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)

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

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)

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

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

5
Cable Selection Installation

• Environmental Conditions (contd)
• - Solid foreign bodies
• - Corrosive or polluting substances
• - Solar radiation ultra-violet radiation

6
Cable Selection Installation

• Fire and explosion
• Tradition - MI cables, Modern - FP400 (fire
  resistant IEC331, Low smoke emission BS6742,
  Flame retardant IEC332, etc.)

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

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.

9
Cable Rating

• Sustained current carrying capacities (standard
  conditions)
• Correction factors
• Ca - Ambient temperature
• Cg - Grouping of cables (gt1 no. of multicore
  or gt1 no. of circuits) when clearance between
  adjacent cables lt 2D.
• Ci - Thermal insulation.

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.

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)

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

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

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.

15
Identification of Conductors

• Refer to Table 3.22
• New identification colour scheme in alignment
  with latest BS7671, HD 3087S2 is under
  consideration.