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Home / Technical Articles / An example how to calculate voltage drop and size of electrical cable

Input information

Electrical details:

Electrical load of 80KW, distance between source and load is 200 meters, system voltage 415V three phase, power factor is 0.8, permissible voltage drop is  5%, demand factor is 1.

Cable laying detail:

Cable is directed buried in ground in trench at the depth of 1 meter. Ground temperature is approximate 35 Deg. Number of cable per trench is 1. Number of run of cable is 1 run.

An example how to calculate voltage drop and size of electrical cable
An example how to calculate voltage drop and size of electrical cable (photo credit:

Soil details:

Thermal resistivity of soil is not known. Nature of soil is damp soil.

Ok, let’s dive into calculations…

  • Consumed Load = Total Load · Demand Factor:
    Consumed Load in KW = 80 · 1 = 80 KW
  • Consumed Load in KVA = KW/P.F.:
    Consumed Load in KVA = 80/0.8 = 100 KVA
  • Full Load Current = (KVA · 1000) / (1.732 · Voltage):
    Full Load Current = (100 · 1000) / (1.732 · 415) = 139 Amp.

Calculating Correction Factor of Cable from following data:

Temperature Correction Factor (K1) When Cable is in the Air

Temperature Correction Factor in Air: K1
Ambient TemperatureInsulation

Ground Temperature Correction Factor (K2)

Ground Temperature Correction Factor: K2
Ground TemperatureInsulation

Thermal Resistance Correction Factor (K4) for Soil (When Thermal Resistance of Soil is known)

Soil Thermal Resistivity: 2.5 KM/W

Soil Correction Factor (K4) of Soil (When Thermal Resistance of Soil is not known)

Nature of SoilK3
Very Wet Soil1.21
Wet Soil1.13
Damp Soil1.05
Dry Soil1
Very Dry Soil0.86

Cable Depth Correction Factor (K5)

Laying Depth (Meter)Rating Factor

Cable Distance correction Factor (K6)

No of CircuitNilCable diameter0.125m0.25m0.5m

Cable Grouping Factor (No of Tray Factor) (K7)

No of Cable/Tray123468

According to above detail correction factors:

– Ground temperature correction factor (K2) = 0.89
Soil correction factor (K4) = 1.05
– Cable depth correction factor (K5) = 1.0
– Cable distance correction factor (K6) = 1.0

Total derating factor = k1 · k2 · k3 · K4 · K5 · K6 · K7

– Total derating factor = 0.93

Selection of Cable

For selection of proper cable following conditions should be satisfied:

  1. Cable derating amp should be higher than full load current of load.
  2. Cable voltage drop should be less than defined voltage drop.
  3. No. of cable runs  (Full load current / Cable derating current).
  4. Cable short circuit capacity should be higher than system  short circuit capacity at that point.

Selection of cable – Case #1

Let’s select 3.5 core 70 cable for single run.

  • Current capacity of 70 cable is: 170 Amp,
    Resistance = 0.57 Ω/Km and
    Reactance = 0.077 mho/Km
  • Total derating current of 70 cable = 170 · 0.93 = 159 Amp.
  • Voltage Drop of Cable =
    (1.732 · Current · (RcosǾ + jsinǾ) · Cable length · 100) / (Line voltage · No of run · 1000) =
    (1.732 · 139 · (0.57 · 0.8 + 0.077 · 0.6) · 200 · 100) / (415 · 1 · 1000) = 5.8%

Voltage drop of cable = 5.8%

Here voltage drop for 70 Cable (5.8 %) is higher than define voltage drop (5%) so either select higher size of cable or increase no of cable runs.

If we select 2 runs, than voltage drop is 2.8% which is within limit (5%) but to use 2 runs of cable of 70 cable is not economical, so it’s necessary to use next higher size of cable.

Selection of cable – Case #2

Let’s select 3.5 core 95 cable for single run, short circuit capacity = 8.2 KA.

  • Current capacity of 95 cable is 200 Amp,
    Resistance = 0.41 Ω/Km and
    Reactance = 0.074 mho/Km
  • Total derating current of 70 Cable = 200 · 0.93 = 187 Amp.
  • Voltage drop of cable =
    (1.732 · 139 · (0.41 · 0.8 + 0.074 · 0.6) · 200 · 100) / (415 · 1 · 1000) = 2.2%

To decide 95 cable, cable selection condition should be checked.

  1. Cable derating Amp (187 Amp) is higher than full load current of load (139 Amp) = O.K
  2. Cable voltage Drop (2.2%) is less than defined voltage drop (5%) = O.K
  3. Number of cable runs (1) ≥ (139A / 187A = 0.78) = O.K
  4. Cable short circuit capacity (8.2KA) is higher than system short circuit capacity at that point (6.0KA) = O.K

95 cable satisfied all three condition, so it is advisable to use 3.5 Core 95 cable.

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Jignesh Parmar

Jignesh Parmar has completed M.Tech (Power System Control), B.E (Electrical). He is member of Institution of Engineers (MIE), India. He has more than 20 years experience in transmission & distribution-energy theft detection and maintenance electrical projects.


  1. Hardeep
    Sep 15, 2023

    You explain it very well, really informative. But please consider cable type ( aluminium or copper)

  2. Jeremy Goodman
    Aug 28, 2023

    I am trying to find out how to calculate the voltage drop of 3 phase AC in aluminum 750kcmil single conductors in cable tray over 850ft to support a max load of 3000A. What is the voltage drop formula for cable larger than 4/0? What NEC table do use to get the resistance value of 3 phase power through aluminum 750kcmil wire on a cable tray?

  3. Tejas Varma
    Jul 25, 2023


    Just a question, if Resistance and Reactance values are taken in per kilometer form then why cable length is considered in meters instead of kilometers ?

    Every value must be in similar units be it meters or kilometers!

