Electrical Wires and Underground Cables [2023]

In this note, we discuss about the Electrical Wires and Underground Cables. Welcome to Poly Notes Hub, a leading destination for Diploma Engineering Notes Syllabus-wise.

What is Conductors?

Electrical conductors are materials that allow the flow of electric current through them with minimal resistance. They are typically characterized by having a high density of free electrons that can move easily in response to an applied voltage. Common electrical conductors include metals such as copper, aluminum, and silver. These materials are used extensively in electrical wiring, circuits, and various electronic devices to transmit and distribute electrical energy. In contrast, electrical insulators are materials that do not conduct electricity effectively and are used to prevent the flow of electrical current.

Types of electrical wires and underground cables

Here are some notes on various types of conductors used in electrical and wiring applications:

• Wire: Wire is a single, solid conductor typically made of copper or aluminum. It’s commonly used for electrical connections and comes in various gauges or thicknesses, with thinner wire used for low-current applications and thicker wire for higher current needs.
• Cable: A cable is a combination of multiple wires bundled together within a protective sheath. It’s used for transmitting electrical signals or power over longer distances. Common types include electrical cables, data cables, and coaxial cables.
• Bus Bar: A bus bar is a solid, conductive bar or strip, often made of copper or aluminum, used to distribute electrical power within an electrical panel or distribution system. It provides a low-resistance path for current flow.
• Stranded Conductor: Stranded conductors consist of multiple thin wires twisted or braided together. They are more flexible than solid conductors, making them suitable for applications that require flexibility and durability.
• Armored Cable: Armored cable, often referred to as AC cable or BX cable, is a type of electrical cable with a metal armor layer for protection against physical damage and electrical interference. It’s commonly used in industrial and outdoor installations.
• Flexible Cable: Flexible cables are designed to withstand bending and twisting without damage. They are often used in applications where constant movement or flexibility is required, such as in robotics or portable power tools.
• Solid Conductor: A solid conductor is a single, continuous wire with no strands. It is commonly used in applications where stability and minimal signal loss are essential, such as in structured wiring within buildings.
• PVC Wires: PVC (Polyvinyl Chloride) wires have insulation made of PVC material. They are widely used for general-purpose electrical wiring in homes and buildings due to their insulation properties and affordability.
• CTS Wire: CTS (Copper-Clad Steel) wire consists of a steel core coated with a layer of copper. It offers the electrical conductivity of copper while providing greater strength and durability.
• LC Wire: LC (Lead-Covered) wire is used in applications that require protection against chemical and environmental factors. It has a lead sheath to shield the conductor from corrosion and contamination.
• FR Wire: FR ( Fire Retardant ) wires are designed with fire-resistant insulation materials to reduce the risk of fire spread in case of a short circuit. They are commonly used in areas where fire safety is a top concern.

Size of Wire According to BIS

In India, wire sizes are typically specified according to the standards set by the Bureau of Indian Standards (BIS). The wire size is primarily determined by its cross-sectional area, which is specified in square millimeters (mm²). The commonly used wire sizes according to BIS standards include:

1. 1.0 mm²: This size is often used for lighting circuits and smaller loads.
2. 1.5 mm²: Commonly used for general-purpose electrical wiring in homes and small installations.
3. 2.5 mm²: Suitable for higher current-carrying capacity applications, such as power outlets and larger loads.
4. 4.0 mm² and above: Used for heavy-duty applications, industrial installations, and circuits with high current requirements.

Tools used for measurement of wire size

To measure the size of a wire, you can use a few different tools:

1. Wire Gauge (SWG): This is a simple tool that measures the diameter of a wire and can be used to determine its size. It’s based on a standard wire gauge chart.
2. Vernier Calipers: These precision instruments can measure the diameter of a wire accurately. You can then calculate the cross-sectional area using the formula for the area of a circle (πr², where “r” is the radius).
3. Micrometer: A micrometer is a highly accurate tool for measuring wire diameter. It’s suitable for precise measurements.

