Installation of Transmission and Distribution Lines

1. Installation of Transmission and
Distribution Lines

2. Erection of steel structures
 The erection of steel structures in transmission and distribution lines involves the installation
of towers, poles, and other supporting structures that carry electrical conductors and cables
used to transmit and distribute electrical power over long distances.
 These structures are a crucial component of the power grid, enabling the safe and efficient
transmission of electricity.
Tower Pole

3. 1. Design and Engineering: Before any construction begins, detailed engineering and design work is
carried out. This includes determining the types and heights of towers or poles needed, the spacing
between them, and the conductor configuration.
2. Site Preparation: The construction site is prepared, which might involve clearing vegetation,
excavating for foundations, and creating access roads for construction equipment.
3. Foundation Installation: In some cases, tower foundations might be required. These are typically
concrete foundations that anchor the towers securely to the ground. The foundation design is
critical to the structural stability of the tower.
4. Tower Erection:
• Assembly: Tower components are typically prefabricated off-site. These components include
tower legs, cross-arms, braces, and other structural elements.
• Transportation: Towers are transported to the site, often in sections, and then assembled on-
site.
• Erection: Cranes and other specialized equipment are used to lift and position the tower
components. Bolts or welding are used to connect the components securely.

4. 5. Conductor Installation:
• Stringing: Conductors (wires or cables) are strung between the towers. Stringing involves using pulleys,
tensioning equipment, and special tools to install the conductors along the designated path.
• Clamping: The conductors are securely clamped to the insulators on the tower cross-arms.
6. Insulator Installation: Insulators are placed on the tower to prevent electrical current from flowing through the
structure. These insulators are made of materials that are highly resistant to electricity.
7. Grounding and Bonding: Proper grounding and bonding are essential to ensure the safety of the transmission and
distribution system. Grounding systems are installed to direct lightning and fault currents safely into the ground.
8. Testing and Commissioning: After the erection of the steel structures and installation of conductors, thorough
testing is conducted to ensure that the system functions as intended. This includes checking for electrical continuity,
insulation resistance, and other parameters.
9. Safety Measures: Safety measures are paramount throughout the construction process. Crews working on the
transmission and distribution lines need to follow strict safety protocols to prevent accidents and injuries.
10. Environmental Considerations: Construction in environmentally sensitive areas might require additional
measures to protect local ecosystems and wildlife.
11. Maintenance and Monitoring: Once the steel structures are erected and the transmission and distribution lines
are operational, regular maintenance and monitoring are necessary to ensure the continued reliability of the system.

5.  There are 4 main methods of the erection of steel transmission towers which are described below:
1. Build-up method or Piecemeal method- involves assembling the transmission tower piece by
piece directly at the construction site. This method requires the tower components, such as steel
sections and structural members, to be transported to the site and then assembled one by one.
2. Section method- The section method is similar to the build-up method, but instead of assembling
each individual piece on-site, the tower sections are pre-assembled at a different location and then
transported to the construction site as larger segments.
3. Ground assembly method- The ground assembly method involves constructing the transmission
tower horizontally on the ground near the installation site. Once the tower is fully assembled in
this horizontal position, it is then raised to its vertical position using specialized equipment such
as cranes.
4. Helicopter method- This method is often employed in remote or difficult-to-access locations,
such as mountainous regions or areas with limited road infrastructure. Helicopters can carry tower
sections and components directly to the installation site, bypassing the need for ground-based
transportation and assembly.

7. Main Towers Used in Transmission of Power
 Tangent towers-
• They are most commonly found in areas
where the transmission line follows a
straight path.
• Tangent towers are designed to carry
the weight of the conductors and
maintain proper tension in the lines.
• About 85% of towers in transmission
line are of this type.
• The insulator used in these towers are
provided vertically.