  4. Rajganesh
    Jun 16, 2023

    How to calculate short circuit capacity of the cable?

  5. Mohamed Faisal
    May 20, 2023

    In cable Sizing for the voltage drop calculation what is the formula for sin pi value . How will you find the sind pi value

  6. Grace Yu
    May 08, 2023

    3phase 400Vac, 65KW and 65 Length
    Note: Operating condition: -10°C ~ 40°C, up to 95% humidity, altitude at 1500ft above sea level
    With the kW rating and cable length available, fill in the cable size above; Power Factor 0.75, Maximum Voltage Drop <3%

  7. Grace Yu
    May 08, 2023

    Motors are sized at 1.5kW (3Ø, 400Vac, F.L.A. 3.5Amp) with mechanical brake (1Ø, 400Vac, F.L.A. 0.1Amp) for all 3 motors. All these motors are required to control speed. Design a motor control panel (MCP) for the
    Sketch MCP Single line diagram with workout for breaker sizing.
    Sketch MCP wiring schematic diagram. Please also consider for Safety. Free to use the familiar devices except the following Devices.
    VFD: Schneider ATV310
    PLC: Allen Bradley CompactLogix 5370 L3

  8. kaushal pandey
    Oct 09, 2022

    sir pls help me how to find cable current capacity alluminium and copper.

    • Deepak parmar
      Feb 25, 2023

      I am working amrit papers mill but no any experience because I am fresher so can you help me about my choice and again future plan in involve my knowledge..plz tell me som imformation..

  9. Govind Waghmare
    Sep 26, 2022

    How we can calculate voltage drop for distributed network :
    example :
    Incoming from feeder pillar to meter room panel to No of connected load.

  10. Sanjay Gupta
    Aug 25, 2022

    Why voltage drop 5% and 15% is permissible. Please reply.

  11. Sanjay Gupta
    Jul 20, 2022

    How to calculate cable sizing and voltage drop starting and running condition ( Starting Permissible voltage drop is 15 %. and Running Permissible voltage drop is 5 %.)

    • Sanjay Gupta
      Jul 20, 2022

      Plz reply

  12. Dilip Siju
    Apr 08, 2022

    What will be change in voltage drop calculation if we’re using cable for single phase applications?

  13. Oyamendan ENAHOLO Philip
    Feb 21, 2022

    Sir, i want to hook up a gas Waukesha generator that is 400hp/298kw. Now from the point of generator to the MCC Room is 30meters. Is a 60hz/460volts alternator. Pls, what size of cable can i use for single and double run. Thanks.

  14. Sanjay Nagarkar
    Feb 14, 2022

    If i am using ac supply 300 sq mm cable for 290 mtrs 2 run what will be voltage drop and is there any power loss due to cable length ? is it necessary to add one more 300 sq mm cable of 290 mtr to compensate power loss ? i am ref this to Solar plant of 990 KWP.outpot of solar panel to connect to my DB.

  15. Sanjay Nagarkar
    Feb 14, 2022

    I would love to join your group to improve my knowledge.

  16. awais
    Feb 09, 2022

    suppose we are going to size a cable for motor. my question is that why we use efficiency in cable sizing formulae for motor while efficiency already encountered during selection of motor?

  17. Eric Perry
    Jan 18, 2022

    I’m developing a multifamily subdivision. (12 buildings ) consists of 18 units each buildind.
    I’m planning on running unground eletric, 8 feet deep.

    Each build will have a inside transformation. 1,100kva. Each building unit will have the strength of 60,000 volts.

    I need to know what size wire I use to jump style of the transformers to each build from one power source of the main supply. So basically a line that can support 13,000 kva. Can someone help?

    [email protected]

  18. Alejandro
    Jan 16, 2022

    In which standard can I find these tables for the correction factors?

  19. Zahirul islam
    Dec 07, 2021

    Different topics on improvement of electric distribution system and related calculations etc.

  20. Benjamin Rich
    Oct 26, 2021

    A 2 core cable supplies current to a 240v single phase load of 18kw at 0.78 power factor. The cable is 40m long and each conductor has a cross-sectional area of 35mm.calculate the voltage drops in the cable at the load,ignoring the reactance of the cable?

  21. hema
    Oct 22, 2021

    Voltage drop of cable =
    (1.732 · 139 · (0.41 · 0.8 + 0.074 · 0.6) · 200 · 100) / (415 · 1 · 1000) = 2.2%

    answer not coming, explain pl.

    • Swarup
      Oct 30, 2021

      Yeah, voltage drop Calculation for 3.5C x 95 mm² is incorrect. it should be 4.3% instead of 2.2 %

  22. Avishek Banerjee
    Sep 25, 2021

    This information is fantastic.


  23. S K MANDAL
    Sep 03, 2021

    Allowable voltage drop : 5%, Cable Length: 1300M, Motor power: 110KW. cable to be laid on tray in air
    Cable size?

  24. Hennah S. Kamara
    Sep 03, 2021

    From the above calculations of Full Load current, I still have a doubt.
    Why did we ignored the PF in getting our full Load current?

    KVA/ 1.732*415 =amp

    Amp =KVA/1.732*415*0.8

    • Marifat Majid
      Nov 02, 2021

      KVA/1.732*VL =amp , if we include PF then it wont be kVA which is Apparent power, but Real Power kW.
      so we will have, kW/1.732*VL*PF = amp
      hope this clears the confusion.

    • Akshay
      Nov 12, 2021

      Amp = KVA/(1.732*415) or
      Amp = KW/(1.732*415*0.8)

      Hope you understand the difference.

  25. Afnitha
    Sep 01, 2021

    How we can calculate number of cables that can accommodate in a cable tray ?

