Introduction of Electrical Cables
Electrical cables are a type of insulated wires that are used for transmitting electricity or electrical signals from one point to another. These cables are made up of two or more insulated conductors that are twisted or braided together to form a single cable. The conductors are usually made of copper or aluminum, which are good conductors of electricity. The insulation around the conductors is typically made of materials such as PVC, rubber, or cross-linked polyethylene (XLPE), which protect the conductors from moisture, abrasion, and other environmental factors.
General Construction of Cables
The general construction of electrical cables consists of three main components: conductors, insulation, Metallic Sheath, Bedding, Armor and Serving.\\\;\\\;\;\;\;\;\;\;\;
- Conductors: The conductors are the wires that carry the electrical current. They are usually made of copper or aluminum because these metals are excellent conductors of electricity. The size of the conductor depends on the amount of current that needs to be transmitted. The conductors are twisted or braided together to form a single cable. They are usually stranded in order to provide flexibility to the cable
- Insulation: The insulation is a material that surrounds the conductors and prevents them from coming into contact with each other or with other objects. The insulation material can be made of PVC, rubber, or XLPE. The thickness of the insulation depends on the voltage level of the cable and the environmental conditions in which it will be used.
- Metallic Sheath : To protect cables from moisture and harmful liquids ((acids or alkalies) , a metal covering made of lead or aluminium or copper is used over the insulation. This covering helps to cancel out the electric field outside of the cable and also acts as a barrier to prevent humidity from damaging the insulation. It is important that the metal covering is connected to the ground at least once along the cable’s route. If humidity and a strong electric field are present together, it can cause the insulation to deteriorate, which is known as water-treeing and can eventually lead to failure of the insulation.
- Bedding : In order to prevent corrosion and mechanical damage to the metallic sheath, a protective layer called bedding is used. Bedding is typically made of fibrous materials such as jute or hessian tape.
- Armor : Armor is a technique used to further protect electrical cables from mechanical damage, such as impacts, crushing, or cutting. This is achieved by wrapping the cable with a layer of galvanized Steel wires or tapes, which helps to distribute and absorb any external forces that could damage the cable. Armor can also protect the cable from rodents and other animals that may chew on or damage the cable. Armored cables are commonly used in industrial settings or outdoor environments where there is a higher risk of physical damage to the cables.
- Serving : Serving is a technique used to provide additional protection to electrical cables, primarily from mechanical damage and abrasion. It is provided over the armoring. It involves wrapping the cable with a layer of textile material, such as cotton or nylon or jute, in a spiral or braided pattern. Serving helps to distribute the stress and pressure on the cable more evenly, preventing localized damage that could lead to a break in the insulation or conductors. Additionally, serving can provide some degree of protection against moisture and other environmental factors. It is commonly used in situations where cables are subject to frequent movement, such as in robotics or automation applications.
- Outer Sheath: The outer sheath of a cable is the outermost layer that provides protection for the conductors and insulation inside the cable. The main function of the outer sheath is to protect the cable from environmental factors such as moisture, chemicals, abrasion, and UV radiation, and to provide mechanical strength to the cable. The Common materials for outer sheaths include polyvinyl chloride (PVC), polyethylene (PE), cross-linked polyethylene (XLPE), ethylene propylene rubber (EPR), and chlorosulfonated polyethylene (CSPE).
Indian Standards for Electrical Cables
The various Indian Standards for power cables are listed below
- IS 1554 (Part 1) – PVC insulated LV Cables
- IS 1554 (Part 2) – PVC Insulated MV and HV Cables
- IS 7098 (Part 1) – XLPE Insulated LV Cables
- IS 7098 ( Part 2) – XLPE Insulated MV and HV Cables
- IS 694 – light duty PVC Insulated cables up to 1.1KV
International Electrotechnical Commission Standards for Electrical Cables
- IEC 60228: Conductors of insulated cables – This standard specifies the requirements for the construction and dimensions of conductors used in insulated cables.
- IEC 60227: Polyvinyl chloride insulated cables of rated voltages up to and including 450/750V – This standard covers single-core and multicore cables with copper conductors and PVC insulation.