Different Wire Joining Methods

1. Soldering: This method involves melting solder (a low-melting-point alloy) onto the ends of the wires to join them together. It’s commonly used for small electronic connections and is a permanent joint.
2. Twisting and Wire Nuts: Wires can be twisted together, and then a wire nut (a threaded plastic or metal connector) is screwed onto the twisted wires to secure the joint. This method is used in household wiring for connecting wires within electrical boxes.
3. Crimping: Crimp connectors, also known as crimp terminals, are used to join wires by crimping them onto the conductors using a specialized tool called a crimping tool. It’s often used in automotive and industrial applications.
4. Wire Connectors: Wire connectors, such as Wago connectors, use a spring mechanism to hold wires together. They are easy to install and provide a secure connection. They are commonly used in modern electrical installations.
5. Compression Lugs: These are used for larger wires and cables. They involve crimping or compressing the lug onto the wire end and then securing it to a terminal or stud.
6. Brazing and Welding: In some industrial applications, particularly for heavy-duty or high-temperature environments, brazing or welding can be used to join conductors. These methods provide extremely strong and permanent connections.

Classification of Cable

Based on Voltage Levels:

• Low Tension (LT) Cables:

1. Voltage Range: Typically up to 1 kV (1000 volts).
2. Common Uses: Domestic wiring, small-scale industrial applications, lighting circuits, and appliances.
3. Insulation: Usually insulated with materials like PVC or XLPE.

• High Tension (HT) Cables:

1. Voltage Range: Typically from 1 kV to 33 kV.
2. Common Uses: Medium-sized industrial applications, urban and rural power distribution, and connecting substations.
3. Insulation: Often insulated with XLPE for improved electrical properties.

• Extra High Tension (EHT) Cables:

1. Voltage Range: Exceeding 33 kV.
2. Common Uses: Large-scale power transmission over long distances, interconnecting substations in the electrical grid.
3. Insulation: Usually consists of high-quality materials like XLPE or EPR (Ethylene Propylene Rubber).

Based on Insulation Types:

• Solid Insulated Cables:

1. Insulation Material: Solid materials like PVC, XLPE, or rubber.
2. Advantages: Cost-effective, suitable for indoor and outdoor installations, and easy to handle.
3. Applications: Used in low to medium voltage systems, including building wiring and underground distribution.

• Oil-Filled Cables:

1. Insulation Material: Insulating oil, often mineral oil.
2. Advantages: Excellent dielectric properties, self-healing characteristics, and efficient cooling.
3. Applications: High-voltage applications, including underground and submarine power transmission, and in transformers.

• Gas-Filled Cables:

1. Insulation Material: Gases like sulfur hexafluoride (SF6).
2. Advantages: Superior dielectric strength, compact design, and minimal environmental impact.
3. Applications: High-voltage and extra high-voltage applications, such as in gas-insulated switchgear and transmission lines.

Different Types of Cable Insulation Materials

• Vulcanized Rubber (VIR):

1. Class of Insulation: VIR is a type of organic insulation.
2. Characteristics: It is a natural rubber that has undergone vulcanization, a process that improves its properties like heat resistance and durability.
3. Applications: Historically used in early electrical cables, but it has largely been replaced by newer materials due to limited temperature and environmental resistance.

• Polyvinyl Chloride (PVC):

1. Class of Insulation: PVC is a synthetic or plastic insulation material.
2. Characteristics: PVC is known for its flexibility, ease of handling, and resistance to moisture and chemicals. It’s a common choice for general-purpose electrical wiring.
3. Applications: PVC-insulated cables are used in a wide range of applications, including building wiring, automotive wiring, and low-voltage power distribution.

• Cross-Linked Polyethylene (XLPE):

1. Class of Insulation: XLPE is a thermosetting polymer insulation material.
2. Characteristics: XLPE offers excellent electrical properties, high-temperature resistance, and good resistance to moisture and chemicals. It has replaced many older insulation materials in high-voltage and medium-voltage cables.
3. Applications: XLPE-insulated cables are widely used in medium to high-voltage power distribution, underground and underwater cables, and industrial applications.

• Impregnated Paper:

1. Class of Insulation: Impregnated paper is a type of organic insulation.
2. Characteristics: It consists of layers of paper impregnated with an insulating fluid (such as oil) to enhance its dielectric properties and moisture resistance.
3. Applications: Often used in oil-filled cables and high-voltage power transformers. The impregnated paper provides excellent insulation in these applications.

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