    Jul 27, 2021

    how to calculate cable sizes when the total load is 18 kw but it is divided into 6 towers each at a distance of 1 km and each tower has a load of 3 kw ,with 3 towers on one side and 3 towers on the other side , and placing one feeder pillar between them (i.e . 3 towers on one side then feeder pillar and then 3 towers on other side), which will feed them supply ,this feeder will given main supply from LT PANEL placed at a distance of 700 mtrs . please do tell . this is the problem i am facing .

  27. Dirshe
    Jul 16, 2021 3.5 core cable which standard is this?

  28. Adegoke Adeyemi Adewara
    Jul 07, 2021

    I love this platform. Looking forward to learning more from you genius.

    Jul 02, 2021


  30. Durga
    May 04, 2021

    How to identify the value for R and j
    For 95 sq mm R=0.41 · 0.8 + j=0.074 · 0.6
    Where as
    For 70 sq mm R=0.57 · 0.8 + j=0.077 · 0.6)

    • Nuwan
      Jun 03, 2021

      It’s tabulated value. BS 7671:2018

    • SURAJ
      Jul 06, 2021


      • Suraj yadav
        Jul 19, 2021

        Why I couldn’t find current ratings chart

  31. siva
    Apr 26, 2021

    (1.732 · 139 · (0.57 · 0.8 + 0.077 · 0.6) · 200 · 100) / (415 · 1 · 1000) = 5.8%

    sir from above how we got 139

    • Shivaram
      Apr 29, 2021

      Consumed Load = Total Load · Demand Factor:
      Consumed Load in KW = 80 · 1 = 80 KW
      Consumed Load in KVA = KW/P.F.:
      Consumed Load in KVA = 80/0.8 = 100 KVA
      Full Load Current = (KVA · 1000) / (1.732 · Voltage):
      Full Load Current = (100 · 1000) / (1.732 · 415) = 139 Amp.

      • Suraj yadav
        Jul 19, 2021

        I need DC motor current rating chart

      • zeeshan raza
        Jul 26, 2021

        Instead of this, we can use a simple formula for 3 core cables – total connected load x 1.74 = load current

  32. Owais
    Apr 20, 2021

    Sir, what is the figure 1.732?

    Apr 19, 2021

    Thanks for sharing.

    Mar 24, 2021

    Sir, what will be the cable derated ampacity incase if i have 3 runs of 1C cable with base ampacity 170amps & cable derating 0.8. do i have to times with 1.732, say 170×0.8×1.732=235.5A. please guide.

  35. Devdutt Vin
    Mar 09, 2021

    Sir, please let us know from which standard (IEC / BS / IS) you have taken the cable ratings.

  36. TJ Khawaja
    Feb 18, 2021

    (1.732 · 139 · (0.41 · 0.8 + 0.074 · 0.6) · 200 · 100) / (415 · 1 · 1000) = 2.2%
    the above calculation does not give 2.2% it gives 4.3% please check again. If you use two runs then it will be 2.2%

  37. Parikshit Ningavale
    Jan 31, 2021

    Dear sir, how did you take system short circuit capacity as 6kA?

    Jan 26, 2021


  39. kome makoge elvise
    Jan 21, 2021

    Good day,
    Please what is your reference for selecting resistance and reactance values

  40. Yogendra Singh Singhvi
    Oct 09, 2020

    How we got 139 amperes after getting 170*0.93=158.10, calculation for derated current?
    Some step is missing.

  41. val
    Aug 18, 2020

    Sir. can you please give an idea on how did you get the value of .8 and .6. can you show to me the computation

  42. Waqas
    Aug 09, 2020

    i need clarification how sin Value is 0.6? any calculation behind it?

      Aug 11, 2020

      yes there is calculation ,with formula that is sinǾ = SQRT(1-( cosǾ * cosǾ))

    • irfan
      Mar 10, 2021

      cos(fi)= o.8
      cos inv. of 0.8 is 36.86
      then sin of 36.86 is 0.599986 i.e approx 0.6

  43. Mizan Al Aqaid
    Jul 21, 2020

    What the distance between load and supply ? What is the voltage value ? Pf ? And more. Are you serious about your question?

    • Dipankar Rai
      Jul 28, 2020

      He has considered everything 200m length, 415 V voltage, Pf for converting Kw to KVA.
      So what are you asking????

  44. Mundiya Mulozi
    Jul 20, 2020

    how do i calculate the size of the cable, given the power and voltage, taking installation methods and correction factors into account. e.g. an electrical load is 80KW located at a distance of 200m from supply, voltage is 415V three phase, power is 0.8, permissible voltage drop is 5% and demand factor is 1.

  45. Harvinder Paul Singh
    Jun 19, 2020

    Sir pl supply a cable size calculator EXEL Sheet.

  46. solomon
    May 02, 2020

    generate 1250 kva and transformer 1200 kva the power haws 1600 A bracer what cable size

  47. Sheik
    Apr 24, 2020

    Thank u so much sir, such a wonderful messages.And please sir I need to know about how prepared load calculation and schedule?

    • Mizan Al Aqaid
      Jul 21, 2020

      You must know about your load in system sir, classification about motor and feeder loads, service unit (continuous, intermittent, spare), and then calculation consumed load, demand load, peak load. After that, you can sizing trafo rating, generator rating, Ishort circuit, cable sizing, and more.

  48. teja
    Mar 04, 2020

    Hello sir, is there any formula to calculate the spare load in a electrical panel from the amperage values of branch circuit breakers.

  49. Kalpesh
    Feb 07, 2020

    Hello sir, are this factors applicable for UNINYVIN cables also.

