Schedule

1
Schedule
2
Introduction
Load Estimation
Terminology
Basic Equipment
Codes and Standards
Power Distribution Final Circuit
Standby Generator and Power Supplies
Protection Cable Wiring
Earthing
Design of Electricity Distribution
3
Power Distribution Final Circuit

• Date 6 Nov 2008

4
Question

• What kind of factors affecting the choice of
  wiring system?

5
Power Distribution and Wiring System - 1

• Installation Cost
• Purpose and planned duration of the installation
• Environment factors and installation conditions
• Type of building construction
• Flexibility of the system and circuit arrangement
• Appearance of the finished installation
• Safety aspect
• Nature of power supply and type of earthing
  system

6
Installation at High Humidity Environment - 2

• The wiring system should be selected and erected
  so that no damage is caused by high humidity or
  ingress of water during installation, use and
  maintenance.
• All joint should be suitably insulated and
  protected against the effects of moisture or
  water. Copperclad aluminum conductors should not
  be used.
• Every entry to finished ducts or trunking should
  be placed so as to prevent the ingress of water
  or be protected against such ingress. Where water
  may collect or condensation may form in a wiring
  system, provisions should be made to drain it
  away.

7
Installation at Adverse Ambient Temperature - 1

• The wiring system including cables and wiring
  accessories, should be suitable for the highest
  and lowest ambient temperature that likely to
  encountered.
• The electrical insulation shall withstand the
  maximum permissible operating temperature of the
  class of insulation to BS 2757.

8
Installation at Adverse Ambient Temperature - 2

• For general-purpose PVC cable, the maximum
  permissible conductor of operating temperature is
  70oC and the maximum permissible ambient
  temperature is 65oC.
• In every vertical trunking or duct wiring
  installations, suitable internal barriers sould
  be provided between floors or at intervals of 5m
  whichever is the less.

9
Installation at Adverse Ambient Temperature - 3

• Suitable measures shall be provided to avoid the
  effects of heat from external source including
  solar gain such as shielding or placing
  sufficiently far from the source of heat or
  selecting insulation suitable for those
  temperature.

10
Index of Protection

• The code that specifies the protection of
  encloses that can be used within certain
  environment. The first numeral indicate the
  protection against ingress of solid bodies. The
  second number indicate the protection against the
  ingress of liquids.

IP XX
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Index of Protection

• General Use
• Indoor Use IP2X
• Outdoor Use IP54 (Weather-proof)

15
Application of Wiring System
16
Typical Schematic Wiring Diagram for Internal
Power Distribution System
17
General Requirement of Internal Power
Distribution System

• a) Basic Requirements
• b) High Voltage Distribution
• c) Mains
• d) Sub - Main
• e) Lateral Main
• f) Installation Methods of Cables

18
General Requirement of Internal Power
Distribution System

• a) Basic Requirements 1
• Every installation shall be divided into circuits
  as necessary to avoid danger in the event of a
  fault, and to facilitate safe operation,
  inspection, testing and maintenance. Each circuit
  should be separately protected by an overcurrent
  protective device. Separate circuits shall be
  provided for parts of the installation which need
  to be separately controlled in such a way that
  these circuits are not affected by failure of
  other circuits.

19
General Requirement of Internal Power
Distribution System

• a) Basic Requirements 2
• Protective devices of each circuit should be
  clearly labelled or identified so that the rating
  of the devices and circuits they protect can be
  easily recognized.

20
General Requirement of Internal Power
Distribution System

• B) High Voltage Distribution-1
• Although residential and the majority of
  commercial installations are adequately served
  from LV-intake or HV-intake-LV distribution,
  there are many industrial and some large
  commercial development projects require HV intake
  with extensive HV distribution system through the
  sites or buildings.
• For example, a hospital or an university with a
  large campus, a cross harbor tunnel with
  high-tension motors for ventilation fans, a very
  large commercial block and a large factory with
  several electrode boilers.
• For these, the power company provides the main
  supply point through its own switchgear complete
  with bulk metering, and the customer is then
  responsible for the installation of suitable high
  voltage switchgear, all cabling and the required
  number of on-site substations.

