class 11 Power Chapter 5 Repairing of Cable Joints

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Repairing of Cable Joints

Chapter: 5

SESSION 1: ELECTRICAL CABLE JOINTING METHODS

Check Your Progress

A. Write short notes on:

1. LT cables Joints.

Ans: LT cable joints connect, extend, or repair low-voltage cables (1.1 kV class). They maintain electrical continuity, insulation, and protection. 

Types include:

(i) Straight-through joints.

(ii) T/branch joints.

(iii) Transition joints.

(iv)  End terminations.

Jointing involves:

(i) Crimping conductors.

(ii) Rebuilding insulation.

(iii) Bonding/earthing screens and armor.

(iv) Sealing for moisture protection.

Good practice includes:

(i) Proper preparation.

(ii) Correct crimping.

(iii) Testing before energizing.

This ensures reliable and safe electrical connections.

2. Straight through joint.

Ans: Straight through Joints are an important part of today’s power cable networks. These joints offer reliability and flexibility to meet the demands of cable networks.

Straight through Joints provide:

(i) Quick cable preparation.

(ii) High electrical insulation. 

(iii) No moisture ingress.

(iv) Good mechanical strength 

(v) Compact dimensions and is suitable for all conductor, shape and material.

Straight through Joints are made by metal joining processes, such as welding and soldering.

3. Britannia Joint.

Ans: This type of joint is made only on solid conductors and cannot be made on stranded conductors. Two conductors to be joined are brought in front of each other of about 6 inch (150 mm) of length. Both the conductors should be clean. If the conductor is of copper; it should make a good electrical connection. Then ends of both conductors are bent through half centimetre and placed on each other. The length of contact portion should be min. 100 mm. This joint should be bound by 14 mm copper wire. 

4. T-joint.

Ans: These types of joints are used for branching of a service cable from a main cable. T-joints are helpful as turning and twisting of cable damages its outer core.

B. State whether the following statements are True or False:

1. Western Union joint are used for all conductors. 

Ans: False.

2. Married joints should not be made between aluminium conductors. 

Ans: True.

3. Crimping is necessary for joining the cable.

Ans: True.

C. Short answer questions:

1. List the steps used in preparing of the cable.

Ans: Preparing the cable before jointing includes the following steps:

(i) Remove the over sheath and the wire armour.

(ii) Separate the wire armour and bend the wires away from the cable; place the support ring under the armour at each side of the joint.

(iii) Cut back the cable insulation.

(iv) Remove the insulation from each of the conductors.

2. Explain the different types of joints.

Ans: The different types of joints are as under:

(i) Straight through Joint: Straight through Joints are an important part of today’s power cable networks. These joints offer reliability and flexibility to meet the demands of cable networks.

Straight through Joints provide:

Quick cable preparation.

High electrical insulation. 

No moisture ingress.

Good mechanical strength 

Compact dimensions and is suitable for all conductor, shape and material.

Straight through Joints are made by metal joining processes, such as welding and soldering.

(ii) T-Joint: These types of joints are used for branching of a service cable from a main cable. T-joints are helpful as turning and twisting of cable damages its outer core.

(iii) Terminal Joint: These type of joints connect cable to switch gear, transformer terminal or to an overhead line.

(iv) Conductor Joint: The length of distribution lines are in kilometers and one coil of conductor is unable to solve the length problem. Hence, jointing the conductor is necessary. 

(v) Britannia Joint: This type of joint is made only on solid conductors and cannot be made on stranded conductors. Two conductors to be joined are brought in front of each other of about 6 inch (150 mm) of length. Both the conductors should be clean. If the conductor is of copper; it should make a good electrical connection. Then ends of both conductors are bent through half centimetre and placed on each other. The length of contact portion should be min. 100 mm. This joint should be bound by 14 mm copper wire.

(vi) Telephone Joint (Western Union): This joint is used only for solid conductors. It is used for conductors of size 8 SWG or higher size. First, bend is given at 100 to 125 mm from the edge and are placed over each other. Then each one is twisted with another conductor.  

(vii) Married Joints: This joint is made between copper conductors having a central strand of GI wire. It should not be made between aluminium (Al) conductors. Approximately 175 to 200 mm length conductor strands are unwound. The GI strand of both conductors should be broken up to 175 mm in length. Both conductors should be brought in front of each other and their strands should be woven in each other. The strand of one conductor is twisted on other conductor, and the strand of the other conductor is twisted on the first. Likewise all the strands twisted and then soldered. This is used only for small span length.

(viii) Sleeve Joint: It can be made with any type of aluminium conductor. Graphite Greece is applied over the conductor and sleeves should be taken. These sleeves should be placed on the conductor. Sleeves should be twisted by twisting the wrench. This joint is made for LT, HT, ACSR, AAC conductors up to 0.06 cm2.

(ix) Compression Joint: This joint is used for conductors of more than 0.06 cm2 sizes. For jointing, two different sleeves are used. Steel sleeve is used for steel conductor strands and aluminium. sleeve is used for Al. conductor strands. There are two holes in Al. sleeve. Rebating is done through these holes. 

3. Differentiate between fixture joint and western union splice joint.

Ans: The differences between fixture joint and western union splice joint are as under:

Western Union splice joint	Fixture joint
To increase the length of a cable a straight joint is used for small solid cables.	This is a type of branch joint connecting a thin wire (branch line) to the thick wire (main line), such as those used in lighting fixtures.
Remove the insulation of cable.	Remove the insulation of wire.
Bring the two conductors to a crossed position and then make a long bend or twist in each wire.	Wrap the fixture wire around the branch wire.
Wrap the end of one of the wires around the straight portion of the other wire, and then do the same for the other wire. Repeat this for about four or five times.	Bend the branch wire over the completed turns.
Press ends of the wires down close to the straight portions of the wire to prevent the ends from piercing through the insulation tape.”	Wrap the remaining fixture wire over the bent branch wire.
Insulate the joint using the insulation tape.	5) “This can be followed by soldering and taping, or simply taping of the joint.

4. Explain the procedure for heat shrinking straight through joint.

Ans: In a heat shrink direct joint, both ends of the cable are prepared according to the kit’s cut-backs, and the conductors are crimped into the appropriate ferrules. The stress-control/insulation tube and finally the adhesive-lined outer sleeve are heated and reconditioned from the center toward the ends to eliminate air gaps and ensure a firm seal. The armor/screen is continuity bonded and connected to earth, allowing the joint to cool. Finally, an IR/continuity (and VLF/Hi-pot at MV) test is performed, and the joint is marked/recorded.