8. Angle tower
Anchored towers-
• These are used at the endpoints of a
transmission line or at locations where
the direction of the line changes
significantly.
• Play a crucial role in securely
anchoring the transmission line and
managing the tension at the ends of
line.
• Used to pass over highways,
communication lines and small rivers.
• It should be of robust and strong
design with anchor and guy for
additional strength.
• Examples- Angle towers, Dead-end
towers, transposition towers
Dead end tower
Transposition tower

9. Types of Poles
Pole provide support to insulators,
conductors of overhead (O.H) lines.
 Single pole and double pole
 The poles are of Reinforced
Cement Concrete (RCC), Steel
sections, or wood.
 Steel tubular sections are more
costly as compared to wood and
RCC poles.

10. Connecting jumpers
 “Jumper" generally refers to a short piece of conductor, often in the form of a wire or cable,
used to establish a temporary or permanent connection between two points. Jumpers can
serve various purposes, such as connecting two parts of a circuit, bypassing a component,
or linking two conductors in a transmission line.

11.  Jumpers can be used in transmission lines for a variety of reasons:
1. Fault Bypass: If a fault is detected in a section of a transmission line, a jumper can be used
to bypass the faulty section temporarily while repairs are being made. This helps maintain the
continuity of power transmission.
2. Isolation: Jumpers can be used to isolate a section of the transmission line for maintenance
or repairs. By disconnecting a portion of the line with jumpers, the rest of the system can
continue to operate.
3. Testing and Troubleshooting: Jumpers can be used to create specific test configurations for
troubleshooting purposes. They can help engineers and technicians isolate parts of the system
to identify the source of an issue.
4. Switching: In some cases, jumpers might be used to switch between different configurations
or paths in a transmission system. This can help reroute power flow as needed.
5. Temporary Connections: Jumpers can also be used to establish temporary connections
between transmission lines, equipment, or substations. This might be necessary during
system upgrades or changes.

12. Tee-off points
 “Tee-off points" typically refer to
specific locations or points along a
power distribution or transmission
line where additional connections are
made to supply power to various
loads or distribute electricity to
different destinations.
 These connections are often made
through branching lines that resemble
the letter "T," hence the term "tee-
off."

13.  Here are a few key points about tee-off points:
1. Distribution Networks: Tee-off points are commonly found in distribution networks, where
electrical power generated at a central source is distributed to various consumers or loads.
2. Substations: In larger electrical distribution systems, tee-off points might be associated with
substations. Substations receive high-voltage power from transmission lines and then distribute
it at lower voltages to local loads. The connections made at substations are often tee-off points.
3. Feeder Lines: A feeder line is a primary power line that carries electricity from a substation to a
specific area. Tee-off points can be established along feeder lines to branch off power to
different neighborhoods or industrial zones.
4. Load Management: Different branches can be controlled separately, enabling operators to
manage power distribution based on demand fluctuations.
5. Reliability and Redundancy: If one section of the distribution network experiences an issue,
power can be rerouted through alternate tee-off connections to maintain supply to critical loads.
6. Control and Automation: Modern distribution systems often use smart grid technologies. Tee-
off points can be remotely controlled and monitored, allowing for more efficient management
of the distribution network.
7. Safety and Isolation: Tee-off points can be designed to isolate certain sections of the
distribution system for maintenance and repairs without affecting the entire network.

14. Conductor joints and dead ends
 Conductor joints refer to the points where two separate sections of a conductor are connected together.
 Conductor joints need to be properly made and maintained to ensure a continuous and low-resistance
electrical path. Poorly made joints can result in increased resistance, leading to overheating and potentially
causing fires or other electrical issues.
 Different methods are used to create conductor joints, including soldering, crimping, welding, and mechanical
connectors.
 Conductor joints are essential for several reasons:
1. Long-Length Transmission Lines: Transmission lines can stretch over vast distances, and it's often impractical to
manufacture a single continuous conductor of such lengths. Therefore, conductor joints are used to connect shorter
sections of conductor together, allowing for efficient transportation and installation.
2. Maintenance and Repairs: Over time, power lines can experience wear and tear due to various factors such as
weather conditions, vibrations, and thermal cycling. When damage occurs, conductor joints allow for the replacement
of specific sections of the conductor without the need to replace the entire length.
3. Expansion and Upgrades: As power demand increases, new transmission lines may need to be added or existing ones
upgraded. Conductor joints facilitate the extension of the existing network or the installation of higher-capacity
conductors.
4. Flexibility: Conductor joints provide flexibility in designing and adapting transmission and distribution systems to
different layouts and topographies.