  50. Uvaosudheen m
    Feb 02, 2020

    Hlo sir,. I understood all these calculations and I studied well.
    But now I need the table which have the datas of cable like current carrying capacity, etc. Plz share iny email
    . I hope your earliest reply. Thanku

  51. salahodeen
    Dec 31, 2019

    Control cable for high voltage s/s laid in a cable tray in a trench, is it a must to be armored or not, and what does IEC said in this issue.

    thanks a lot

  52. Rahul Kumar Dubey
    Dec 24, 2019

    415V, 10kw is Light Power load and if we calculate amp so it will be 18amp. Then why we select 10 or 16asqmm cu or Alar cable, but this cable current capacity is 3 times greater to load. Please Explain

    Nov 26, 2019

    sir kindly reply me how I simply calculate, how many amp.current taken by any ht or lt cable

  54. Amjad Ali
    Oct 27, 2019

    Dear Sir
    Please tell how to calculate the size of 11 kV distribution overhead aluminum conductor (ACSR) for particular load and distance.

  55. satu
    Oct 01, 2019

    Hello Sir, Kindly help…I’m going to install lightning fixture for tunnel with a total lenght of 7500meters. the lights consist of 2x36watts a distance of every 10meters.
    Circuit breaker – ?
    Cable size – ?
    Transformer type to be install about 4kms. – ?

  56. Mohamed Gaber
    Sep 24, 2019

    Dear Mr. Jignesh Parmar;

    You used The demand factor for the calculation of consumed load but as I checked all other sources and calculation programs no use for the demand factor of loads , Kindly explain and provide your source for this formula

    Sep 12, 2019

    how to take the de-rating value for K1,K2,K3 K4,K5

  58. Enkali jafet Nyanyukweni
    Sep 10, 2019

    Hi, help me please: A single phase 10kw motor is connected 50m from the distribution board by an underground armoured copper cable. USE different cable sizes to determine the correct cable suitable for this motor starting with smallest cable for the load and calculate the correct cable that can be used? Calculate the % volt drop for the correct cable?

  59. Patience
    May 30, 2019

    I want to supply a pump 8m away from the point of supply. The cable will be through a cable tray. The pump specs are:
    Rated Voltage: 230 Vac single phase
    Rated Power: 0.25kW
    Load Current: 1.9 A
    Locked Rotor Current:4.8A

    How do you calculate the size of the circuit breaker (in Amps) and cable (in mm2).

  60. siddharth jain
    May 17, 2019

    Hi All,
    How to select the value of cosǾ & sinǾ in the formula.
    Voltage Drop of Cable= (1.732x Current x (RcosǾ+jsinǾ) x Cable Lengthx100) / (Line Voltage x No of Runx1000)
    Can anyone help me in this please?

    • shilpa
      Jul 30, 2019

      While calculating the voltage drop, cosǾ = starting p.f.(0.2), which is constant.
      sinǾ = SQRT(1-( cosǾ * cosǾ)).
      Example ; cosǾ=0.2 , then sinǾ = SQRT(1-( 0.2 * 0.2)) =0.979

    • shilpa
      Jul 30, 2019

      Voltage Drop of cable at Full load = (1.732*current *((resistance*cosǾ)+(reactance *sinǾ)) * cable length * 100) / (line voltage * No.of runs * 1000)

      Voltage Drop of cable at transient = (1.732*current *((resistance*cosΦst)+(reactance *sinǾst)) * cable length * 100) / (line voltage * No.of runs * 1000)

      where, cosΦst = 0.2
      sinǾst = SQRT (1-(0.2*0.2))

    • srinivasyadav
      Aug 06, 2019

      cospi is power factor from there u can find sinpi using inverse cos formula

    • Premdas
      Dec 08, 2019

      Ǿ depends on the load.

  61. Prem Hari Shama
    May 04, 2019

    Dear sir if my cable 500 metar how to celculet current. With formula.
    3ph aluminium 150mm 100metar lenth 215A. if i am increase cable lenth 100 to 500metar how many amp take current of al cable

    Apr 24, 2019

    Dear sir,
    Sir I am working in Bahrain, I am an Electrical supervisor.Sir can you explain to me how to calculate the cable size as per the total load

  63. Kamal
    Apr 20, 2019

    2.2% voltage drop calculated in this article for 95 cable is wrong. Please recalculate & correct it. It comes out to be 4.32% & not 2.2%.


      Aug 30, 2019

      The voltage drop for 90 sqmm cabe 2.2% is wrong it should be 4.3 %

    • lokeshkumar
      Sep 03, 2019

      you are correct i got 4.3 too

  64. Ramsha Nawal Alvi
    Apr 08, 2019

    Dear Sir,

    Thanks for the beneficial information. I have no electrical background,i am a chemical engineer and have a keen interest to understand about the cable sizing criteria but have needed some leads from your side which would be very helpful for me. Sir regarding your work explained above, i want some clarifications from you on the given below listed points:
    1 On what basis (assumptions) you have let the size of cable ” 3.5 core 70 sq mm” & “3.5 core 95 sq mm”. please explain.
    2 From where you get the value of current capacities of 170 Amp & 200 Amp?
    3 From where you get the value of resistance & reactances?
    4 From where you get the value of theeta ?
    5 From where you get the value of short circuit capacities of 8.2KA & 6.0KA?
    Waiting for your kind response sir.
    Thank you.

  65. hang chetha
    Mar 22, 2019

    Can you tell me why you multiple Resistance and Reactance to 0.8 and 0.6?


    • Himanshu Sachan
      Jun 25, 2019

      Cos$ is equal to the power factor and value of power factor is 0.8 from here we can get the vale of theta and then we can calculate Sin$ which is equal to 0.6

  66. NL Chauhan
    Mar 19, 2019

    I have one cable of 3 1/2 core .Actual size/rating in sqmm is not known to me.Diameter & perimeter of the cable is known.Please specify how to calculate the size in sqmm. Similarly if the cable is single core than also how to calculate the size if these two parameters are known

  67. Hardeepsingh
    Mar 11, 2019

    Dear Sir,
    In above calculation you have consider 200 mtr cable length. Please inform, it is 200 mtr distance between source terminal and Load terminal or you consider 100 mtr line cable and 100 mtr nutral cable as 200 mtr total length.

