1. 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

2. 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

3. 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

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. 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

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. 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

13. 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

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