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Faculty of Engineering & Technology
Lecture 20
Electrification of Commercial
Installation
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Faculty of Engineering & Technology
Topics
• Bus bar and bus bar chambers
• Arrangement of switch fuses and bus bar strips
• Mounting arrangements of switchboards and
distribution boards
• Positioning of main switch and energy meter
• Estimation procedure and costing of commercial
installation
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Faculty of Engineering & Technology
Objectives
At the end of this lecture, student will be able to:
• Explain the Bus bar and bus bar chambers
• Decide the positioning of switchboards,
distribution boards, main switch and energy meter
• Discuss an estimation procedure and costing of
commercial installation
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Faculty of Engineering & Technology
Bus bar and bus bar chambers
Definition:
• An electrical bus bar is defined as a conductor or a
group of conductors used for collecting electric
power from the incoming feeders and distributes
them to the outgoing feeders
(Or)
• It is a type of electrical junction in which all the
incoming and outgoing electrical current meets.
Thus, the electrical bus bar receives the power
from incoming circuit and delivers the power to
outgoing circuit
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Bus bar and bus bar chambers
• The bus bar system consists the isolator and the
circuit breaker. On the occurrence of a fault, the
circuit breaker is tripped off and the faulty section
of the bus bar is easily disconnected from the
circuit
• The electrical bus bar is available in rectangular,
cross-sectional, round and many other shapes.
The rectangular bus bar is mostly used in the
power system
• The copper and aluminium are used for the
manufacturing of the electrical bus bar
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Bus bar and bus bar chambers
• Switch boards usually consist of a main switch fuse
for controlling the incoming line with a bus bar
chamber and a number of switch fuses for
controlling the outgoing circuits
• Bus bar chamber consists of bus bars which are
strips of copper or aluminium
• The incoming lines are connected to distribution
bus bars through the main switch fuse and the
load circuits are supplied from the bus bars
through the switch fuse units
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Arrangement of switch fuses and bus
bar strips
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Arrangement of bus bar strips
• In a bus bar chamber there are fixed four bus bars
of which three are for the three phases and the
fourth for the neutral
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Arrangement of bus bar strips
• The size of aluminium or copper bus bars can be
calculated based on the current carrying capacity
• It is usually made up of 16 SWG metal sheet
• Inside the bus bar chamber, the bus bars strips are
mounted on bakelite or other insulator supports
to prevent the deflection of bus bars strips by their
own weight
• Each switch fuse unit is connected to the bus bar
strips by means of strips or wires of the same
material as the bus bar
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Arrangement of bus bar strips with
insulator supports
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Faculty of Engineering & Technology
Mounting arrangements of
switchboards and distribution boards
• Switchboards or distribution boards can be
mounted on the wall or an the floor. Usually any
type of mounting frame can be made with suitable
angle iron
• The size of angle iron depends upon the weight
and size of the switchboard or distribution board
to be mounted on the frame
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Arrangement of angle iron wall
mounting frame
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Schematic arrangement of power distribution in a
large building using sub-distribution boards
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Positioning of main switch and energy
meter
• The energy meter should be installed at such a
place which is readily accessible to the consumer
as well as to the supply authority
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Faculty of Engineering & Technology
Positioning of main switch and energy
meter
• Energy meter should be installed at a height
where it is convenient to note the meter reading
• The main switch for isolating the supply to the
building provided immediately after the energy
meter
• The cut-out contains a fuse wire so that if the
consumer draws heavier current than the rating of
the meter, the fuse will blow off thus saving the
meter from damage
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Earthing, selection of earth electrodes
and earth conductors
• For earthing of installations in buildings or small
industries or residential premises only GI pipe or
rod earth electrodes are used
• GI plate earth electrodes can be used for industrial
loads upto 30HP
• For industrial loads above 30HP or power houses
or substations copper plate earth electrodes are
recommended
• The size of earth continuity conductor should not
be less than 14SWG copper
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Faculty of Engineering & Technology
Size of earth wire/conductor for
various loads
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Estimation procedure and costing of
commercial installation
The following steps to be followed for the electrical
installation in commercial building:
• Decide the number of sub-circuits
• Decide the size and rating of switch boards and
distribution boards
• Select the size of cables
• Select the bus bar and bus bar chamber
• Mounting arrangement of switch boards and
distribution board
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Summary
• Function of bus bar and bus bar chambers are
discussed
• Positioning of switchboards, distribution boards,
main switch and energy meter are discussed
• Estimation procedure and costing of commercial
installation are discussed based on load current
