Download Wiring Cables and Conductors

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

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
2
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
3
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
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Cable Selection & Installation

Environmental Conditions (cont’d)
- Solid foreign bodies
- Corrosive or polluting substances
- Solar radiation & ultra-violet radiation
Electrical Installation II
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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
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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
7
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
8
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
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Cable sizing based on Current
Carrying Capacity

Usually based on the worst case:In
It 
C a C g Ci
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
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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
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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
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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
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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
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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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