Electrical Installation II 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

Electrical Installation II 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

Electrical Installation II 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

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

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

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

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

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

Electrical Installation II 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

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

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

Electrical Installation II 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

Electrical Installation II 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

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

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