  68. Kamal Naser
    Feb 16, 2019

    I need the excel calculation sheets and correction factors

  69. kaushal pandey
    Feb 06, 2019

    sir i want your excel sheet then pls send me

  70. Satish Deore
    Feb 05, 2019

    Respect sir. I guide cable size 1200 ft lengthfrom 63 transformer.15 hp 5 stage submersible motor .

  71. Ali Allahverdizadeh
    Jan 15, 2019

    Would you please let me know if there is any de-rating factor which should be applied for the feeder cables with more than one cable in each phase to compensate current unbalance in each individual conductor. Please mention any standard for this.
    I have seen in some cable sizing document that we should apply 1.15 factor for sizing of cables for feeders with more than one cable in each phase, but couldn’t find any reference standard for that.
    Please share your knowledge in this case with me and email it to [email protected].

  72. PAUL
    Nov 15, 2018


      Nov 20, 2018

      copper cable of 3core 150sqmm 2runs cable.

    • Naval Tayde
      Jan 29, 2019

      4Cx240mm2 XLPE + 1Cx120 mm2 will be sufficient to feed 630Amp.

  73. rasty
    Oct 21, 2018

    could you attach cable capacity table and resistance/Km it will be so helpful

  74. Md. Samsul Arefin
    Aug 07, 2018

    How can we calculate the Reactance of a 3.5 core 95 cable . Here you have mentioned the reactance 0.074 mho/Km. Can you explain the formula to calculate reactance for any core or size cables ?
    Thank you.

  75. Paresh
    Jul 27, 2018

    I wanted to calculate underground armourered cable size in aluminium, our society/colony is having 3 lanes.

    How do i calculate the cable size depending on Amper rating.

    Current i am calculating:

    Month unit per home – assumed 200 Kwh , in KW 20 , i.e for per day approx 1 KW. total KW for 40 Homes , 40 KW. for single phase voltage , 40000w / 230 = 173.91 amper & for 3 phase voltage 40000W/440 = 90.9 ampere.
    do i need to consider the voltage drop in %ge & add in the ampere rating.

    Please confirm correct calculation to choose proper underground cable, its urgent.

  76. Joseph Gyebuni
    May 12, 2018

    please I need help to tackle a voltage drop issue in my company. We have installed a steam turbine generator of 1MW and voltage of 400V. We use about 40% of the capacity to feed our 30tons/hr palm oil mill and we have extended the power to our residencies which is about 1Km from the generation point. At the distribution point for the residencies we have a voltage of 330-345V. we used 120 aluminium. we have also used 3 changeovers in the line. now some of our fridges and metal halides bulbs are not working properly. what can we do to improve the voltage? some suggestion came that we should installed a capacity bank at the residents distribution point and another suggested that we should used transformers to step up at the generation site and step down at the residents distribution point. please I need help urgently. I am an electrical engineer under training. thank you very much for helping.

    • ROY
      May 25, 2019

      Hi Joseph
      I am just an electrician.not a part of EEP..I see that this was a post from a year ago,so I hope you have by now solved your problem..To me your cable,without doing the calculations sounds to be undersized..Copper would probably have been a better choice than aluminium.I don’t think transformers to step up and down would be the answer as I believe the criteria for the cables burying depth and protection would be different for MV than LV and also the cost of the 2 transformers could be prohibitive..presumably your voltage live to neutral is just 190volts …….I think at the generator the voltage could probably be increased to 440 volts without too mush of a cost..which would give you a slight increase at the residence end…..How many residences are supplied by this cable?…….Would it be possible that you could convert to single phase …doubling up on 2 pairs of cables (if there is a distributed neutral),though that might cause quite an imbalance on phases back at the factory…Even a temporary change to confirm the volt drop is acceptable.then you could run in another KM of similar sized cable to double up.

    • S k pattnaik
      May 27, 2020

      High drop in voltage is because of 1km cable length. Lay 240sqmm 2 runs to get with in 5% drop.

  77. Nkosinathi
    May 08, 2018

    Please help I have an assignment same as this format but given a single phase , please help me I need to find a diameter of the cable so I can find d area…to find voltage drop in the cable …and I’m stuck how can I choose ?
    “You have been hired by the UMLAZI Construction Company to design, Electrical load
    of 80KW, distance between source and load is 200 meters, system voltage 230V single
    phase, power factor is 0.8, permissible voltage drop is 10% according to South African
    Bureau of Standards (SABS) under SANS 10142 wiring code and demand factor is 1. Cable
    is directed buried in ground in trench at the depth of 1 meter. Ground temperature is
    approximate 35 Deg. Number of cable per trench is 1. Number of run of cable is 1 run. The
    company will be choosing one of the model designs from this class and it is your job to sell
    them your best design. You are expected to work in the group of TEN on your design, and
    follow a strict timeline. Do the selection of proper cable following Specifications:

    • shani
      Jun 20, 2018

      i can help yu… i will give yu a excel sheet which will automatic calculate the cable voltage drop nd yu can choose a correct daimater cable size easily. for further info yu can contact me on my email adress.

      • Tufan Halder
        Sep 28, 2018

        I need your Excel sheet. My mail id [email protected] and contct no.9682156495. Please contact with me.

      • Twana
        Oct 08, 2018

        Dear Shani,
        Could you be able to send the excel sheet which will automatically calculate the cable voltage drop to my email too? this is my email:
        [email protected]
        Thank you.

      • hang chetha
        Mar 22, 2019

        can I have that excel sheet? will thank you so much
        my mail is [email protected]

        May 14, 2020

        Dear Shani

        Pl. share me excel sheet , which will automatic calculate the cable voltage drop and we can choose a correct Daimler cable size easily.
        my mail id is
        [email protected]

        Jan 04, 2021

        Sir Plez send me your excel Sheet For Calculating Cable Size and Voltage Drop

  78. Hozan
    Mar 27, 2018

    Good explaintion, but is it as per IEC, if so please give us the source of these tables, K1,2,3,4,5,6

  79. Muhammad Asad Basit
    Feb 15, 2018

    Dear Sir,
    you mention system short circuit current capacity is 6KA. Please tell me how to find the system short circuit current capacity.


