Cable Construction & Cable Selection- Part:3

(9) Armoring:

  • Code: IS: 7098 / IS: 3975 / IEC:60502 / BS:6622/BS:7835.
  • Material: metallic or non-magnetic Alumimium, Steel wire/strip.
  • Used for : LV, MV & HV Cables
  • The armor provides mechanical protection against crushing forces.
  • Armor also can serve as an Earth Continuity Conductor (ECC).
  • The armoring type could be:
  • Mechanical protection of the cable is provided by a single layer of wire / Strip strands laid over the bedding. Steel wire / Strip is used for 3-core or 4-core cables, but single-core cables have aluminum wire armoring.
  • When an electric current passes through a cable it produces a magnetic field (the higher the voltage the bigger the field). The magnetic field will induce an electric current in steel armor (eddy currents), which can cause overheating in AC systems. The non-magnetic aluminum armor prevents this from happening.
  • Magnetic Material’s armoring for 3Ph System: With 3-core or 4-core cables the vector sum of the currents in the conductors is zero, and there is virtually no resultant magnetic flux. In Multi-core armored cables have either single layer of Galvanized Steel wire Armor or Galvanized steel strip applied over inner sheath with left hand lay.
  • Non Magnetic Material’s armoring for 1Ph System: This is not so however for a single-core cable, where eddy-current heating would occur if a magnetic material was used for the armoring. The material has to be non magnetic for armoring as in this case of return current is not passing through the same cable. Hence it will not cancel the magnetic lines produced by current. These magnetic lines which are oscillating in case of A.C. systems will give rise to eddy currents in magnetic armoring and hence armoring will become hot, and this may lead to failure of the cable. Hence Single core cables for use on A.C systems are armored with single layer of nonmagnetic (Aluminum) material.
  • Armoring is Mostly following Type
  • SWA – Steel wire armor, used in multi-core cables (magnetic),
  • AWA – Aluminum wire armor, used in single-core cables (non-magnetic).
  • Tinning or galvanizing is used for rust prevention. Phosphor bronze or tinned copper braid is also used when steel armor is not allowed.
  • As strip construction is economical, the manufacture always provides steel strip armoring unless wire armoring is specified.
  • As per IS: 1554 Round Wire armoring is provided in cable where calculated diameter under amour is upto13mm. Above this the amour is either steel wire or steel strip of size 4.00X0.80mm.

 (10)Over Sheath (Outer Jacket):

  •  Code: IS: IS:7098 / IEC:60502 / BS:6622/BS:7835.
  • Material: PVC Flame Retardant / Flame Retardant Low Smoke / Zero Halogen (LSOH), High density Polyethylene HDPE, Halogen Free Flame Retardant (HFFR)
  • Used for : LV, MV & HV Cables
  • Purpose:
  • It is the outer protection part of the cable against the surrounding environment.
  • Protected against water ingress, Protection against termite, Protection against UV and Protection against differing soil compositions.
  • It is applied over armoring in case of armored cable and over inner sheath in case of unarmored cable called as “Outer Sheath”.
  • The standard sheath color is Black other colors such as Red , Light Blue can also be provided
  • High-voltage cables are identified by outer sheaths colored red; a black sheath indicates a low-voltage cable
  •  The following are the electrical property may be consider while selecting a outer Sheath Materials
  • Dielectric Strength: Cable Sheath may be semiconducting or insulating.
  • Discharge and Tracking Resistance: When a non shielded cable rests upon or comes into contact with a ground plane, the ground plane acts as the outer plate of the capacitor, made up of the conductor, insulation and the ground plane. Discharges and tracking may cause erosion of the Outer Sheath material.
  • Material: A major consideration in selecting Outer Sheath may be a thermoplastic or thermosetting material. Mostly a thermoplastic jacket is less expensive. However, thermoplastics will melt at some elevated temperature and, thus, could run or drip from the cable under extreme conditions.
  • Thermoset materials will not melt and run or drip at elevated temperatures.

 Comparison of Cable:

 PVC Insulated Cable:

  •  PVC insulation becomes stiff making it difficult to fold and the soft PVC loosens its softening agent over years, making it brittle and prone to rip.
  • Even at the time of disposing, burning PVC emits toxic dioxin, which is responsible for causing cancer and does, when dumped scantly dissolve
  • PVC is thin insulation mainly used in LT side cables and XLPE is thick insulation used in MV & HT cables.