21
General Requirement of Internal Power
Distribution System

• B) HV Ring Main Distribution system
• Just similar to the ring main system which used
  by power company in their 11kV network

22
General Requirement of Internal Power
Distribution System
Standard method of ring main connection mixed
with radial feeding
23
General Requirement of Internal Power
Distribution System

• B) Advantage of HV Ring Main Distribution system
• Even in the event of a cable fault on the ring,
  it is still possible to maintain or restore
  supply to all points by opening the switches on
  both sides of the fault.
• Additional outlets to the ring may be easily
  installed without shut downs.
• Greater maintenance facilities are available both
  on the ring feeder circuit breakers and the RMUs.
• In additional, if the main HV switchboard is
  sectionalized and fed from more than one
  suppliers substations, a ring main may be
  supplied from two different sections, thus
  improving security.
• Apart from fault conditions, it is also possible
  to operate a ring main in open mode as the
  preferred arrangement but, for whatever purpose
  it must be ensured that neither of the section is
  overload.

24
General Requirement of Internal Power
Distribution System

• c) Mains - 1
• Consumer main switch shall be installed and
  connected immediately before the supply co.s
  meter.
• A common main switch shall be installed to
  control all the communal installation of the same
  consumer.
• The consumer main switch should incorporate
• Means of isolation and switching
• Means of protection against overcurrent, and
• Means of protection against earth leakage.

25
General Requirement of Internal Power
Distribution System

• c) Mains - 2
• The main switch or circuit breaker shall have a
  short-circuit breaking capacity of 40kA at low
  voltage.
• The characteristic of the main switch shall
  disconnect within 5 seconds during an earth
  fault.
• The switchboard shall incorporate Castell key
  interlock or other means to prevent the supply
  transformers operated in parallel. All
  interconnecting devices including the bus-section
  switch shall be of 4-pole type with electrical
  and mechanical interlock.

26
General Requirement of Internal Power
Distribution System

• c) Mains - 3
• Where standby generator is installed,
  mechanically interlocked 4-pole changeover device
  shall be used for interconnection between the
  normal and standby source. A local switch shall
  be installed after a changeover device.
• Single phase consumer main switch shall be of
  double pole type.
• A schematic wiring diagram showing the main
  distribution system should be displayed near the
  main switch with rating 100A or above.

27
General Requirement of Internal Power
Distribution System

• c) Mains - 4
• Each consumer installation shall provided his own
  earthing system
• For 3 phase installation with main switch rating
  of 160A and above, C.T. operated meter shall be
  installed.
• Warning Notice DANGER-ELECTRICITY, UNAUTHORISED
  ENTRY PROHIBITED with Chinese translation shall
  be painted or engraved on plastic boards
  permanently fixed outside the door of
  switchrooms. Each character shall not less than
  50mm high.

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General Requirement of Internal Power
Distribution System

• c) Mains - 5
• The mina earthing terminal of the installation
  should be bonded by a conductor of not less than
  150mm2 copper to the electricity suppliers
  transformer earth or metallic sheaths of service
  cable.

29
General Requirement of Internal Power
Distribution System

• c) LV Distribution-1
• LV distribution exist in nearly all electrical
  installations.
• Nearly all LV distribution are in radial from.
• The greater the impedance of the cable from the
  secondary of the transformer to the LV
  switchboard, the less be the potential
  short-circuit current, and therefore these cables
  should not be larger than necessary.
• If two 1500kVA transformer were connected in
  parallel, then the potential fault current could
  be as much as 60MVA. As this exceeds the breaking
  capacity of most standard LV switchboards ( which
  is usually only 31 MVA, it would entail the
  installation of much more expensive switchboard
  or special high-reactance transformers, or split
  the LV main switchboards into two or more
  separate sections, each section being fed from a
  transformer not exceeding 1500kVA.

30
General Requirement of Internal Power
Distribution System

• c) LV Distribution-2
• The greater the impedance of the cable from the
  secondary of the transformer to the LV
  switchboard, the less be the potential
  short-circuit current, and therefore these cables
  should not be larger than necessary.
• If two 1500kVA transformer were connected in
  parallel, then the potential fault current could
  be as much as 60MVA. As this exceeds the breaking
  capacity of most standard LV switchboards ( which
  is usually only 31 MVA, it would entail the
  installation of much more expensive switchboard
  or special high-reactance transformers, or split
  the LV main switchboards into two or more
  separate sections, each section being fed from a
  transformer not exceeding 1500kVA.

31
General Requirement of Internal Power
Distribution System

• c) LV Distribution-3
• If sectionised is used in switchboard interlocked
  bus-section switches should be provided

32
Typical ring main feeding six distribution boards
33
Radial distribution diagram for typical small
commercial building meters on each floor if
required
34
General Requirement of Internal Power
Distribution System

• C) Rising Mains-1
• 1) Cable, including prefabricated tee-off cable.
• The selection of cable as rising mains is usually
  limited by its current carrying capacity (CCC)
• The cable may be single-core insulted cable, or
  multi-core armoured cable.
• For single-core, p.v.c.-insulated. Non-armoured
  cable, the largest cross sectional area is
  1000mm2 giving a CCC of 1200A.
• As a rule of thumb, when the demand exceeds 800A,
  busduct is preferred.

