Electrical Trunking

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Electrical Trunking

• Lincoln Robinson
• Caliphor Fagan
• Richard Lawrence
• Wesley Esson
• Anthony Gore

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What is Electrical Trunking?

• Trunking is an enclosure provided for the
  protection of cables which is normally square or
  rectangular in cross-section, having one
  removable side. Trunking may be thought of as
  simply a larger and more accessible conduit
  system. It is available in two ranges, ordinary
  wiring trunking and bus-bar trunking. The
  ordinary system is further available in either
  metal or PVC.

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Types of Trunking

• Metallic Trunking
• Metallic Trunking is formed from mild steel
  sheet, coated with grey or silver enamel paint
  for internal use or a hot-dipped galvanized
  coating where damp conditions might be
  encountered.
• PVC Trunking
• The main areas in which PVC trunking is used are
  domestic and office premises. All necessary
  fitting are available to complete any shape of
  run with little difficulty. The accessories are
  usually secured to the lengths of Trunking with
  a PVC solvent adhesive.

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Metal Trunking

• Metal trunking is used extensively in engineering
  premises. It allows a large number of cables to
  be drawn into one system with relative ease and
  because of its accessibility enables changes or
  additions to circuits to be made with the minimum
  of effort. As with conduit, it is available
  either painted or galvanized. A whole range of
  fittings is available, enabling the most
  difficult runs to be constructed. It is available
  in many different sizes and designs. For example,
  compartment trunking allows the segregation of
  certain currents, and support of cables in
  vertical runs.

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Types of Trunking contd

• Mini-trunking is very small PVC trunking, ideal
  for surface wiring in domestic and commercial
  installations such as offices.
• A trunking manufactured from PVC or steel and in
  the shape of a skirting board is frequently used
  in commercial buildings such as hospitals,
  laboratories and offices.

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Bus-bar trunking

• There are two main types of bus-bar trunking, the
  Overhead type of bus-bar used for distribution in
  industrial premises, and Rising-main trunking.
  Overhead bus-bar trunking is ideal for
  distribution in factories. It is run at high
  level and the tap-off boxes enable machinery to
  be moved easily. When connected in the form of a
  ring and incorporating section switches, this
  system enables parts of the trunking to be
  isolated when necessary, without all machines
  losing supply.

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Rising Main Bus-Bar Trunking
Over head Bus-Bar Trunking
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Cutting and Drilling Trunking

• It is often necessary to cut or drill trunking.
  After cutting, all edges should be filed to
  remove sharp metal. Burrs left after the drilling
  of a hole should also be filed away. When
  high-speed twist drills are being used, a
  lubricant should be applied this aids the
  drilling process and prolongs the life of the
  drill. A lard oil such as tallow is recommended
  for use with steel. (No lubricant is needed when
  drilling PVC.) It is often necessary to cut large
  holes in order to connect conduit into the
  trunking system this may be achieved by the use
  of a circular hole saw or a pressure-type hole
  cutter. After cutting, all hole edges must be
  filed smooth and conduit entries Bushed.

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Segregation of Cables

• Where an installation comprises a mixture of
  low-voltage and very low voltage circuits such as
  mains lighting and power, fire alarm and
  telecommunication circuits, they must be
  separated or segregated to prevent electrical
  contact (IEE Regulation 528.1). For the purpose
  of these regulations various circuits are
  identified by one of two bands as follows
• Band I telephone, radio, bell, call and intruder
  alarm circuits, emergency circuits for fire alarm
  and emergency lighting.
• Band II mains voltage circuits.
• N.B. Multi-compartment PVC trunking cannot
  provide band segregations since there is no metal
  screen between the Bands. This can only be
  provided in PVC trunking if screened cables are
  drawn into the trunking.

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• Single Compartment Trunking Can be used when one
  type of cable i.e. electrical or data or
  telephone cables.
• Double Compartment Trunking Can be used when two
  type of source cable i.e. electrical data
  cables or electrical telephone cables.
• Triple Compartment Trunking Can be used when all
  three types of source cable i.e. electrical,
  data, and telephone cables.

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Triple Compartment Trunking
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Construction

• A trunking is an enclosure provided for the
  protection of cables which is normally square or
  rectangular in cross-section, having one
  removable side. Trunking may be thought of as a
  more accessible conduit system and for industrial
  and commercial installations it is replacing the
  larger conduit sizes. A trunking system can have
  great flexibility when used in conjunction with
  conduit the trunking forms the background or
  framework for the installation,

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• with conduits running from the trunking to the
  point controlling the current using apparatus.
  When an alteration or extension is required it is
  easy to drill a hole in the side of the trunking
  and run a conduit to the new point. The new
  wiring can then be drawn through the new conduit
  and the existing trunking to the supply point.

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Installation of Trunking
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Trunking Support

• Trunking may be secured direct to a surface or
  suspended by means of brackets.
• As trunking material is thin, there is no room
  for countersunk holes. Roundhead screws are
  suggested, unless of course the fixing surface
  requires bolts. There are occasions when the
  trunking has to be suspended by means of
  brackets.

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Correct Screws Used to support Trunking to walls
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Typical Mounting Brackets used
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Space Factor

• The ratio of the space occupied by all the cables
  in a conduit or trunking to the whole space
  enclosed by the conduit or trunking is known as
  the space factor. The space factor for cables
  within a trunking should not exceed 45,this
  means that the cables must not fill more than 45
  of the space enclosed by the trunking.

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Calculating Space Factor

• To calculate the size of trunking required to
  enclose a number of cables
• Identify the cable factor for the particular size
  of conductor. See Table 1
• Multiply the cable factor by the number of
  conductors to give the sum of the cable factors.
• Consider the factors for trunking and shown in
  Table 5.4. The correct size of trunking to
  accommodate the cables is that trunking which has
  a factor equal to or greater than the sum of the
  cable factors.

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Table 1. Trunking, Cable Factors. Adapted from
the IEE On Site Guide
Note (i) These factors are for metal trunking
and may be optimistic for plastic trunking where
the cross-sectional area available may be
significantly reduced from the nominal by the
thickness of the wall material. (ii) The
provision of spare space is advisable however,
any circuits added at a later date must take into
account grouping
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Table 2. Space Factors for Trunking
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Application

• Trunking can be for both indoors and outdoors ,
  ranging from Domestic, Commercial and Industrial
  purpose Many applications includes decorative
  skirting in homes, lighting fixtures in
  restaurants and departments store,

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