XLPE Insulated Cable:

  •  Higher Current Capacity: XLPE has higher current carrying capacity as
  • Higher Temperature Withstand Capacity: It can withstand higher temperature compared to PVC cable.
  • Higher Overload Capacity: XLPE have high overload capacity.
  • Low Dielectric Constant: XLPE has lower dielectric and constant power factor.
  • Light weight & Small Bending Radius :XLPE cables are lighter in weight, has smaller bend radius, and hence lesser installation cost.
  • Higher Short Circuit Capacity: XLPE has higher short circuit rating. XLPE can withstand higher & lower temperatures insulation is usually thinner but the resistance is higher.
  • Higher Moisture Resistance: XLPE also has a higher moisture & chemical resistance.
  • Cable Installation Job for XLPE is easier than PVC insulated cables because of less Wt, less Diameter and Less Bending radius.
  • The Volume Resistivity (ohm-cm) for XLPE is way higher than the PVC cables which are of the order of XLPE cables has insulation resistance of 1000 times compared to PVC cables.

 Elastomer Insulated Cable:

  •  Elastomer cables are preferred for flexible application and in congested locations where the bending radius are very small. Elastomer cables are available from low voltage up to 33 kV grade.
  • Elastomer cables are also available with rigid copper conductors and having properties like Fire Survival, Zero Halogen and Low toxicity FS properties.

 Rubber Insulated Cable:

  •  Rubber insulation remains in the best condition after a long span of time,say,25-30 years and remain soft and pliable even when the temperature is low.
  • Rubber Cables are predominantly used in special applications like, mining, ship wiring, transportation sector and Defense applications & earth moving machines.
  • These materials have the potential to be recyclable since they can be molded , extruded and reused like plastics, but they have typical elastic properties of rubbers which are not recyclable owing to their thermosetting characteristics

Cable Construction & Cable Selection- Part:2

(5) Insulation Screen:

  • Code: IS:7098/IEC:60502/ BS:6622/BS:7835
  • Material: Extruded thermo set semi-conducting compound, Carbon paper and carbon loaded polymer.
  • Used for : Cable from 6 to 30kV (MV & HV Cables)
  • Purpose:
  • An extruded layer of semi conducting is applied over the insulation layer to insure that the electric stress is homogeneous around the insulated core. The semi conducting layer shall be firmly bonded to the outer layer of the insulation layer.
  • The Purpose of Insulation screen is same as Conductor Screen.
  • The Purpose of Insulation Screen is to reduce voltage stress at the interface between the conducting and insulating component
  • A cylindrical, smooth surface between the insulation and Metallic shield
  • Insulation screen is a layer of black cross linked semi conductive compound of approx 1mm thickness and is either fully bonded to the insulation layer, or can be “cold strippable” by hand.
  • When terminating or jointing the cables, it is necessary to remove a part of the insulation screen.

 (6) Bedding (Inner Sheath):

  •  Code: IS: 7098, 1554 / IEC: 60502 / BS: 6622 / BS: 7835.
  • Material: Thermoplastic material i.e. PVC, Polyethylene, thermosetting (CSP) compound
  • Used for : LV, MV & HV Cables
  • Purpose:
  • It could be also called inner sheath or inner jacket, which serves as a bedding under cable armoring to protect the laid up cores and as a separation sheath.
  • Inner sheath is over laid up of cores.
  • It gives Circular Shape of the cable and it also provides Bedding for the armoring.
  • IS:1554 permits following two methods of applying the Inner Sheath of thermoplastic material i.e. PVC, Polyethylene etc., Which is not harder than insulation.
  • Inner sheath is provided by extrusion of thermoplastic over the laid up of cores
  • Inner sheath is provided by wrapping at thermoplastic tape.
  • All multi-core cables have either extruded PVC inner sheath or thermoplastic wrapped inner sheath, which is compatible to insulation material and removable without any damage to insulation. Single core cables have no inner sheath.

 (7) Water blocking Taps:

  •  Water blocking is used to prevent moisture migration.
  • Water blocking tapes or Swelling powder should be applied between the conductor strands to block the ingress of water inside the cable conductor (if required).
  • Water blocking Methods to be considered are as follows.
  • Powders: Swell able powders are used as longitudinal water blocks in cables to prevent longitudinal water penetration. These powders swell and expand sufficiently upon contact with water to form a gel-like material to block the flow of water.
  • Water-Blocking Tapes: A water-blocking tape is usually a nonwoven synthetic textile tape impregnated with, or otherwise containing, a swell able powder.
  • Sealed Overlap: To ensure a seal of the overlap, hot-melt adhesives can be used. These adhesives can be extruded or pumped into the overlap seam of a longitudinally formed metallic tape before the seam is closed during cable manufacture.