35
General Requirement of Internal Power
Distribution System

• c) Rising Mains-2
• 2) Insulated busduct (or busbar) system,
  including feeder type and plug-in type busduct.
• The rating of busduct could be up to 5000A or
  even higher. The provision of plug-in unit
  provide flexibility for tee-off at any location/
  floor at anytime when demand required.
• The bus may be insulated conductor or bare
  conductors totally enclosed in continuous steel
  trunking.

36
General Requirement of Internal Power
Distribution System

• c) Rising Mains-3
• The following factors affect the selection of the
  type of rising main
• Load assessment
• Load distribution
• Environmental conditions such as ambient
  temperature and humidity
• Heights of riser
• Maximum allowable voltage drop
• Fault level
• Likelihood of alternation and future extension/
  expansion being frequently required
• form, types and usage of the building
• whether the wiring is to be installed during the
  construction of a building, in a completed
  building, or as and extension system.
• Capital outlay required
• Planned duration of installation

37
General Requirement of Internal Power
Distribution System

• d) Sub-main - 1
• Any building of more than four floors including
  the ground floor and designed for occupation of
  more than one consumer shall be provided with 3
  phase electrical rising mains with 3 phase and
  neutral tee-off at each floor
• Type of rising mains could be one of the
  followings
• Insulated conductors in trunking/ conduit
• Armoured cables suitably supported
• Bare conductors in trunking

38
General Requirement of Internal Power
Distribution System

• d) Sub-main - 2
• Each riding mains installation shall be protected
  against overcurrent and earth leakage and shall
  be equipped with suitable means of isolation.
• For busbar installation having a rated capacity
  not exceeding 400A in each phase of a 3 phase 4
  wire system, the associated neutral busbar should
  have a cross-sectional area not less than the
  cross-sectional area of the phase busbar.

39
General Requirement of Internal Power
Distribution System

• d) Sub-main - 3
• Riser earthing conductor for multi-tenant
  installations shall be installed and the minimum
  size of riser earthing conductor is 70mm2 copper.
• The loadings on 3 phase rising mains should be
  properly balanced. The neutral conductor should
  have a suitable current carrying capacity to
  cater for any imbalance or harmonic current.

40
General Requirement of Internal Power
Distribution System

• d) Sub-main - 4
• The design of rising mains installation should be
  agreed by the electricity supplier.
• No part of the communal installation should pass
  through any individual consumers unit within the
  multi-consumer building.
• No cable, other than that for lift installation
  governed by BS5655, shall be run in lift shaft.

41
General Requirement of Internal Power
Distribution System

• e) Lateral Mains - 1
• Adequate space for lateral mains and meter board
  wiring shall be provided in meter room.
• The loading on 3 phase lateral mains should be
  balanced as far as practicable.
• An installation requiring more than 60A is
  required to be arranged to service a 3-phase
  supply.
• Appropriate correction factors shall be applied
  for determining the current carrying capacity of
  cables.

42
General Requirement of Internal Power
Distribution System

• e) Lateral Mains - 2
• Distribution board, switchgear and busbar chamber
  should have phase identification.
• Where cables, conducts, ducts pass through
  structural element such as floors and walls, the
  openings shall be sealed by appropriate fire
  resistant materials. In addition, internal
  fire-resistant barriers shall be provided to
  prevent the spread of fire.
• Segregation of low-voltage circuits, fire alarm
  circuits and telephone/ telecommunication
  circuits shall be made when they run together.

43
General Requirement of Internal Power
Distribution System

• e) Lateral Mains - 3
• Connection between the electricity suppliers
  meter and the consumers main switch should be
  not less than 4mm2 stranded copper conductor.
• The insulation and/ or sheath of the cables shall
  be removed for a distance of 150mm from the
  connection, and replaced if necessary by suitable
  heat-resisting insulation when connecting the
  cable to bare conductors/ busbar.

44
General Requirement of Internal Power
Distribution System

• e) Lateral Mains - 4
• Warning notice DANGER in red legible letter
  with Chinese translation shall be displayed near
  each distribution board, Each character shall not
  less than 10mm high.
• Where an installation is connected to rising
  mains, agreement should be obtained from the
  owner of rising mains if new current demand
  exceed that before. Moreover, prior approval from
  the power company should be obtained before any
  alteration work is carried out.

