Download Electrical Trunking

Lincoln Robinson
Caliphor Fagan
Richard Lawrence
Wesley Esson
Anthony Gore
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.
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.
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.
Types of Trunking cont’d
 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.
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.
Rising Main Bus-Bar
Trunking
Over –head Bus-Bar
Trunking
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.
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.
 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.
Triple Compartment Trunking
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,
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.
Installation of Trunking
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.
Correct Screws Used to support Trunking to
walls
Typical Mounting Brackets used
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.
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.
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
Table 2. Space Factors for Trunking
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,