15.  A "dead end" refers to the point where a
power line terminates or is anchored, at
utility poles or transmission towers.
 The term can also refer to a section of
power lines that isn't connected to any
other lines.
 Dead ends are designed to secure the
power lines and provide support against
tension caused by the weight of the lines
themselves and external forces like wind.
 Dead ends typically involve hardware
components such as clamps, insulators,
and tension devices. These components
help distribute the mechanical load evenly
and prevent the power lines from sagging
excessively.
 Proper design and installation of dead
ends are crucial to maintaining the
stability and integrity of the power
distribution network.

16.  In high voltage O.H lines, different types of strain clamps are used for dead ending.
1. Single bolt strain clamp- Used for dead ending conductors medium or light duty
transmission lines.
2. Two bolts strain clamp- Used for dead ending of conductor of main distribution lines
and light distribution lines. The gripping power is more than single bolt strain clamps.
3. Multi bolt strain clamp- Used for dead ending heavy duty transmission and distribution
lines. Provides sufficient gripping power to hold heavy duty line under tension.
4. Compression type dead end clamp- Used for dead ending ACSR conductor of
transmission lines of voltages above 66 kV.

17.  Planning the route of lines
• Before deciding the line alignment, it is necessary to prepare a survey map of adjoining areas of
proposed route.
• It will help in assessing necessary details of construction with accuracy.
 Planning of a distribution system
o Distribution system is required for the distribution of electrical energy.
o Good planning is necessary for a development and long life of system and also to make maximum
use of available resources.
 Load survey
o Load survey of a particular area is carried out to find out present load requirements as well
as expected load growth over a period of 5-7 years.
o The following data should be collected:
1. Detailed map of area showing important feature.
2. The number of houses, population, and new constructions expected in area.
3. The number of shops, post office, rural health centres, panchayat offices. (present and expected)
4. 4. Details of hospitals, railway stations, public health sewerage system and water supply schemes.

18. 5. Cultivated area, number of wells, and available irrigation facilities.
6. Type and number of industries possible in area.
7. Development programme implemented and to be implemented.
Load forecasting: For this purpose, the consumers may be classified as:
Domestic consumers i.e. residential houses
Commercial consumers i.e. shops, schools, hospitals, hotels.
Industrial consumers: small industries (up to 20 kW), medium
industries (up to 100 kW), Large industries (above 100 kW),
municipal consumers, agricultural consumers.

19.  Survey of Lines
It is necessary to survey the area in order to determine the route along which a line is to be laid.
The proposed route should be shortest practicable distance.
o First step- Select the route and plot it on a map to a large scale.
o Second step: Conduct a walk over survey to determine the topography of the area and any
obstacles likely to come across.
o Detailed survey to determine the quantity of material required for the line construction.
o Route of line should be selected along an available road in the area as it will help in delivery
of material as well as construction and maintenance.
o While selecting route, following areas should be avoided:
Wells Bridges
Low lying
areas
Water
logged areas
Gardens
Trees
Building
containing
explosives
Aerodromes
Urban
development
areas

20.  There are some special problems which must be considered when route of line crosses a river or
railway line or national highway or telecommunication line or passes through a forest.
• River crossing
 A data of high flood levels of at least 20 years should be obtained from revenue authorities and the structure
are to be erected so that they remain approachable even under flooded conditions.
 For nan-navigable rivers, the transmission line structures should be designed in such a way so that the lowest
conductor should be 3 m above the maximum flood level. This is necessary because flood waters may carry
trees and their branches.