45
General Requirement of Internal Power
Distribution System

• f) Installation methods of cables
• According to he CP for WP or IEE Wiring
  Regulations, cables can be in the following ways
• Open or clipped direct
• Embedded direct in building ,materials
• In conduit
• In trucking
• In free air, on cleats, brackets or ladder
• In building voids
• In trenched

46
General Requirement of Internal Power
Distribution System

• What is a final circuit?

47
General Requirement of Internal Power
Distribution System

• Definition of Final Circuit
• A circuit connected directly to current using
  equipment, or to a socket outlet or other outlet
  points for the connection of such equipment.

48
General Requirement of Internal Power
Distribution System

• Final Circuit Typical Arrangement 1
• IEE Reg. 314-01-04 states that an installation
  comprises more than one final circuit, each shall
  be connected to a separate way in a distribution
  board and that the wiring to each final circuit
  shall be electrically separate from each other.

49
General Requirement of Internal Power
Distribution System

• Final Circuit Typical Arrangement 2
• Typical Arrangement shall be
• Two lighting circuits to ensure the whole unit
  will not be in darkness if a fault occurs on one
  lighting circuit.
• Circuit for 5A or 15A socket outlet to be fed by
  an exclusive radial final circuit. The maximum
  loading of each socket outlet shall be 5A or 15A
  respectively.

50
General Requirement of Internal Power
Distribution System

• Final Circuit Typical Arrangement 3
• Circuit for 13A socket outlets complying with
  BS1363.
• Separate circuit for each large current-using
  appliance such as room cooler, cookre or kitchen
  appliance.
• Lighting circuits should be electrically separate
  from power circuits except that it may be
  connected to bell transformers or electric
  clocks.

51
Conduit Wiring SystemType of Conduit

• Steel Conduit to BS 4568 Part 1
• A) Light duty type plain and conduits
• Limited to use in dry situation
• Unsuitable for bending
• Low degree of mechanical protection
• B) Heavy duty type screwed-end conduits
• Back enamel for internal use in dry situation
• Hot-dip galvanized for external use in situation
  subject to dampness or water condensation
• Good mechanical strength and electrical
  continuity.

52
Conduit Wiring SystemType of Conduit

• Steel Conduit to BS 4568 Part 1
• C) Classification for protection

53
Conduit Wiring SystemType of Conduit

• Steel Conduit to BS 4568 Part 1
• D) Heavy duty hot-dip galvanized steel conduit
  system is the most common use system for surface
  conduit wiring and concealed conduit wiring.
  Conduit is supplied in standard lengths of 4
  meters and is manufactured in accordance with
  BS4568.

54
Conduit Wiring SystemType of Conduit

• Plastic conduits
• To BS4607 Part 1 and 2
• Characteristics light, easily bend, less
  installation time, no water condensation, lower
  cost
• Heavy duty PVC conduits can be concealed but CPC
  are required.

55
Conduit Wiring SystemType of Conduit

• Copper Conduits
• High resistance to corrosion
• Last for long time
• Higher cost
• Act as excellent circuit protective conductor
  (CPC)

56
Conduit Wiring SystemType of Conduit

• Aluminum Conduits
• Light weight and lower cost
• Not so good in mechanical protection
• Flexible Conduits
• To BS731 Part 1
• Used for final connection to machinery
• CPC are required.

57
Conduit Wiring SystemSizing of Conduit - 1

• EMSDs COP for the Electricity (Wiring)
  Regulations provides the following tables for
  ease of conduit sizing
• Table A, B for 1/C PVC cables in a straight run
  3m
• Table C, D for 1/C PVC cable in conduit run gt 3m.
• The conduit size is considered satisfactory if
  the conduit factor is equal to or exceeds the sum
  of the cable factors

58
Conduit Wiring SystemSizing of Conduit - 2
Table A Cable factors for short straight runs
59
Conduit Wiring SystemSizing of Conduit - 3
Table B Conduit factors for short straight runs
60
Conduit Wiring SystemSizing of Conduit - 4
Table C Cable factors for long straight runs,
or runs incorporating bends
61
Conduit Wiring SystemSizing of Conduit - 5
Refer to Table A and B
Table D Conduit factors for runs incorporating
bends
62
Conduit Wiring SystemSizing of Conduit - 6

• Example
• In a conduit installation the length of run is
  10m, assuming 2 right-angle bend. What is the
  conduit size to enclose four 2.5 mm2 PVC cables?
• From Table C, factor for one 2.5mm2 cable 30
• Therefore, four 2.5mm2 cables 4 x 30 120
• From Table D, suitable conduit size with a factor
  of 141(gt120) is 20mm.
• 10m Vs 2 bends, cable factor 141

63
Trunking Wiring System - 1

• Use in conditions where a considerable no. of
  cables are required in an installation or where
  cables are too large for drawing into conduits.
• Erection time is reduced (wiring is easier and
  quicker)
• Multi-compartment trunking provides circuit
  segregation.

