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Chapter 3

Wiring Cables and Conductors (Note: All the mentioned tables in this course refer to, unless otherwise specified, Low Voltage Electrical Installation Handbook, by Johnny C.F. Wong, Edition 2004). Chapter 3. Conductors. Copper & Aluminium are commonly used ( Table 3.1 )

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Chapter 3

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  1. Wiring Cables and Conductors(Note: All the mentioned tables in this course refer to, unless otherwise specified, Low Voltage Electrical Installation Handbook, by Johnny C.F. Wong, Edition 2004) Chapter 3 Electrical Installation II

  2. Conductors • Copper & Aluminium are commonly used (Table 3.1) • D.C. & A.C. resistance (skin effect & proximity effect) • A.C. inductance (self inductance for single core cables, plus mutual inductance for multi-core cables) Electrical Installation II

  3. Cable Insulation • Polyvinyl Chloride (PVC) • Cheap • Cross-linked Polyethylene (XLPE) smaller cable size • can be smaller in csa as compared to PVC of same rating • higher continuous temperature rating • higher short-circuit temperature rating • higher current carrying capacity • higher cost • used in public supply cables Electrical Installation II

  4. Cable Selection & Installation • Standards & Statutory Regulations e.g. BASEC, BASEC HAR, etc • Environmental Conditions • Ambient temperature • Weather, moisture, etc. e.g. the ends of mineral-insulated cables shall be suitably sealed. • Mechanical stress Electrical Installation II

  5. Cable Selection & Installation • Environmental Conditions (cont’d) - Solid foreign bodies - Corrosive or polluting substances - Solar radiation & ultra-violet radiation Electrical Installation II

  6. Cable Selection & Installation • Fire and explosion • Tradition - MI cables, Modern - FP400 (fire resistant IEC331, Low smoke emission BS6742, Flame retardant IEC332, etc.) Electrical Installation II

  7. Cable Selection & Installation • Commonly used cables in Hong Kong: • PVC 1-C • PVC/PVC 1-C or M-C • PVC/SWA/PVC • XLPE/SWA/PVC • MI Electrical Installation II

  8. Cable Selection & Installation • Cable installation methods (refer to Table 3.11) Revised • e.g. PVC cables in cast-in conduits  method 3 • Application of Cables for Fixed Wiring (refer to Table 3.12) - e.g. PVC non-sheathed cables  in conduits, trunkings, etc. Electrical Installation II

  9. Cable Rating • Sustained current carrying capacities (standard conditions) • Correction factors: Ca - Ambient temperature Cg- Grouping of cables (>1 no. of multicore or >1 no. of circuits) when clearance between adjacent cables < 2D. Ci - Thermal insulation. Electrical Installation II

  10. Cable sizing based on Current Carrying Capacity • Usually based on the worst case:-where: • It is the standard CCC (Current Carrying Capacity) • In is the rating of the protective device • Need to refer to table for It for different cables. Electrical Installation II

  11. Cable sizing based on Voltage Drop Consideration • Usually based on the simple guideline:- • voltage drop  4% from the origin of the installation. (e.g. service cutout, consumer's main switch) • Need to refer to table for voltage drop for different cables. • Additional Thermal Considerations (to be covered later) Electrical Installation II

  12. Other Considerations • Size of Cables for General Installations (refer to Table 3.17) - e.g. 10A lighting circuits  2.5 mm2 1-C PVC cables • Size of cables supplying large loads - may consider using conductors in parallel Electrical Installation II

  13. Busbars • Higher CCC (refer to Table 3.20) and lower impedance • smaller size compared with the cables of the same CCC • Higher cost than that of cables • Tap-off facilities available • Factory pre-fabricated Electrical Installation II

  14. Reduced Neutral Conductors • High CCC (refer to Table 3.20) • Not generally accepted due to unequal loading or power factor of the phases, harmonic currents in the neutral conductor, 100% neutral preferred. Electrical Installation II

  15. Identification of Conductors • Refer to Table 3.22 • New identification colour scheme in alignment with latest BS7671, HD 3087S2 is under consideration. Electrical Installation II

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