 (8) Metallic Screen:

  •  Code: IS: 7098 /IEC:60502 / BS:6622/ BS:7835.
  • Material: Nonmagnetic metallic materials Copper Wire / Tape or Aluminum Wire / Strip
  • Used for : MV & HV Cables
  • Purpose:
  • Medium Voltage & High-voltage cables have an earthed metallic screen over the insulation of each core.
  • This screen consists one or multi layers of a lapped Conductive copper wires, copper tape or metallic foil, lead, aluminum helically with overlap over insulation screen.
  • The metallic shield needs to be electrically continuous over a cable length to adequately perform its functions of electrostatic protection, electromagnetic protection, and protection from transients, such as lightning and surge or fault currents.
  • (1) Shield Electromagnetic radiation: A metallic sheath is used as a shield to keep electromagnetic radiation in the Cable.
  • The main function of the metallic screen is to nullify the electric field outside of the cable – it acts as a second electrode of the capacitor formed by the cable. The screen needs to connect to earth at least at one point along the route.
  • The capacitive charging current and induced circulating currents which are generated under normal operating conditions will be drained away through the screen.
  • (2) Earth Path: It also provides a path for fault and leakage currents (sheaths are earthed at one cable end).
  • The screen also drains the zero-sequence short circuit currents under fault conditions; this function is used to determine the required size of the metallic screen.
  • Lead sheaths are heavier and potentially more difficult to terminate than copper tape, but generally provide better earth fault capacity.
  • (3) Water Blocking: The other function of Metallic sheaths is to water block and form a radial barrier to prevent humidity from penetrating the cable insulation system.
  • (4) Mechanical Protection: It also provides some degree of mechanical protection to cable.
  • Cable shields are nonmagnetic metallic materials. The two materials typically used for metallic shields are aluminum and copper. Aluminum requires a larger diameter as a wire or a thicker cross section as tape to carry the same current as copper. At equivalent current-carrying capacity, an aluminum shield will be lighter in weight but about 40% larger in dimensions

 Different Types of Metallic Screen:

 (A) Concentric Copper Wire screens /Tapes

  • Advantages:
  • Lightweight and cost effective design.
  • High short-circuit capacity.
  • Easy to terminate.
  • Drawbacks:
  • Low resistance of screen may necessitate need for special screen connections to limit the circulating current losses.
  • Does not form a complete moisture barrier unless water swell able tapes are used under and/or over the copper wires.

(B) Aluminum foil laminate

  • Advantages:
  • Lightweight and cost effective design.
  • Moisture proof radial barrier.
  • Drawbacks:
  • Low short circuit capacity.
  • More difficult to terminate – requires special screen connections.

(C) Extruded lead alloy sheath

  • Advantages:
  • Waterproofing guaranteed by the manufacturing process.
  • Excellent resistance to corrosion and hydrocarbons (suitable for oil and gas plants).
  • Drawbacks:
  • Heavy and expensive.
  • Lead is a toxic metal whose use is being restricted in some countries.
  • Limited capacity for short circuits.

Cable Construction & Cable Selection- Part:1

Cable Construction:

Parts of Cable:

  1. Conductor (For LV/MV/HT Cables)
  2. Conductor Screen (For MV/HT Cables)
  3. Filler & Binding Tapes (For LV/MV/HT Cables)
  4. Insulation (For LV/MV/HT Cables)
  5. Insulation Screen (For MV/HT Cables)
  6. Separation Tape (For MV/HT Cables)
  7. Bedding (Inner Sheath)
  8. Metallic Sheen (For MV/HT Cables)
  9. Armor (For LV/MV/HT Cables)
  10. Outer Sheath (For LV/MV/HT Cables)
  11. Water Blocking Tapes –Optional (For MV/HT Cables)
  12. Insulation Tapes–Optional (For MV/HT Cables)


(1) Conductors:

  • Code: IS:8130 / IEC 60228/ BS 6360
  • Material: Class 2 – Annealed Plain / Tinned Copper / Aluminum.
  • Used for : LV ,MV & HV Cables
  • Purpose:
  • Usually stranded copper (Cu) or aluminum (Al) is used.
  • Copper is denser and heavier, but more conductive than aluminum.
  • Electrically equivalent aluminum conductors have a cross-sectional area approximately 1.6 times larger than copper, but half the weight.
  • The size of the copper / Aluminum conductor forming one of the cores of a cable is expressed in square millimeters (mm2), and the current rating of the cable is dependent upon the cross-sectional area of each core.
  • Multi core Aluminum or copper conductor are produced by two Shapes
  • Circular Conductor: multi layers of stranded wires are assembled together to make circular shape.
  • To achieve a circular conductor, the number of strands follows a particular progression: 3, 7, 19, 37, 61, and 127 etc, the diameter of each strand being chosen to achieve the desired cross-sectional area of whole conductor.
  • Circular Shape conductor is normally available used up to 200mm2
  • Segment Conductor: Five segments of compacted conductor in triangle shape of 72 degree are assembled together with separation of non metallic tapes to reduce the skin effect which reduce the AC conductor resistance.
  • Larger sizes have conductors with the strands laid up in a segmental formation; this Cables achieves a better space factor and reduces the overall diameter of the cable. It also reduces the inductance of the cable due to decreased spacing between phases
  • Segmental conductor is normally available from 1000 mm2 and above