  80. s.m shahiduzzaman
    Jan 08, 2017

    sir.I want to calculate the amount of ampere on the respect of cables dia meter or rm or mm.if you please help me.

  81. santhakumar
    Jan 04, 2017

    I appreciate your service with my whole heart. I am also an Electrical Engineer. I have one small doubt on this regarding the condition for deciding the cable size,

    the point number one is correct, accepted.
    but the point number three is not correct i believe. because, once we accept the first point and third point, then, the number of cable run will be always one. there is no way to get more than a run at any circumstance. but i have seen many projects and I myself installed more than a run, esp. transformer to LV panels there will be min 2 or more runs of single core, and many other areas.

    so, I request you to reconfirm it and edit if I am right.

    thank you,

    once again I am appreciating your service.

    thank you,
    [email protected]

  82. Chris Wilken
    Nov 06, 2016

    Good morning

    I would like to know how to accurately calculate cable diameter for DC systems.
    Can you help me please?



  83. esam
    Sep 25, 2016

    Good morning
    please advise how can I calculate voltage drop for circuit contains three phase and single phase load : example,, main cable 300 mm2 and connected to MDB , from MDB there is sub DB connected with 3phase load 80KW and SUB DB connected with 1phase loads average 3 KW (10 No’s).

    • engr gd warraich
      Nov 09, 2017

      first of all calculate distance i think under 100feet no voltage drop ocuure
      if ur distance more then 100 feet then divivde it to dividions

      ur total load 110 kw
      calculate total amount of current with three phase formula and for single phase it is nessory take in account for phase balancing

  84. Palanikalvarayan
    Sep 07, 2016

    Hello I am working in Oman New job construction electrical working here total 5 floors each pilot 1 st floor 5 rooms apartment total room 25. apartment total watts 350 kw cable size and mdb smdb mcc pdb ldb how many cable size details diagrams ground floors snapping mall please need yours helped so I am waiting for your reply as soon as possible thanking you

  85. ummer
    Aug 09, 2016

    i want to know 220VAC,50Hz motor will work with 220VAC,60 Hz without any problem.

  86. Liyakat ali
    Jul 29, 2016

    Dear sir
    1. How can i detremine Power Factor Pannel.
    Supose our load 500 kva. Than which type of KVAR pannel install.
    2. How Can i check cable size

  87. Brenton B
    Jul 11, 2016

    i want to size a cable for a class project with a voltage drop of 2.5% 220volts 2000amps at 15meter run
    whats the best formula to use?

    • Linta kateme
      Jan 26, 2021

      How to calculate the minimum size of the cable

  88. selvamani
    Jul 05, 2016

    Dear sir,
    How can calculate power cable AMP capacity? Wich is formula use this calculation standard.
    For example 185sqmm 4core cable what is AMP capacity how calculate?
    Please give me feed back in my mail sir.


  89. manas pal
    Jun 29, 2016

    What is the code you have followed can you please mention? Please send me snap of the code.

    Jun 08, 2016

    Dear sir,
    I would like to know how can calculate power cable AMP capacity? Wich is formula use this calculation standard.
    For example 50sqmm 4core cable what is AMP capacity how calculate?
    Please give me feed back in my mail sir.


    May 06, 2016

    Sir, I have a query about the 4th condition regarding cable short circuit capacity and system short circuit capacity. In case 2 you have taken system short circuit capacity(6.0KA). how to find it?

  92. lusekelo
    Apr 26, 2016

    very helpfull information Thank you

  93. Murali
    Apr 25, 2016

    Very good..informative topic.. basic information for all electrical engineers..

  94. VISHAL
    Jan 19, 2016

    1.In that formula cable length is multiplied with 100
    2.why we multiply that?
    3.if we are using it for converting meter in to millimeter means we should use 1000?
    please clear my doubt

      Mar 30, 2016

      It might be % voltage drop. That’s why 100 is put there for %.

    • shyam sharma
      Apr 29, 2016

      this 100 is used for %age VD calculation and not to convert cable length in mm.

      • Teekay
        Aug 29, 2017

        Also, the divsion by 1000 is for converting the impedance of the cable / km to a value corresponding to 200m of cable length.

        How did you find the short ckt capacity of the cable at the load point as 6.0kA?
        Could you show the steps to it please?

  95. sumith ranaweera
    Jan 15, 2016

    Thanks..this topic its very useful for us.

  96. Niraj
    Nov 30, 2015

    Dear Sir,

    I have some doubts related to cable sizing,
    1- Why we do cable sizing calculation on connected load ?
    2- If we use the APFCR can i do the calculation with .95 pf.

    • Linta kateme
      Jan 26, 2021

      1 we normally calculate cable sizing in order to know the current carrying capacity of the cable

  97. marko peter
    Oct 15, 2015

    I have draw the 350 dc current , so what is the size of the cable i can use? give me answer with formula?

  98. Tlou
    Oct 11, 2015

    Dear sir

    Please clarify me 3.5 core. How can i identify it?

  99. inderpal
    Sep 17, 2015

    Dear sir,

    What should be the size of cable used for connection of lightning rods,
    Can you please suggest us with some example.

  100. Vijay
    Sep 17, 2015


    I would like to know how to calculate the cable sizing for UNDERWATER application (submerged in deepwell of 220m) load details are Electrical Induction Motor, 540Amps, 0,85PF, 440V, ThreePhase, Voltage drop 3% ,Water Temperature 56 deg.C, 3 cables tied to steel column pipe of 200m.

