Wiring Cables and Conductors Note All the mentioned

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 1

Conductors n Copper & Aluminium are commonly used (Table 3. 1) n D. C. & A. C. resistance (skin effect & proximity effect) n A. C. inductance (self inductance for single core cables, plus mutual inductance for multi-core cables) Electrical Installation II 2

Cable Insulation n Polyvinyl Chloride (PVC) – Cheap n 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 3

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

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

Cable Selection & Installation n Fire and explosion – Tradition - MI cables, Modern - FP 400 (fire resistant IEC 331, Low smoke emission BS 6742, Flame retardant IEC 332, etc. ) Electrical Installation II 6

Cable Selection & Installation n 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 7

Cable Selection & Installation n Cable installation methods (refer to Table 3. 11) Revised – e. g. PVC cables in cast-in conduits method 3 n Application of Cables for Fixed Wiring (refer to Table 3. 12) - e. g. PVC non-sheathed cables in conduits, trunkings, etc. Electrical Installation II 8

Cable Rating n 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 < 2 D. Ci - Thermal insulation. Electrical Installation II 9

Cable sizing based on Current Carrying Capacity n 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 10

Cable sizing based on Voltage Drop Consideration n 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. n Additional Thermal Considerations (to be covered later) Electrical Installation II 11

Other Considerations n Size of Cables for General Installations (refer to Table 3. 17) - e. g. 10 A lighting circuits 2. 5 mm 2 1 -C PVC cables n Size of cables supplying large loads - may consider using conductors in parallel Electrical Installation II 12

Busbars n Higher CCC (refer to Table 3. 20) and lower impedance n smaller size compared with the cables of the same CCC n Higher cost than that of cables n Tap-off facilities available n Factory pre-fabricated Electrical Installation II 13

Reduced Neutral Conductors n n 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 14

Identification of Conductors n n Refer to Table 3. 22 New identification colour scheme in alignment with latest BS 7671, HD 3087 S 2 is under consideration. Electrical Installation II 15