21. • Railway crossing- The regulations framed by railway authorities.
o An O.H line should be at right angles to the tracks. But a deviation to the extent of 30
degrees may be permitted under unavoidable circumstances.
o The distance between one of supporting structures and the nearest track should be equal
to the height of structure above ground level plus 3 m.
o All guards wire should be galvanised steel not less than 6 SWG for carrier wires and 10
SWG for cross-lacing.
o Minimum permissible clearance between O.H line and railway track:
Voltage Clearance between track and lowest conductor in ‘m’
Broad gauge Meter Gauge
Inside
station
Outside
station
Inside
station
Outside
station
1. Upto 650 V 7.2 7.2 6.1 6.1
2. 650 to 33 kV 10 7.6 8.6 6.4

22. • Crossing of roads
o Guarding is done below line conductors when they cross roads.
o It is crucial to ensure the safety of road users, pedestrians, and
workers.
o Two G.I. wires of size 3.15 mm are stretched under tension
between the supports on either sides of roads and fixed to the
cross arms.
o The line should not cross the road at an angle less than 60
degree.
Guarding
S. No. Type of Road Width of
Road
Min. horizontal clearance between
centre of road and line support
1 National
highway
11.6 m 7.6 m
2 State highway 9.8 m 6.7 m
3 Major district
roads
7.3 m 5.5 m

23. • Crossing of telecommunication lines
o High voltage power lines sets up electric and magnetic field in its vicinity. The communication line
under the influence of such field can experience electromagnetic or radio frequency interference, and
induced voltages.
o Power telecommunication co-ordination committee (PTCC) has set the code of practices:
 Telecommunication lines should be placed below the power lines because it requires constant attention for
maintenance.
 The preferred angle of crossing between power and telecommunication line is 90 degree. But it should not be
less than 60 degrees.
 The guard between both the lines may be fixed either to supports of power line or telecommunication line.
• Forest area- While passing from forest area, permission should be obtained from forest authorities for
carrying out the survey and for falling of trees so that minimum tree clearance is 1.8 m is obtained from
conductor.
Voltages Minimum clearance
Above 33 kV and upto 66 kV 2.4 m
Above 66 kV and upto 132 kV 2.7 m
Above 132 kV and upto 220 kV 3 m

24. Earthing of O.H lines
 All metal supports of O.H line and metallic fittings should be
permanently and efficiently earthed by:
1. Running continuous earth wire
2. Earthing each pole individually
 Ground wires or earth wires are bare conductors supported at the
top of transmission towers. They serve to shield the line and
intercept lightning stroke before it hits the current carrying
conductors below.
 Ground wires normally do not carry current. Therefore, they are
often made of steel. The ground wires are solidly connected to
ground at each tower in transmission and distribution system.
 Method of earthing- A galvanized iron rod of 20 mm dia or a
pipe of 40 mm dia is driven into ground, water is poured to keep
the soil surrounding pipe or rod moisture. Earth wire is connected
with the rod or pipe with help of a clamp. This type of earthing is
provided on ordinary soils. Where the soil is hard, charcoal and
salt layers are provided around pipe or rod in alternate layers to
reduce earth resistance which should not be more than 10
ohms.

25. Guarding of O.H lines
 A guard wire is safety cage which runs along the distribution line.
 This wire is properly earthed.
 Guarding is provided to low, medium, and H.T overhead lines so that in the event of
breakage of any phase conductor due to wind storm etc, it would first come in touch
with cradle guard wires which are earthed, making the live conductor dead by tripping
the circuit breakers.
 Guarding is necessary in O.H lines at following places:
 Types of Guarding- Cradle guarding, Cage guarding, Bird guarding
Road
crossing
Railway
crossing
Rivers Canals
Telephone
lines

26.  Cradle guarding- It is provided when the conductors are in horizontal formation.
 Cage guarding- It is provided when the conductors are in vertical formation.
 Bird guards- To overcome the fault conditions caused due to birds coming in contact with E.H.T
lines bird guards are fixed over the suspension insulator strings in the saw tooth form.