    Sep 08, 2015

    Dear sir,
    I would like to know how can calculate power cable AMP capacity? Wich is formula use this calculation standard.
    For example 50sqmm 4core cable what is AMP capacity how calculate?
    Please give me feed back in my mail sir.


  102. parthasarathy chellappan
    Aug 30, 2015

    Sir, i am working in saudi arabia. i want to purchase your electrical notes. i can send the money through the money transfer agencies. i want the sending details

  103. sohail malik
    Aug 17, 2015

    sir can u pls send me table of standards for calculation of every type of cable … wither we are calculating it for room or industry etc
    God bless

  104. Sachin
    Aug 15, 2015

    Excellent , sir

  105. Syed Asif
    Aug 01, 2015

    Dear Sir,

    My Q is why did u use 139 A to calculate Volt drop formula for 70,95sqmm cables??.
    why dint you apply the actual current rating for the cables viz 170,200 A respectively.I mean these are the cables we are selecting so why not use their rating in the formula??
    Pls explain

    Jul 17, 2015


  107. Waqas
    Jun 14, 2015

    Thats a really good writeup, clears many misconceptions regarding cable sizing. For all those asking for standardized tables for wire gauge and ampere capacity I recommend to search websites of your local cable manufactures, I am in Pakistan so I downloaded the tables from Pakistan cables website.

  108. Mustafa Kaydawala
    Jun 09, 2015

    Dear Sir.

    I would like to know how to size a Transformer.

  109. Aqil
    May 28, 2015

    Sir, can we take the values for resistance and reactance for cable from the specs Manual of the cable to be used?

  110. Eng.mohammad Alamawi
    Apr 21, 2015

    May i ask how did you chose the Amp capacity of the cable in both cases ??

  111. Arnie A. Bañaga
    Apr 14, 2015

    Good Day! Where did you get the tables? Please let me know where do you find this standard tables that you used. Thanks!

    • Sushil Kumar
      Apr 14, 2015

      Dear Sir, I don’t have the tables for resistance and reactance specified for under ground cable of different dia. So please attach the table also.

  112. kishore chandra sahu
    Apr 04, 2015

    Dear sir,
    please give the electrical motor cable calculation details .
    please send me my mail id.

    Thank you

  113. Murugeshwari
    Apr 04, 2015

    Dear Sir,

    I thoroughly understand the above expalined calculation. But i have one doubt ( where u took resistance , reactance & current carrying capacity Of cable ) if it has any tabulation pls send it to my email ID.

  114. Nabeel Ahmad
    Apr 03, 2015

    Sir I’m Nabeel ahmad I want to ask how did u get capacity of cable like is 170A &resistance of cable . Tell me also about derating factor.
    Email [email protected]

  115. Deepak kr. Mishra
    Mar 30, 2015

    Very much interesting & useful

  116. Emile
    Mar 30, 2015

    With regards to the statement:
    “If we select 2 runs, than voltage drop is 2.8% ….”

    How did you derive at 2.8%
    Could you provide the formula , step for step calculation used

  117. saad
    Mar 22, 2015

    thank you

  118. Mahesh
    Feb 23, 2015

    Dear Jignesh,
    I am mechanical engineer from VJTI, Mumbai; I want to install 100 cameras at 100 mtrs distance on 6mtrs high poles around the agriculture land. Each camera will be operating at 12 volts and carrying 1 amps; please can you guide me about the cable size to supply power to all 100 poles. The circumference of the field is about 10 kms.

    • Kristian Malihan
      Feb 26, 2015

      HI Jignesh,

      May i ask what type of camera is it IP or Conventional Camera(coaxial)?
      is your are you using AC 12V or DC 12V?

      I think i could help you with this just provide me some information. you could email me also.

      Kristian Malihan

  119. Samira
    Feb 20, 2015

    Hi Jignesh,
    This is Samira, Electrical engineer. I read your comments on how to calculate cable size. Thank you.
    I have a couple of questions for you; can you please help with the answers?
    • Can you please explain voltage drop calculation in single-phase system as well?
    • What is the source of these tables? I need to have a handy copy of the reference please for my projects. Some of my cables are in the air in an indoor warehouse.
    • Can I ask how did you get current capacity of 70 mm cable? Also I have same question about its resistance & reactance.
    Please email me on ‘[email protected]’.
    Thank you,

    • Samira
      Feb 26, 2015

      I got my answers via investigation on net & your webiste, thank you

      • sri venkatesh
        Mar 10, 2015

        Can I ask how did you get current capacity of 70 mm cable? Also I have same question about its resistance, reactance, short circuit capacity of the cable.
        please give me answer to this mail id- [email protected]

  120. prathap
    Feb 06, 2015

    how to calculate derating facter please mail me

  121. singaraj
    Dec 22, 2014

    these grouping factor ,cable correction factor & distance factor you shown the table here
    how do you prepared (0.6,0.8,1,1.2)like this , what datas you have to prepare these things
    can you post.
    give me a reply.

  122. MOhan
    Nov 11, 2014

    Thank you for the information

  123. D K Nagpal
    Nov 05, 2014

    Dear Sir,

    I Need sofftwre for cable size calucations. Please advise.

  124. saravanan
    Oct 25, 2014

    Thanks a lot for sharing your experience ……….I want you to share your experience on factory electrical cable selection , DSL bus bar selection , cable size , current carrying capacity of cable , mcb selection

  125. Engr Muhammad Tanveer
    Oct 22, 2014

    Thanks a lot for sharing your experience ……….I want you to share your experience on building electrification of high rise buildings and what are the factors that as electrical engineer you should be considered.