64
Trunking Wiring System - 2

• Typical types of trunking
• A) Steel trunking for busbar rising mains.
• B) PVC skirting 3-compartment trunking for
  fitting-out wiring works where different category
  circuits such as Telephone cable, CABDS cable
  power supply cable are to be installed in same
  run.
• C) Floor trunking to BS 4678 Part 2 provides
  cabling to service boxes flushed with floor level
  (e.g. in open-plan office or dental room)
• D) Tap-on trunking in factory for internal power
  supply to machinery by plugging into the overhead
  trunking.
• E) Steel surface trunking for cable to BS 4678
  Part 1

65
Trunking Wiring System - 3

• Classification for protection against corrosion

66
Sizing of Trunking - 1
Table E Cable factors for trunking
67
Sizing of Trunking - 2
Table F Factors for trunking
68
Sizing of Trunking - 3

• Example
• What is the maximum no. of 10mm2 PVC cables
  permitted in 50mm x 50mm trunking?
• From Table E, factor of 10mm2 conductor 36.3
• From Table F, factor of 50 x 50mm trunking 1037
• Maximum no. of cable 1037 36.3
• 28.56 (say 28)

69
Ducting - 1

• It provided mechanical protection for cable run
  in the ground or under concreted floor.
• Types of ducting
• Concrete ducts
• Steel underfloor ducts
• Fibre underfloor ducts
• Maximum spacing factor is 35.
• It should be securely fixed and protected against
  corrosion and mechanical damage.

70
Ducting - 2

• Entries to duct must be protected against the
  inflow of water.
• Cables installed in underground ducts shall have
  a metal sheath.
• Underfloor trunking should be fabricated with
  sheet steel of not less than 12mm thickness for
  compartment width up to 100mm, but at least 1.6mm
  thickness for compartment width over 100mm. The
  minimum thickness of 1mm shall be used for the
  partitions and connector material.

71
Segregation of Circuits - 1

• 1) Suitable segregation between enclosed circuits
  with different categories shall be provided in
  wiring. For example, a low voltage circuit shall
  be separated from an extra-low voltage circuit.
• 2) Types of Circuit

72
Segregation of Circuits - 2

• 3) Low Voltage circuit shall be segregated form
  extra-low voltage circuit. Extra-low voltage
  cables shall not be drawn into the same conduit
  or duct, or terminated in the same box or block
  as low voltage cables unless the former are
  insulated for the highest voltage present in the
  low voltage circuit.
• 4) Cables of fire alarm and emergency lighting
  circuits shall not in any circumstances be drawn
  into the same conduit duct or ducting of other
  cables.

73
Segregation of Circuits - 3

• 5) Electrical services shall not be installed
  with pipes or tubes of non-electrical services
  (e.g. air, gas, oil, or water) in the same
  conduit, ducting or trunking. This requirement
  does not apply where the various services are
  under common supervision and it is confirmed that
  no mutual detrimental influence can occur.
• 6) For cables of category 1,2,3 circuits that are
  installed without enclosure or underground, a
  minimum separation of 50mm should be provided
  between different category circuits or
  alternatively at least 25mm separation with slabs
  of concrete inserted between the circuits and the
  shortest path round the concrete should exceed
  75mm.

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Segregation of Circuits - 4

• 7) Insulated bridge of at least 6mm thick should
  be used for separation of surface wiring of
  Category 1,2,3 circuit running across each other.
  The bridge should overlap the cables by at least
  25mm on either side of point of crossing.
• 8) For cables of Category 4 circuit that are
  installed without enclosure or underground, a
  minimum separation of 300mm should be provided
  between Categories or alternatively a reduced
  separation with 50mm thick slabs of concrete
  inserted between the circuits and the shortest
  path round the concrete should exceed 180mm.

75
Standard Circuit for 13A Socket Outlet

• The development of the BS1363 plug and socket
  system and the associated concept of ring circuit
  have made possible the provision of large numbers
  of socket outlets at lower installation costs.
• All ring circuits shall be run in the form of a
  ring looping into the terminals of the socket
  outlets and returning to same protective device.
  The circuit protection conductor (cpc) should
  also be run in a ring unless it is provided in
  form of metallic conduit or trunking.
• Typical standard circuits are tabulated as
  follows

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Q A
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The End