 (2) Conductor Screen (Semi Conductor Screen):

  • Code: IS:7098/IEC:60502/ BS:6622/BS:7835
  • Material: Extruded thermo set semi-conducting compound, Carbon paper and carbon loaded polymer.
  • Used for : Cable from 6 to 30kV (MV & HV Cables)
  • Purpose:
  • This screen consists of a lapped copper tape or metallic foil usually less than 1.0mm in thickness, which is the interface between the conductor and the insulation (PVC, XLPE).
  • The Main Purpose of Conductor Screen is to maintain a uniformly divergent electric field, and to contain the electric field within the cable core.
  • Conductor Screen is semi-conducting material because Semi-conducting materials do not conduct electricity well enough to be a conductor but will not hold back voltage. It “smoothes” out the surface irregularities of the conductor. The conductor shield makes the voltage on the inside of the insulation the same
  • Semiconducting screening materials are based on carbon black that is dispersed within a polymer matrix. The concentration of carbon black needs to be sufficiently high to ensure an adequate and consistent conductivity.
  • The incorporation must be optimized to provide a smooth interface between the conducting and insulating portions of the cable.
  • The smooth surface is important as it decreases the occurrence of regions of high electrical stress.
  • Control Electrical Field: Conductor Screen is control the electric field within the insulation and thus the same voltage gradient across it. It also avoids any interaction of the electric stresses due to the voltages on different phase conductors within the same cable.
  • Reduce Voltage Stress Conductor Screen helps to reduce voltage stress at the interface between the conducting and insulating components.
  • A typical construction for a medium voltage cable consists of an aluminum conductor covered by a screening layer, then by a polyethylene or ethylene propylene rubber insulation followed by a further screening layer.  The coefficient of expansion of the insulation layer is typically ten times greater than that of the aluminum and when the cable is at its maximum operating temperature of 90ºC, a large enough gap can formed to allow electrical discharges to occur.  The semi-conducting layer then serves to even out the stresses associated with these discharges, which would otherwise attack the insulation at specific points.


  • Uniform Electrical Field: A Black semi-conducting tape is used to maintain a uniform electric field and minimize electrostatic stresses in MV/HV power cables.
  • The external surfaces of the conductor may not be smooth, particularly for stranded conductors, so this layer provides a smooth surface at the same potential as the conductor to keep the electric field consistent all the way around the surface. Without this layer, any small peaks or troughs could cause concentrations of electrical energy which could create small arcs, and over time could erode the insulation layer and cause failure of the cable.
  • Reduce Electrical Flux line around the each core: : It Provide a cylindrical, smooth surface between the conductor and insulation
  • Semi-conducting compounds also have the effect of filling in the interstices of the conductor giving a smooth surface for the insulation.  This reduces the electrical flux lines around each individual wire that make up the conductor, which can reduce the stress by 10-15%.  

(3) Filler & Binding Tap (Laying-Up):

  • Material: Non Hygroscopic PVC / Poly propylene Fiber to maintain roundness of cable.
  • Used for : LV,MV & HV Cables
  • Purpose:
  • In case of three core cables, the three cores are laid up with polymer compound or non-hygroscopic fillers like polypropylene (PP) fillers and a binder tape is applied with an overlap to provide a circular shape to the cable.
  • These binder tapes can be of PVC or foamed Polyethylene.
  • Inner Sheath (Bedding) for Armored Cables. Extruded layer of PVC or PE is applied over the laid up cores for armored cables.

(4) Insulation:

  • Code: IS: 7098, 8130, 14494 / IEC: 60502 / BS: 6622/BS: 7835.
  • Material: PVC, XLPE, Rubber, Elastomer, EPR.
  • Used for : LV ,MV & HV Cables
  • Purpose:
  • Insulation main Purpose is to withstand the electrical field applied to the cable for its design life in its intended installed environment
  • This will be an extruded layer of XLPE, Elastomer, Rubber or PVC applied over conductor screen under triple extrusion process along with conductor screen and insulation screen.
  • There are different Type of Insulation Material used for cable but widely used are

 (A) Cross-linked polyethylene: (XLPE)