  126. Kashif
    Oct 18, 2014

    Kindly Provide your email

  127. Kashif
    Oct 18, 2014

    Dear Sir, I would like to be the Member of Institute of Engineers India. Kindly I need your reference for Membership

  128. vikash kumar singh
    Oct 09, 2014

    Thanks a lot for sharing ……….I have a doubt about how to calculate the fault level of Ht cable ……..plz reply

  129. Ateeq
    Sep 21, 2014

    Dear Sir , kindly Clear my Doubt for Applying Correction Factor to the size of the cable Why the Full load current is reducing when we apply correction factor .

  130. Marikkani
    Sep 18, 2014

    Dear Jignesh,

    Thanks for your contribution and its sure an good material for every persons.And let me request to please understand that the how the selection of current capacity vs cable size happens
    (3.5core 75 sqmm for 170A & 3.5 core 95 sqmm for 200A ) .let me request to please share 1 core .5sqmm to maximum cable 4 core size selection chart( as per Indian & International standards) in excel by which I shall go for my use.

  131. satheesh
    Aug 17, 2014

    Let me know ,in CASE 1 calculation how did you know the cos(pi) and sine(pi) value as 0.8&0.6.

    Any one plz clarify my doubt.

    • abhishek
      Nov 19, 2014

      you have power factor .8 , so cos(pi) will be .8 , then calculate value of angle(36.8698)
      By this again calculate value of sin 36.8698, which is 0.6

  132. turbold
    Jul 29, 2014

    Thank you for your information..From mongolia

  133. iman
    Jul 27, 2014

    Thanks, but I think this site is very basic and simple calculations are
    Thanks again for taking the time

  134. Ajay John
    Jul 27, 2014

    I wants to how this short circuit capacity of 8.2 and 6 kA are got? Regards

  135. kiranreddyk
    Jul 23, 2014

    Good article

  136. Umesh Charola
    Jul 16, 2014

    There is a small typo mistake.. Instead of 139, It should be 159 A.

    (1.732 · 139 · (0.57 · 0.8 + 0.077 · 0.6) · 200 · 100) / (415 · 1 · 1000) = 5.8%

  137. Melvin
    Jul 16, 2014

    sharing your experience with debuting engineers like me will be of great help. I hope to remain in contact with your scientific touches.

  138. Javed Akhter
    Jul 13, 2014

    Thanks Mr. Parmar for sharing the knowledge.

  139. gnanavel
    Jul 10, 2014

    I would be thankful to you for giving the best things in electrical and I appreciated for the same.

    Jul 06, 2014

    i want to say thanks to Mr. Jignesh Parmar bcause i gained lot of practical knowledge bcoz his publication in EEP website…. thaks and thanks lot sir,………

  141. Ahmad Monajemi
    Jul 05, 2014

    W/O looking at the calculation details, it looks like the VD calculated in using the load PF. Power Factor is primarily determined by load whereas line VD must be using the line conductors impedance.

  142. piyush
    Jul 03, 2014


  143. Czarjeff
    Jul 02, 2014


    Great article, same calculation is used here in oil & gas industry.

    Btw, just for your correction and so as not to confuse the readers. Please correct the typo error on this paragraph. The 70 in the second bullet should be 95

    “Let’s select 3.5 core 95 cable for single run, short circuit capacity = 8.2 KA.
    • Current capacity of 95 cable is 200 Amp,
    Resistance = 0.41 Ω/Km and
    Reactance = 0.074 mho/Km
    • Total derating current of 70 Cable = 200 • 0.93 = 187 Amp.
    • Voltage drop of cable =
    (1.732 • 139 • (0.41 • 0.8 + 0.074 • 0.6) • 200 • 100) / (415 • 1 • 1000) = 2.2%

    • hari
      Jan 05, 2016

      Dear sir,
      I would like to know how can calculate power cable AMP capacity? Wich is formula use this calculation standard.
      For example 300sqmm 4core cable what is AMP capacity how calculate?
      Please give me feed back in my mail sir.


    • Ameer Bakhsh
      Mar 28, 2018

      Dear sir I want to know about the formula you have used to calculate the voltage drop. My question is that how have you calculated resistance and reactance (or conductance mho/km) 0.57ohm/km and 0.077 mho/km respectively? What values have you taken for calculation? kindly tell me I’m very confused and also how have you calculated the value of short circuit capacity which is 8.2KA you have not mentioned the formula and calculation. kindly reply thank you
      Best regards;
      Ameer Bakhsh

  144. Sadiqkhan
    Jul 02, 2014

    Very nice to see the data.
    GREAT GOD will help you for better work for this n coming generation. Do some thing for India, in where the power supply company fault may come out with knowledge to them where they lost the electric current when supplying. Specially in village.

  145. Muhammad Junaid
    Jul 02, 2014

    can we neglect thermal correction factor (K4)???

  146. mohamed gamal
    Jul 01, 2014

    it is very inmportante data

  147. Michael
    Jul 01, 2014

    Thanks for this priceless Technical information. I want you to shed more light on the relationship between, design current, total derating factor, derating current and cable current carrying capacity. According to IEEE & BS 7671 (2011), derating current = design current Ib / total derating fator Kt. So, in the above calculation, I expect derating current to be = 139/0.93 9 (i.e 149.5A) .

    • Shahrukh
      Jan 17, 2019

      Hi Michael, As per your calculation you have apply the derating on connected Load where as in above calculation it is applied on the cable and not on connected load.

      If you calculate the derating current with IEEE method, you have to consider the actual current capacity of cables and not derated capacity.

      I hope you must have understood now.

  148. Irfan Ansari
    Jul 01, 2014

    its economical to use 3.5 core instead of 4 core. Because, in balance 3 phase network the current in neutral conductor is zero.

  149. OKK
    Jun 30, 2014

    Amazing that you can let this slip through without any proofreading!

  150. felix sandoval
    Jun 30, 2014

    Congrat, great information and issues. Very helpful.

  151. Muhammad Junaid
    Jun 30, 2014

    Why we use 3.5 core cable,instead of 4 core cable?

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