- IEC 60502: Power cables with extruded insulation and their accessories for rated voltages from 1 kV up to 30 kV – This standard covers power cables with extruded insulation for use in electricity transmission and distribution networks.
- IEC 60811: Common test methods for insulating and sheathing materials of electric cables – This standard specifies common test methods for insulating and sheathing materials used in electric cables.
- IEC 61892: Mobile and fixed offshore units – Electrical installations – This standard covers the electrical installation requirements for mobile and fixed offshore units, including cables and their accessories.
Indian Standards for Basic Material and Component of Electrical Cables
The various Indian Standards for basic components and Materials of a Electrical Cable are
- IS 8130 : specification for conductors for insulated electrical cables and flexible cords.
- IS 7098 :IS 7098 has three parts that describe the specifications for crosslinked polyethylene insulated PVC sheathed cables. IS 7098 Part 1 includes specifications for crosslinked polyethylene insulated PVC sheathed cables for working voltages up to and including 1100V. While IS 7098 Part 2 includes specifications for working voltages from 3.3kV up to and including 33 kV. Lastly, IS 7098 Part 3 includes specifications for working voltages from 66 kV up to and including 220 kV.
- IS 3975 : The Indian Standard 3975 provides specifications for low carbon galvanized steel wires, formed wires, and tapes that are intended for use in armouring cables.
- IS 5831 : The Indian Standard 5831 provides specifications for sheath material of cables.
Types of Electrical Cables on the basis of Application
The various types of cables on the basis of application are as Under
- Power cables: These cables are used to transmit electrical power from one point to another. They are typically used in industrial and commercial applications, as well as for power transmission and distribution purposes.
- Control cables: These cables are used to transmit control signals between different devices or systems. They are commonly used in manufacturing plants, machinery, and process control systems.
- Instrumentation cables: These cables are used to transmit low-level electrical signals, such as those generated by sensors or other monitoring devices. They are commonly used in industrial and scientific applications.
- Coaxial cables: These cables are used to transmit high-frequency signals, such as those used for television and radio transmissions. They consist of a central conductor surrounded by a shield that helps to minimize signal interference.
- Ethernet cables: These cables are used to transmit data between devices in a computer network. They are commonly used in offices, homes, and other settings where multiple computers are connected to a single network.
- Fiber optic cables: These cables are used to transmit data using light signals instead of electrical signals. They are commonly used in telecommunications and data transmission applications, as they offer high bandwidth and low signal attenuation.
- Portable cords: These cables are designed for temporary use, such as powering tools or equipment on a construction site. They are flexible and durable, and are often made with materials that are resistant to abrasion, chemicals, and other types of wear and tear.
Types of Electrical Cables on the basis of Voltage Level
The various types of cable on the basis of voltage Level are as under
- Low voltage cables: These cables are designed to carry voltages up to 1000 volts. They are commonly used for lighting, power distribution, and other low voltage applications.
- Medium voltage cables: These cables are designed to carry voltages between 1000 and 35,000 volts. They are commonly used for power distribution in industrial and commercial applications.
- High voltage cables: These cables are designed to carry voltages between 35,000 and 230,000 volts. They are commonly used for power transmission over long distances, such as from power plants to substations.
- Extra high voltage cables: These cables are designed to carry voltages above 230,000 volts. They are used for long distance power transmission and distribution, such as between different regions or countries.
- Ultra-high voltage cables: These cables are designed to carry voltages above 800,000 volts. They are used for extremely long distance power transmission, such as across continents.
Types of Domestic Wires ( Household Wires) on The basis of Resistance to Fire
Domestic wires, also known as household wiring cables, are typically categorized based on their resistance to fire. Here are some of the most common types of domestic wire on the basis of their resistance to fire:
- Non-flame retardant (NFR) wires: These wires are not designed to resist fire and are made of PVC material. They are the most basic and economical type of wire used in domestic electrical installations.
- Flame retardant (FR) wires: These wires are designed to resist fire and are made of PVC material with added flame-retardant chemicals. They are commonly used in domestic electrical installations where there is a risk of fire.