  • They are known as PEX or XLPE Cable. It is form of polyethylene with cross links.
  • XLPE creates by direct links or bonds between the carbon backbones of individual polyethylene chains forms the cross linked polyethylene structure.
  • The result of this linkage is to restrict movement of the polyethylene chains relative to each other, so that when heat or other forms of energy are applied the basic network structure cannot deform and the excellent properties that polyethylene has at room temperature are retained at higher temperatures.
  • The cross linking of the molecules also has the effect of enhancing room temperature properties.
  • The useful properties of XLPE are temperature resistance, pressure resistance (stress rupture resistance), environmental stress crack resistance (esc), and resistance to UV light, chemical resistance, oxidation resistance, room temperature and low temperature properties.
  • XLPE cables work for the working voltage of 240 V to 500 KV.
  • The Jacketing Material can be of PVC / Flame Retardant / Flame Retardant Low Smoke / Zero Halogen (LSOH).
  • Applications: Fire Survival, Under Water Cables, Underground burial, installation on trays and ducts.

 (B) Polyvinyl chloride (PVC)

  • They are known as PVC insulated cables are widely used in various fields.
  • PVC’s relatively low cost, biological and chemical resistance and workability have resulted in it being used for a wide variety of applications.
  • For electric cables the PVC is mixed up with plasticizers. PVC has high tensile strength, superior conductivity, better flexibility and ease of jointing.
  • PVC is a thermoplastic material, therefore care must be taken not to overheat it; it is suitable for conductor temperatures up to 70°C. PVC insulated cables should not be laid when the temperature is less than 0ºC because it becomes brittle and is liable to crack.
  • Applications: Low voltage copper conductor PVC cables are extensively used for domestic home appliances wiring, house wiring and internal wiring for lighting circuits in factories, power supply for office automation, in control, instrumentation, submarine, mining, ship wiring applications etc.

(C) Elastomer Insulated cable

  • These cables are suitable for use where the combination of ambient temperature and temperature-rise due to load results in conductor temperature not exceeding 90°C under normal operation and 250°C under short-circuit conditions.
  • This insulation shall be so applied that it fits closely on the conductor (with or without either separator or screen) but shall not adhere to it. The insulation, unless applied by extrusion, shall be applied in two or more layers and it is applicable to cables with a rated voltage up to 1 100 volts.
  • Applications: Welding Cables, Ship wiring cables, Pressure Tight Cables and cables for submerged connection, Railways locomotives and coach wiring cables, Mining Cables.

(D) Polyvinyl chloride (EPR).

  • For high-voltage cables the insulation is ethylene propylene rubber (EPR) and for low-voltage cables it is polyvinyl chloride (PVC).
  • EPR has good electrical properties and is resistant to heat and chemicals; it is suitable for a conductor temperature up to 85 ºC.

(E) Rubber Insulated cable

  • These are used in electric utilities such as the generation and transmission of electricity. Long service life under normal environment in Nuclear and conventionally powered generating stations plus safety considerations are the significant factors of these electric appliances.
  • When exposed to fire, Silicon offers circuit integrity, low smoke evolution, and freedom from halogen acids.

Calculate Lightning Protection for Building / Structure

Example: Calculate Whether Lightning Protection is required or not for following Building. Calculate No of Down Conductor for Lightning Protection

Area of Building / Structure:

  • Length of Building (L) = 60 Meter.
  • Width of Building ( W ) = 28 Meter.
  • Height of Building (H) = 23 Meter.

Lightning Stock Flushing Density

  • Number of Thunderstorm (N)= 80.00 Days/Year
  • Lightning Flash Density   (Ng)=69 km2/Year
  • Application of Structure (A)= Houses & Buildings
  • Type of Constructions (B)= Steel framed encased without Metal Roof
  • Contests or Consequential Effects (C)= Domestic / Office Buildings
  • Degree of Isolation (D)= Structure in a large area having greater height
  • Type of Country (E)= Flat country at any level
  • Maximum Acceptable Overall Risk Factor =0.00000001
Reference Table As per IS:2309
Thunder Storm Days / Year Lightning Flash Density (Flashes to Ground /km2/year)
5 0.2
10 0.5
20 1.1
30 1.9
40 2.8
50 3.7
60 4.7
80 6.9
100 9.2
Application of Structure Factor
Houses & Buildings 0.3
Houses & Buildings with outside aerial 0.7
Factories / workshop/ Laboratories 1
Office blocks / Hotel 1.2
Block of Flats / Residences Building 1.2
Churches/ Hall / Theaters / Museums, Exhibitions 1.3
Departmental stores / Post Offices 1.3
Stations / Airports / Stadium 1.3
Schools / Hospitals / Children’s Home 1.7
Others 1.2
Type of Constructions Factor
Steel framed encased without Metal Roof 0.2
Reinforced concrete without Metal Roof 0.4
Steel framed encased with Metal Roof 0.8
Reinforced concrete with Metal Roof 1
Brick / Plain concrete or masonry without Metal Roof 1.4
Timber framed or clad without Metal Roof 1.7
Brick / Plain concrete or masonry with Metal Roof 2
Timber framed or clad with Metal Roof
Contests or Consequential Effects Factor
Domestic / Office Buildings 0.3
Factories / Workshop 0.3
Industrial & Agricultural Buildings 0.8
Power stations / Gas works 1
Telephone exchange / Radio Station 1
Industrial key plants, Ancient monuments 1.3
Historic Buildings / Museums / Art Galleries 1.3
Schools / hospitals / Children Homes 1.7
Degree of Isolation
Structure in a large area having greater height 0.4
Structure located in a area of the same height 1
Structure completely Isolated 2