27. Spacing of conductor
 The formula for conductor spacing is based on
line voltage, span, weight of conductor, wind
pressure on conductor and direction of swing.
 Generally, greater the span length, more should
be the spacing distance between conductor for
same working voltage to avoid touching
between them in storms.
 For aluminium and its alloys,
Spacing = √d + V/150 meters
 For other material,
Spacing = 0.75 √d + V/150 meters
d = sag in meters, V = Line voltage in kV

29. Type of Conductors
 In the early days conductor used on transmission lines were usually Copper, but Aluminium Conductors have
Completely replaced Copper because of the much lower cost and lighter weight of Aluminium conductor.
 The symbols identifying different types of Aluminium conductors are as follows:-
1. AAC : All Aluminium conductors.
2. AAAC : All Aluminium Alloy conductors
3. ACSR : Aluminium conductors, Steel-Reinforced
4. ACAR : Aluminium conductor, Alloy-Reinforced
 AAAC have higher tensile strength than the conductor of AAC, ACSR consists of a central core of steel
strands surrounded by layers of Aluminium strands. ACAR has a central core of higher strength Aluminium
Alloy surrounded by layer of Electrical-Conductor-Grade Aluminium.
 Very recently, a new type of composite using ceramic fibers in a matrix of aluminum has been introduced that
has lighter weight and higher strength. These are ACCR cables (aluminum conductor composite reinforced).
 This new conductor has the advantage of high strength even at elevated temperatures, and the addition of
zirconium to the aluminum alloy makes it more resistant to degradation at high temperatures.

30. Standard Sizes of Conductor for Lines of Various
Voltages

31. Configurations of conductor
1. Single-Circuit Configuration: In this configuration, each tower or pole carries a single set of conductors for
a single phase. Single-circuit lines are suitable for lower voltage levels and simpler installations.
2. Double-Circuit Configuration: In a double-circuit arrangement, two sets of conductors for different phases
are strung on the same set of towers or poles. This configuration is commonly used to increase the capacity of
transmission lines while minimizing the number of structures.
3. Bundle Conductors: Bundle conductors involve grouping two or more individual conductors together in a
single phase. Bundling reduces the overall inductance, improves current-carrying capacity, and mitigates the
effects of corona discharge.
4. Quad-Bundle Configuration: This is an extension of the bundle conductor concept, where four conductors
are grouped together. Quad-bundle configurations are often used for extra-high voltage transmission lines.

32. Insulators
 Provide electrical insulation and mechanical support.
 They prevent electric current from flowing between the conductive
wires and the supporting structures.
 These are meant for supporting O.H conductors and are fixed on cross
arms. Various types are:
1. Pin Insulator- Used in power networks up to 33 kV system.
Support conductors in intermediate poles but do not take any
tension.
2. Suspension Insulator- The numbers of insulators are connected in
series to form a string and the line conductor is carried by the
bottom most insulator. Each insulator of a suspension string is
called disc insulator because of their disc like shape. Each
suspension disc is designed for normal voltage rating 11KV, so by
using different numbers of discs, a suspension string can be made
suitable for any voltage level.
3. Strain Insulator- When suspension string is used to sustain
extraordinary tensile load of conductor it is referred as strain
insulator. When there is a dead end or there is a sharp corner in
transmission line, the line has to sustain a great tensile load of
conductor or strain.
Pin

