Electrical Cables and Components Quiz

Cables and Support Systems

• Cables are insulated conductors.
• Cables consist of conductors, insulation, and mechanical protection.
• Components include main, sub-mains, and final sub-circuits.
• Cable support systems: e.g., cable ladders, cable trays, and cable conduits.
• Fire resistance cables: designed for use in fire-prone environments, often using materials like magnesium oxide.
• Busducts: combine conductors, insulation, mechanical protection, and support into a single unit.

Cable Components

• Sheath: Protects the cable from damage.
• Conductor: Usually copper or aluminum, size determined by current rating. Stranded conductors offer flexibility.
• Insulator: Covers the conductor, with higher insulator sizes handling higher voltages.

Cables & Cable Components

• Cables are insulated conductors.
• Three main cable components are Conductor, Insulation, and Mechanical protection.

Conductor

• Conductor size is measured in mm².
• Conductor material is either copper or aluminum.
• Aluminum is lighter and cheaper, but has higher resistivity than copper, leading to a larger size for the same current carrying capacity. Copper is heavier and more expensive, but has lower resistivity.
• Stranded conductors are twisted together for flexibility during installation.
• Total cross-sectional area of individual wires in a stranded conductor is used to determine size.

Conductor/Insulator

• Stranded conductors are comprised of many small wires, enabling flexibility during installation.
• Conductor size is the total cross-sectional area of all wires, excluding air space.
• Insulators are the external coverings of conductors; protecting live conductors from contact.

Other Insulations

• Synthetic rubber insulators handle high temperatures up to 85°C.
• Silicone rubber is used for special applications in temperatures ranging from -60°C to 150°C.
• Magnesium oxide insulation is a fire-resistant insulator.
• MICC cables are fire resistant, able to operate at up to 250°C.

Color Code

• Color coding for electrical wiring standardizes connections in single-phase and three-phase systems.
• Old and new schemes exist.

Single Core and Multi Core

• Single core cables have single conductors, suitable for high-current applications.
• Multi core cables have multiple conductors, suitable for smaller size applications.

Cable Specification

• Specific cables have 3-phase configurations.
• The conductors have a cross-sectional area.
• Insulation is cross-linked polyethylene.
• Sheath is polyvinyl chloride.
• Separate earth cables have a calculated size.

Single & Multi Core Cables

• Conductors are usually stranded copper.
• Insulation is usually cross-linked polyethylene or other polymers.
• Fillers, binders, bedding, armouring, and oversheaths are used as necessary for mechanical protection or specific application needs.

Cable Specification

• Multicore cables are common up to a 120 mm² cross-sectional area.
• Submain cables handle high current loads.
• Final circuits have lower current requirements.
• Circuit protective conductors need their size calculated according to the phase conductors, typically less.

Selection of Cable Size

• Cable size selection is based on current carrying capacity and voltage drop.

Current Carrying Capacity

• Cable size directly affects the current-carrying capacity.
• Higher ambient temperatures reduce current-carrying capacity.
• Enclosures reduce current-carrying capacity.
• Multiple cables together reduce current-carrying capacity.

Selection of Cable Size

• Selecting a cable size requires consideration of ambient temperature, installation factor, grouping factor, and design standards.
• Small cable sizes can lead to overheating, damage, short circuits, and possible fire.
• Large cable sizes are wasteful.
• Standards provide minimum acceptable cable sizes for specific applications (e.g., lighting and power).

Guide from CP5

• Provides detailed information for calculating voltage drop.

What happens if a cable is inadequately sized?

• Inadequate cable sizing can cause conductor overheat.
• This can lead to insulation breakdown, short circuits, or even fires.
• Cable insulation degrades over time due to overheating. This should be avoided.

Voltage Drop

• Equipment voltage range varies with whether it's single or three phase.
• Allowable voltage drop should be considered in calculations.
• Drop should be less than 4% in overall wiring diagrams.

Cable Support

• Cable support systems include cable ladders, cable trays, and cable conduits.
• Use appropriate supports for individual cable types. Different systems cater to various cable sizes.

Installation Details for Socket

• CP5 regulations mandate adequate mechanical protection for wiring within walls, including connections.
• This is essential for safe operation within a building structure.

Cable Support System Installation

• Supports include metal trays or ladders, brackets, and channels.
• These systems are used in a variety of areas including buildings.

Fire Retardant Cables

• Fire retardant cables are designed to continue operating during fires, which is critical.
• Some cables have added fire resistant layers or compounds to give extra protection during a fire.

MICC & Mica-taped FR Cables

• Fire-resistant cables are tested under various conditions to ensure continuous safety, even in extreme situations.
• Materials used for the cables impact the result of these tests.

Functions of Busducts

• Busducts combine multiple functions into one unit. (conductor, insulation, mechanical protection, support)
• Busducts are smaller than cables for larger current requirements, and have lower resistance for high currents than cables.

Busducts

• Busducts combine multiple functions into a single unit.
• Busducts, used at high currents, have low resistance. This helps reduce wiring concerns.
• Busduct usage is common in high rise buildings and factories.

Busducts in Factories

• Horizontal busducts run extensively at high levels in factories.
• Droppers are installed where power is needed.

Cable Tray

• Cable trays are support structures for cables.
• Practical for many wiring needs.

Summary 1

• Summarizes cable components, color coding, cable drawings, current carrying capacity, and sizing criteria.

Summary 2

• Provides a summary of circuit voltage drops, support systems for mounting, and fire-resistant cable types.

Summary 3

• Busduct components, advantages (size, low resistance, ease of installation), and disadvantages (high cost, custom installation) are highlighted.