Collection Area (Ac)=(L x W) + 2 (L x H) + 2(W x H) +(3.14 x H2)

  • Collection Area (Ac) = (60×28)+2x(60×23)+2x(28×23)+(3.14x23x23)
  • Collection Area (Ac) =7389 Meter2

Probable No of Strikes to Building / Structure (P)= Ac x Ng x 10-6 No’s / Year

  • Probable No of Strikes to Building / Structure (P)= 7389x69x106 No’s / Year
  • Probable No of Strikes to Building / Structure (P)= 05098 No’s / Year

Overall Multiplying Factor (M) =A x B x C x D x E

  • Application of Structure (A)= Houses & Buildings as per Table Multiplying Factor = 0.3
  • Type of Constructions (B)= Steel framed encased without Metal Roof as per Table Multiplying Factor =0.2
  • Contests or Consequential Effects (C)= Domestic / Office Buildings as per Table Multiplying Factor =0.3
  • Degree of Isolation (D)= Structure in a large area having greater height as per Table Multiplying Factor =0.4
  • Type of Country (E)= Flat country at any level so as per Table Multiplying Factor =0.3
  • Overall Multiplying Factor (M) =0.3×0.2×0.3×0.4×0.3
  • Overall Multiplying Factor (M) =0.00216

Overall Risk Factor Calculated (xc)= M x P

  • Overall Risk Factor Calculated (xc)= 0.00216 x0.05098
  • Overall Risk Factor Calculated (xc)= 000110127

 Base Area of Structure (Ab) = (LxW)

  • Base Area of Structure (Ab)=60×28
  • Base Area of Structure (Ab)=1680 Meter2

Perimeter of Structure (P) =2x (L+W)

  • Perimeter of Structure (P)=2x(60+28)
  • Perimeter of Structure (P)=176 Meter

Lightning Protection Required or Not

  • If Calculated Overall Risk Factor Calculated > Maximum Acceptable Overall Risk Factor than only Lighting Protection Required
  • Here Calculated Overall Risk Factor is 0.000110127 > Max Acceptable Overall Risk Factor is 00000001
  • Lightning Protection is Required

 No of Down Conductor

  • Down Conductors As per Base Area of Structure (s) =1+(Ab-100)/300
  • Down Conductors As per Base Area of Structure (s) =1+(1680-100)/300
  • Down Conductors As per Base Area of Structure (s) =6 No’s
  • Down Conductors As per Perimeter of Structure (t)= P/30
  • Down Conductors As per Perimeter of Structure (t)= 176/30
  • Down Conductors As per Perimeter of Structure (t)= 6 No’s
  • Minimum No of Down Conductor is 6 No’s


  • Lightning Protection is Required
  • Down Conductors As per Base Area of Structure (s) =6 No’s
  • Down Conductors As per Perimeter of Structure (t)= 6 No’s
  • Minimum No of Down Conductor is 6 No’s

Thumb Rule-13

Approximate Fuel Consumption for Diesel Generator Set

Generator Size (Kva) @0.8 PF 1/4 Load (Liter/Hr) 1/2 Load (Liter/Hr) 3/4 Load (Liter/Hr) Full Load (Liter/Hr)
25 2.27 3.41 4.92 6.06
38 4.92 6.82 9.09 10.98
50 6.06 8.71 12.12 15.15
75 6.82 10.98 14.39 18.18
94 9.09 12.88 17.42 23.11
125 9.85 15.53 21.97 28.03
156 11.74 18.94 26.89 34.47
169 12.50 20.45 28.79 37.12
188 13.64 22.35 31.82 41.29
219 15.53 25.76 36.74 48.11
250 17.80 29.17 41.67 54.55
288 20.08 33.33 47.35 62.88
313 21.59 35.98 51.52 68.18
375 25.76 42.80 60.98 81.44
438 29.92 49.62 70.83 95.08
500 33.71 56.44 80.68 108.33
625 41.67 70.08 100.00 135.23
750 50.00 83.33 119.32 162.12
938 61.74 103.79 148.86 202.27
1250 81.82 137.88 197.35 269.32
1563 101.89 171.59 246.21 336.36
1875 121.97 205.68 294.70 403.41
2188 142.05 239.39 343.56 470.45
2500 162.12 273.48 392.05 537.50
2813 182.20 307.20 440.91 604.55