33. 4. Post Insulators: Post insulators are used to support busbars and other equipment in substations.
They are mounted vertically and are designed to withstand both electrical and mechanical stresses
in a substation environment.
5. Glass insulator- These insulators were prevalent during the earlier days of electrical distribution
and transmission systems. However, due to advancements in materials and technology, other types
of insulators, such as porcelain and composite insulators, have largely replaced glass insulators in
modern power systems.
6. Stay Insulator- Used in low voltage lines to provide electrical insulation and mechanical
support to stay wires in power distribution and transmission systems. Stay wires are used to provide
additional support to utility poles or structures, preventing them from leaning or falling due to the
tension forces applied by the overhead conductors.
7. Shackle Insulator- Used in distribution networks that works with low voltage is known as a
shackle insulator. At present, the usage of this insulator has decreased because of the underground
cable used in distribution purposes.

35. Anti climbing devices and danger plates
 Anti-Climbing Devices:
• Anti-climbing devices are installed on utility poles,
transmission towers, and other structures to discourage
individuals from attempting to climb or access the
equipment.
• Climbing on power structures poses serious risks,
including the potential for electric shock and accidents
that can lead to injury or death.
• Anti-climbing devices are designed to create physical
barriers that make it difficult or nearly impossible for
unauthorized personnel to climb the structure.
• Common types of anti-climbing devices include:
1. Barriers and Guards: These are typically metal or
plastic structures that cover the lower portions of poles
or towers, making it difficult for people to grip or scale
the structure.
2. Razor Wire : These types of barbed wire are used as a
deterrent on the perimeter of power structures, making
climbing extremely challenging and dangerous.

36.  Danger plates, also known as warning signs or
caution signs, are prominently displayed near high-
voltage equipment and overhead lines to alert
people to the potential hazards.
 These plates provide clear information about the
presence of dangerous electrical equipment and the
risks associated with proximity or contact.
 Danger plates typically include text, symbols, or
pictograms that convey the message of danger.
 Some common information found on danger plates
may include:
1. High Voltage Warning: The plate may include text
or symbols indicating the presence of high-voltage
equipment or overhead lines.
2. Electrical Hazard: Warnings about the risk of
electric shock or electrocution.
3. No Trespassing: Indicating that unauthorized
access is prohibited.
4. Safety Instructions: Guidelines on safe behavior
around the equipment, such as maintaining a safe
distance.
5. Emergency Contact Information: Contact details
for reporting emergencies or unsafe conditions.

37. Size of conductor
 Factors which decides the size of the conductors designed for distribution system are given
below:
• Current carrying capacity of the conductor
• Tensile strength of the conductor
• While considering current carrying capacity of the conductor the maximum temperature
which it can withstand easily has to be taken into consideration.
• For aluminum cored conductors this temperature is 75 degrees. If temperature increases
beyond this limit the conductor starts annealing and its tensile strength is reduced. After
sometime, the conductor will melt and will be broken.
• The tensile strength of conductor is sufficient to withstand the mechanical forces acting on it
due to length of span, wind and other atmospheric conditions.
• If it is not found suitable to withstand such pressures then a higher conductor size should be
taken.

38. Guys
 A galvanized steel wire either single or stranded, one end of
which is attached to a structure (pole) and other end is
attached to anchor.
 Guys is used in case of all angle and tension supports such as
wood poles, RCC poles, etc.
 Overhead lines poles at terminals angles and tee offs have a
tendency to be pulled away from the true vertical position.
Therefore to overcome this, guys are used.
 Digging of Guy Pit- The guy rod is held by the guy plate
inside the ground. The guy pit must be dug carefully. The
angle of guy must be between 30°- 45 °.