- Low smoke and fume (LSF) wires: These wires are designed to emit low levels of smoke and fumes in case of a fire. They are commonly used in enclosed spaces where smoke and fumes can pose a hazard, such as in high-rise buildings and public transportation systems.
- Zero halogen (ZH) wires: These wires are designed to emit low levels of toxic gases and fumes in case of a fire. They are commonly used in areas with high population density, such as hospitals, schools, and residential buildings.
- Fire resistant (FR) wires: These wires are designed to resist fire and maintain their functionality even in high temperatures. They are commonly used in critical areas, such as emergency lighting, fire alarms, and sprinkler systems.
- Flame retardant low smoke (FRLS) Wires : FRLS wires, also known as Fire Retardant Low Smoke wires, are a type of electrical cable that is designed to have enhanced fire-resistant properties. They are commonly used in buildings and other structures where fire safety is a major concern, such as schools, hospitals, and public transportation systems.
- Flame Retardant High Resistance (FRHR) Wires : FR HR wires stand for Fire Retardant High Resistance wires, which are a type of electrical cable that has enhanced fire-resistant properties and can withstand high temperatures. FR HR wires are designed to be used in high-risk applications where the cable is likely to be exposed to high temperatures and/or flames, such as in industrial plants, furnaces, and boilers. They are made with a special insulation material that is designed to withstand high temperatures and provide enhanced fire resistance.
Classification of Conductors in Electrical Cables and Wires as Per IS 8130
IS 8130 is the Indian Standard that specifies the requirements for conductors for insulated electric cables and wires. As per this standard, conductors are classified into five classes based on their construction and materials used. These classes are:
- Class 1: This class consists of solid conductors made of copper or aluminum. It can be upto 16 sqmm or as specification of project requirement.\\\;\\\;\;\;\;\;
- Class 2: This class consists of stranded conductors made of copper or aluminum. The strands can be either round or sector-shaped.\\\;\\\;\;\;\;\;
- Class 3: This class consists of conductors made of copper wires that are either braided or wrapped around a core.
- Class 4: This class consists of conductors made of aluminum wires that are either braided or wrapped around a core.
- Class 5: This class consists of flexible conductors made of copper or aluminum. The conductors can be either stranded or composed of multiple layers of twisted wires.\\\;\\\;\;\;\;\;
- Class 6: Extra flexible conductors are a type of electrical wire mainly made of copper. They are designed to be more flexible than standard wire. They are commonly used in applications where the wire will be subject to constant movement or vibration, such as in robotics, automation, or medical equipment.\\\;\\\;\;\;\;\;
Difference Between PVC Insulation and XLPE Insulation
PVC (Polyvinyl Chloride) and XLPE (Cross-linked Polyethylene) are two common types of insulation used for electrical cables. While both materials provide insulation and protection to the wire, there are some key differences between PVC and XLPE insulation.
- Material Properties: PVC is a thermoplastic material, which means it can be easily melted and reformed. XLPE, on the other hand, is a thermoset material, which means that once it is formed, it cannot be remelted or reformed. This makes XLPE more durable and resistant to heat and chemical damage.
- Temperature Resistance: XLPE has a higher temperature resistance than PVC, making it suitable for use in high-temperature applications. XLPE insulation can withstand temperatures up to 90°C, while PVC insulation is limited to 70°C.
- Electrical Properties: XLPE has a lower dielectric constant than PVC, which means it is better at insulating and has a higher breakdown voltage. This makes it more suitable for high-voltage applications.
- Environmental Considerations: PVC insulation contains halogens, which can release toxic gases when burned. XLPE insulation, on the other hand, is halogen-free and does not release toxic gases when burned. This makes XLPE a more environmentally friendly option.
Abbreviations of PVC and XLPE Cables OR Cable Codes
A = Aluminium Conductor
Y = PVC Insulation or PVC Sheath
2X = Cross Linked Polythene Insulation
W = Round Steel Wire Armoring
WW = Double Round Steel Wire Armoring
F = Flat (Strip) Steel Wire Armoring
C = Metallic Screen Usually of Copper
CE = Metallic Screen Usually of Copper over each individual core
Wa = Aluminium Round Wire
Fa = Aluminium Flat (strip) steel Wire armoring