Approximate Current (Amp) Rating of Diesel Generator Set @ 0.8 PF

KVA kW 220V 240V 400V 440V 450V 480V 600V 2400V 3300V
8 6.3 16.5 15.2 9.1 8.3 8.1 7.6 6.1    
9.4 7.5 24.7 22.6 13.6 12.3 12 11.3 9.1    
12.5 10 33 30.1 18.2 16.6 16.2 15.1 12    
18.7 15 49.5 45 27.3 24.9 24.4 22.5 18    
25 20 66 60.2 36.4 33.2 30.1 24 6 4.4 3.5
31.3 25 82.5 75.5 45.5 41.5 40.5 37.8 30 7.5 5.5
37.5 30 99 90.3 54.6 49.8 48.7 45.2 36 9.1 6.6
50 40 132 120 73 66.5 65 60 48 12.1 8.8
62.5 50 165 152 91 83 81 76 61 15.1 10.9
75 60 198 181 109 99.6 97.5 91 72 18.1 13.1
93.8 75 247 226 136 123 120 113 90 22.6 16.4
100 80 264 240 146 133 130 120 96 21.1 17.6
125 100 330 301 182 166 162 150 120 30 21.8
156 125 413 375 228 208 204 188 150 38 27.3
187 150 495 450 273 249 244 225 180 45 33
219 175 577 527 318 289 283 264 211 53 38
250 200 660 601 364 332 324 301 241 60 44
312 250 825 751 455 415 405 376 300 75 55
375 300 990 903 546 498 487 451 361 90 66
438 350 1155 1053 637 581 568 527 422 105 77
500 400 1320 1203 730 665 650 602 481 120 88
625 500 1650 1504 910 830 810 752 602 150 109
750 600 1980 1803 1090 996 975 902 721 180 131
875 700 2310 2104 1274 1162 1136 1052 842 210 153
1000 800 2640 2405 1460 1330 1300 1203 962 241 176
1125 900 2970 2709 1640 1495 1460 1354 1082 271 197
1250 1000 3300 3009 1820 1660 1620 1504 1202 301 218
1563 1250 4130 3765 2280 2080 2040 1885 1503 376 273
1875 1500 4950 4520 2730 2490 2440 2260 1805 452 327
2188 1750   5280 3180 2890 2830 2640 2106 528 380
2500 2000   6020 3640 3320 3240 3015 2405 602 436
2812 2250   6780 4095 3735 3645 3400 2710 678 491

Calculate Cable Voltage Drop for Street Light Pole

Example: Calculate Voltage drop of Cable for Street Light Pole. System Voltage is 230V (P-N), Power Factor=0.75. Allowable Voltage Drop = 4% .The Detail of Pole & cable are

Pole Detail:

  • Section feeder Pillar is 50 meter away from Pole-1
  • Distance between each Pole is 50 Meter Distance
  • Luminar of Each Pole Fitting = 2 No’s
  • Luminar Watt =250 Watt

Cable Detail:

  • Size of Cable= 4CX10
  • First Pole is connected in R Phase Next Pole is connected in Y Phase Than Next Pole is connected in B Phase. Next Pole is connected again R Phase.
  • Resistance of Cable=3.7 Ω/Km
  • Reactant of Cable=0.1 Ω/Km



Load of Each Pole

  • Load of Each Pole = (Watt of Each Luminar X No of Luminar ) / Volt X P.F
  • Load of Each Pole = (250X2) /(230X0.75)
  • Load of Each Pole = 2.9 Amp

For Pole Pole-1:

  • Pole Connected on “R” Phase
  • Total Distance of Pole for “R” Phase =50 Meter ,
  • % Voltage drop of Cable= (Current X (Rcosᴓ + JSinnᴓ) X Distance ) / (Volt X No of Cable X 1000)
  • % Voltage drop of Cable= (2.9x(3.7×0.75+0.1×0.66)X50 / (230x1x1000)
  • % Voltage drop of Cable= 0.18% ———————————(1)

For Pole Pole-2:

  • Pole Connected on “Y” Phase
  • Total Distance of Pole for “Y” Phase =50+50=100 Meter ,
  • % Voltage drop of Cable= (Current X (Rcosᴓ + JSinnᴓ) X Distance ) / (Volt X No of Cable X 1000)
  • % Voltage drop of Cable= (2.9x(3.7×0.75+0.1×0.66)X100 / (230x1x1000)
  • % Voltage drop of Cable= 0.36% ———————————(2)

For Pole Pole-3:

  • Pole Connected on “B” Phase
  • Total Distance of Pole for “B” Phase =50+50+50=150 Meter ,
  • % Voltage drop of Cable= (Current X (Rcosᴓ + JSinnᴓ) X Distance ) / (Volt X No of Cable X 1000)
  • % Voltage drop of Cable= (2.9x(3.7×0.75+0.1×0.66)X150 / (230x1x1000)
  • % Voltage drop of Cable= 0.54% ———————————(3)

For Pole Pole-4:

  • Pole Connected on “R” Phase
  • Total Distance of Pole for “R” Phase =150+50=200 Meter ,
  • % Voltage drop of Cable= (Current X (Rcosᴓ + JSinnᴓ) X Distance ) / (Volt X No of Cable X 1000)
  • % Voltage drop of Cable= (2.9x(3.7×0.75+0.1×0.66)X200 / (230x1x1000)
  • % Voltage drop of Cable= 0.72% ———————————(4)

For Pole Pole-5:

  • Pole Connected on “Y” Phase
  • Total Distance of Pole for “Y” Phase =200+50=250 Meter ,
  • % Voltage drop of Cable= (Current X (Rcosᴓ + JSinnᴓ) X Distance ) / (Volt X No of Cable X 1000)
  • % Voltage drop of Cable= (2.9x(3.7×0.75+0.1×0.66)X250 / (230x1x1000)
  • % Voltage drop of Cable= 0.9% ———————————(5)

For Pole Pole-6:

  • Pole Connected on “B” Phase
  • Total Distance of Pole for “B” Phase =250+50=300 Meter ,
  • % Voltage drop of Cable= (Current X (Rcosᴓ + JSinnᴓ) X Distance ) / (Volt X No of Cable X 1000)
  • % Voltage drop of Cable= (2.9x(3.7×0.75+0.1×0.66)X300 / (230x1x1000)
  • % Voltage drop of Cable= 1.07% ———————————(6)

For Pole Pole-7:

  • Pole Connected on “R” Phase
  • Total Distance of Pole for “R” Phase =300+50=350 Meter ,
  • % Voltage drop of Cable= (Current X (Rcosᴓ + JSinnᴓ) X Distance ) / (Volt X No of Cable X 1000)
  • % Voltage drop of Cable= (2.9x(3.7×0.75+0.1×0.66)X350 / (230x1x1000)
  • % Voltage drop of Cable= 1.25% ———————————(7)

For Pole Pole-8:

  • Pole Connected on “Y” Phase
  • Total Distance of Pole for “Y” Phase =350+50=400 Meter ,
  • % Voltage drop of Cable= (Current X (Rcosᴓ + JSinnᴓ) X Distance ) / (Volt X No of Cable X 1000)
  • % Voltage drop of Cable= (2.9x(3.7×0.75+0.1×0.66)X400 / (230x1x1000)
  • % Voltage drop of Cable= 1.43% ———————————(8)

For Pole Pole-9:

  • Pole Connected on “B” Phase
  • Total Distance of Pole for “B” Phase =400+50=450 Meter ,
  • % Voltage drop of Cable= (Current X (Rcosᴓ + JSinnᴓ) X Distance ) / (Volt X No of Cable X 1000)
  • % Voltage drop of Cable= (2.9x(3.7×0.75+0.1×0.66)X450 / (230x1x1000)
  • % Voltage drop of Cable= 1.61% ———————————(9)

Total Voltage Drop:

  • Voltage Drop in “R” Phase = 0.18+0.72+1.25 =2.15 %
  • Voltage Drop in “Y” Phase =0.36+0.90+1.43 =2.69 %
  • Voltage Drop in “B” Phase =0.54+1.07+1.61 =3.22 %
  • % Voltage drop in each Phase is Max 3.22% Which is less than 4%


Phase No of Pole Load (Amp) Voltage Drop
R 3 9 2.15 %
Y 3 9 2.69 %
B 3 9 3.22 %
Total 9 9 2.55 %

Cable Voltage Drop for Different Size of Cables

ScreenHunter_01 Feb. 04 17.50

  • Calculate Voltage of Cable having Different Size
  • Calculate Starting Current
  • Calculate Running Current
  • Calculate Starting Voltage Drop
  • Calculate Running Voltage Drop

                          FREE DOWNLOAD


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