39. Testing and Commissioning of O.H Distribution Lines
 General Inspections- Before the line is energised, visual inspection of the line should
be carried out to check that all nuts and bolts are tight and the insulators are in position
at each support. The earth connections should also be checked properly.
 Testing- After the erection of 11 kV at L.T. lines the following tests should be
conducted before commissioning of lines:
a) Conductor Continuity Test- To verify that each conductor of O.H line is
electrically properly connected. Electrical continuity of line is checked with the
help of a continuity tester and or a multimeter set to continuity mode.
b) Insulation Resistance Test-
i) For L.T line of 115V/240 V: Each phase and neutral of line should be tested
for leakage with a 500 V Megger. Insulation of each conductor should not
be less than 2 MΩ.
ii) For 11 kV line: Each phase of line should be tested for leakage with a 1000
V megger. Insulation resistance of each conductor should not be less than
50 MΩ.
c) Earth Resistance Test- It should be carried out with an earth resistance tester on
the earth wire on 3-poles per km of the line on metallic fittings. If the resistance is
higher than 10Ω, the earthing arrangement should be improved to bring down the
earth resistance to 10Ω.

40.  Commissioning of the Lines- After checking the line and checking its actual conditions the chief
electrical inspector of state is informed that line is ready for his inspection. The 11 kV lines should
first be energised at L.T voltage and after a few hours of satisfactory operation, the line may be
commissioned at rated voltage.
 Routine Inspection of O.H lines- All O.H lines should be patrolled regularly each month by
inspector at ground level when the line is live. The important parts to be checked:
1. Supports- Check metal supports, wooden poles, PCC and RCC poles. Check concrete
foundation, soil erosion, pole alignment, any leakage, cracks.
2. Cross arms- These may get rusted or tilted (metallic crossarm) or decaying due to rot
(wooden crossarm).
3. Insulators and fittings- Check for any defects-broken, tilted insulators, accumulation of dust,
rusting of fittings, burnt spots on glaze of insulator. Damaged insulator should be replaced and
dirty ones should be cleaned after disconnecting lien from supply.
4. Conductors and earth wires- Clearance between phase wires and clearance with ground
should be checked. In case of sag it should be corrected after disconnecting the line from
supply.
5. Conductor fittings and joints- Looseness of binding on insulators and at joints, slip of
conductor from insulator sheet, broken strands, burnt jumpers and loose fittings on clamp.

41. 6. Guys and their accessories- Loose guys, broken chipped of guys insulators, earthing arrangement of
guys broken and missing, corrosion of guy rods, condition of guy anchoring.
7. Gang operated switch or fuse unit on 11 kV line- Defective switch, missing or broken earth wire,
cracked or chipped insulator, burning or overheating of contacts, damaged arcing contacts.
8. Lightning arresters- The lines lead of lightning arrestor should be firmly connected with the phase
wire. Earth connection should be tight and earth resistance should be less than 10 ohms.
9. Tree clearance- Trees or branches coming close to lines should be trimmed. A minimum clearance of
1.8 m should be maintained. Also remove grass from neighbourhood of line during inspection.
10. Bird Nests- These should be removed from O.H lines, crossarms and change damaged insulators.
11. When soil is very loose. Clamps should be used around the pole beneath the ground.
12. Vertical alignment of pole should be checked.
13. Earth electrodes should be watered from time to time.
14. Earth resistance should be checked from time to time.
15. Sag should be checked for permissible units.
16. Stay assembly should be checked for proper tension.
17. Annual check- Inspect individual tower. Inspect O.H electrical fittings including insulators and
mechanical connectors. Wash insulator with water. Replace cracked insulators.

42. Service connection
 The cable (overhead or underground) which supplies electric power from the supply pole to
consumer’s terminals is called service mains or service line.
 In single phase supply (domestic loads), the service main has three wires, namely phase wire, neutral
wire, and earth wire, running from supply at pole to consumer’s premises upto energy meter
installed.
 In three phase supply (industrial loads), five wires run from service pole to consumer terminals.
Three wires are for three phases, fourth wire is neutral and fifth wire is earth wire.
1. Low voltage supply at 230 V AC for demand of power not exceeding 4 kW. (houses and shops)
2. Medium voltage supply at 400 V AC for demand of power not exceeding 50 kW. (Residential
building and small factory)
3. High voltage supply at 3.3 kV, 6 kV, 11 kV and 33 kV AC for demand of power above 50 kW.
(multi storey building in big industry)

43.  In construction of O.H service line, the following points should be kept in mind:
1. The service span should be limited to 35 m.
2. The service line should be fed of only from the pole and not from mid span.
3. The pole selected for teeing off should be straight properly.
 Service line- A line connecting the consumer installation to a distributor. It is the last line of the network
transmitting power from the power station to consumer.
 There are two types of L.T service lines.
i. Bare wire service line- AAC is used for phase and neutral and most used earth conductor is number 8 SWG G.I
wire.
ii. Catenary wire and insulated cable line- Weather proof cable should be used for aerial cable. Aerial cable
should not have any joints. Only G.I wire of hard drawn quality of number 8 SWG should be used for earth wire.
The aerial cable should be treated through reel insulator.
 There are two types of service connections.
i. Overhead service connections
ii. Underground service connections

44. i. Overhead service connections-
• If consumer premises is more than 45 m away from nearest
distribution line support then service connection will be by O.H
bare conductors. If the consumer premises is less than 45 m away
then service connection is by means of weather proof or PVC
cables.
• In double storey building, if service connection is by bare
conductor, then service bracket is placed into wall. Wires are
taken from service pole to shackle insulators and fixed to bracket
connections and then taken to energy meter by weather proof or
PVC cables.
ii. Underground service connections-
• This is used where heavy loads above 25 kW are to be applied.
• Paper insulated cable terminates at each end into a cable box.
• To protect cable from any mechanical damage it is run through
G.I pipe of 2 m length, where it rises at pole and at service board.
• Cable is held to pole by means of pole clamp.

45. Service fuses
 Pole fuse- An aerial fuse provided on pole to protect the distribution system and the
connected equipment from overcurrent and short circuit.
 Supplier’s fuse- The aerial fuse protects only service cable and not energy meter. To
protect the energy meter, supplier fuse is used. Each consumer have independent supplier
fuse.
 Switch fuse- For controlling the supply to the consumer, double pole linked switches are
used to protect wiring between main switch and distribution board.
 Kit-kat fuse- These are inserted in distribution board. The size of kit kat fuse wire depends
upon maximum current of circuit. In short circuit or heavy load, it protects cables from
being damaged.

46. Installation of energy meters
 The number of meters required for any particular installation will depend mainly
upon tariffs and methods of payment offered by supply authority, and chosen by
consumer.
 At present a number of different types of tariffs is offered by supply authority in
various parts of country and involves various methods of metering.
 The size of energy meter chosen for any particular premises must be large enough to
deal adequately with the load to be registered, but not large as to be uneconomic at
light loads.

47.  Installation of energy meter-
• For most installations, energy meter are fixed to wooden boards and care should be taken that
these boards are mounted on a rigid structure like a wall.
• Situations where meters might receive shock transmitted from slamming a doors etc. might be
avoided.
• The energy meter should be installed in consumer’s premises and near to the cut out as possible.
• They should be easily accessible in order to provide consumer with minimum amount of trouble
in operating the meters.

48.  Special metering arrangement- In factories and other large industrial or commercial premises
the particular tariffs in operation frequently requires special metering arrangements like-
Maximum demand metering- For many commercial and industrial customers, electricity bills
are calculated not only based on total energy consumed (measured in kWh) but also on the
highest level of power demand. MD metering uses a predefined demand interval, usually 15, 30,
or 60 minutes. During this interval, the meter records the highest demand observed.
Kilo-volt ampere hour metering- This is often used by utility companies and large consumers
of electrical energy for billing purposes. It can also provide load profiling information, helping
users understand their power consumption patterns. A low power factor indicates inefficient use
of electrical energy due to reactive power consumption. kVAh meters help identify and monitor
power factor issues.