## 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**.

### 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 Temperature | Insulation | |

PVC | XLPE/EPR | |

10 | 1.22 | 1.15 |

15 | 1.17 | 1.12 |

20 | 1.12 | 1.08 |

25 | 1.06 | 1.04 |

35 | 0.94 | 0.96 |

40 | 0.87 | 0.91 |

45 | 0.79 | 0.87 |

50 | 0.71 | 0.82 |

55 | 0.61 | 0.76 |

60 | 0.5 | 0.71 |

65 | 0 | 0.65 |

70 | 0 | 0.58 |

75 | 0 | 0.5 |

80 | 0 | 0.41 |

#### Ground Temperature Correction Factor (K2)

Ground Temperature Correction Factor: K2 | ||

Ground Temperature | Insulation | |

PVC | XLPE/EPR | |

10 | 1.1 | 1.07 |

15 | 1.05 | 1.04 |

20 | 0.95 | 0.96 |

25 | 0.89 | 0.93 |

35 | 0.77 | 0.89 |

40 | 0.71 | 0.85 |

45 | 0.63 | 0.8 |

50 | 0.55 | 0.76 |

55 | 0.45 | 0.71 |

60 | 0 | 0.65 |

65 | 0 | 0.6 |

70 | 0 | 0.53 |

75 | 0 | 0.46 |

80 | 0 | 0.38 |

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

Soil Thermal Resistivity: 2.5 KM/W | |

Resistivity | K3 |

1 | 1.18 |

1.5 | 1.1 |

2 | 1.05 |

2.5 | 1 |

3 | 0.96 |

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

Nature of Soil | K3 |

Very Wet Soil | 1.21 |

Wet Soil | 1.13 |

Damp Soil | 1.05 |

Dry Soil | 1 |

Very Dry Soil | 0.86 |

#### Cable Depth Correction Factor (K5)

Laying Depth (Meter) | Rating Factor |

0.5 | 1.1 |

0.7 | 1.05 |

0.9 | 1.01 |

1 | 1 |

1.2 | 0.98 |

1.5 | 0.96 |

#### Cable Distance correction Factor (K6)

No of Circuit | Nil | Cable diameter | 0.125m | 0.25m | 0.5m |

1 | 1 | 1 | 1 | 1 | 1 |

2 | 0.75 | 0.8 | 0.85 | 0.9 | 0.9 |

3 | 0.65 | 0.7 | 0.75 | 0.8 | 0.85 |

4 | 0.6 | 0.6 | 0.7 | 0.75 | 0.8 |

5 | 0.55 | 0.55 | 0.65 | 0.7 | 0.8 |

6 | 0.5 | 0.55 | 0.6 | 0.7 | 0.8 |

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

No of Cable/Tray | 1 | 2 | 3 | 4 | 6 | 8 |

1 | 1 | 1 | 1 | 1 | 1 | 1 |

2 | 0.84 | 0.8 | 0.78 | 0.77 | 0.76 | 0.75 |

3 | 0.8 | 0.76 | 0.74 | 0.73 | 0.72 | 0.71 |

4 | 0.78 | 0.74 | 0.72 | 0.71 | 0.7 | 0.69 |

5 | 0.77 | 0.73 | 0.7 | 0.69 | 0.68 | 0.67 |

6 | 0.75 | 0.71 | 0.7 | 0.68 | 0.68 | 0.66 |

7 | 0.74 | 0.69 | 0.675 | 0.66 | 0.66 | 0.64 |

8 | 0.73 | 0.69 | 0.68 | 0.67 | 0.66 | 0.64 |

**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:**

- Cable derating amp should be
**higher than full load current of load**. - Cable voltage drop should be
**less than defined voltage drop**. - No. of cable runs
**≥**(Full load current / Cable derating current). - 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 Sq.mm cable for single run.**

- Current capacity of 70 Sq.mm cable is:
**170 Amp**,

Resistance = 0.57 Ω/Km and

Reactance = 0.077 mho/Km - Total derating current of 70 Sq.mm 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%**

**70 Sq.mm 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 Sq.mm 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 Sq.mm cable for single run, short circuit capacity = 8.2 KA.**

- Current capacity of 95 Sq.mm cable is
**200 Amp**,

Resistance =**0.41 Ω/Km**and

Reactance =**0.074 mho/Km** - Total derating current of 70 Sq.mm 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 Sq.mm cable, cable selection condition should be checked.**

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

95 Sq.mm cable satisfied all three condition,

so it is advisable to use 3.5 Core 95 Sq.mm cable.

Md. Samsul Arefin

How can we calculate the Reactance of a 3.5 core 95 Sq.mm 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.

Paresh

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.

Joseph Gyebuni

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 sq.mm 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.

Nkosinathi

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

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.

Hozan

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

Muhammad Asad Basit

Dear Sir,

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

Regards

s.m shahiduzzaman

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.

santhakumar

Sir,

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,

santhakumar

+96897882004

santhakumar.ind@gmail.com

Chris Wilken

Good morning

I would like to know how to accurately calculate cable diameter for DC systems.

Can you help me please?

Regards

Chris

esam

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

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

Palanikalvarayan

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

ummer

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

Liyakat ali

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

Brenton B

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?

selvamani

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.

Thanks

manas pal

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

MANIK CH.BHANDARY

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.

Thanks

MAHARSHI

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?

lusekelo

very helpfull information Thank you

Murali

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

VISHAL

I HAVE A DOUBT IN VOLTAGE DROP OF CABLE.

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

ANIL GHILDIYAL

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

shyam sharma

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

Teekay

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?

sumith ranaweera

Thanks..this topic its very useful for us.

Niraj

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.

marko peter

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

Tlou

Dear sir

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

inderpal

Dear sir,

What should be the size of cable used for connection of lightning rods,

Can you please suggest us with some example.

Vijay

Hi,

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.

NARENDRA MISTRI

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.

Thanks

parthasarathy chellappan

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

Edvard

You can subscribe to complete technical articles and receive them right on your email:

https://electrical-engineering-portal.com/subscribe-to-full-technical-articles

sadiq

pleas i want equation of voltage drop of D.C current and its sources (from where its cames)

sohail malik

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

Sachin

Excellent , sir

Syed Asif

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

JAIPAL SINGH

KINDLY CONFIRM HOW TO DO THE HIGH VOLTAGE TESTING OF 33KV CABLE OF 16KM LENGTH.

Waqas

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.

Mustafa Kaydawala

Dear Sir.

I would like to know how to size a Transformer.

Aqil

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

Eng.mohammad Alamawi

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

Arnie A. Bañaga

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

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.

kishore chandra sahu

Dear sir,

please give the electrical motor cable calculation details .

please send me my mail id.

Thank you

Murugeshwari

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.

Nabeel Ahmad

Sir I’m Nabeel ahmad I want to ask how did u get capacity of cable like 70sq.mm is 170A &resistance of cable . Tell me also about derating factor.

Email me.nabeelahmad912@yahoo.com

Deepak kr. Mishra

Very much interesting & useful

Emile

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

saad

thank you

Mahesh

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

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

Samira

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 ‘samira.namin@gmail.com’.

Thank you,

Samira

Samira

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

sri venkatesh

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- venkatesh5476@gmail.com

prathap

how to calculate derating facter please mail me

singaraj

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.

MOhan

Thank you for the information

D K Nagpal

Dear Sir,

I Need sofftwre for cable size calucations. Please advise.

saravanan

Sir,

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

Engr Muhammad Tanveer

Sir,

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.

Kashif

Kindly Provide your email

Kashif

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

vikash kumar singh

Sir,

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

Ateeq

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 .

Marikkani

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.

satheesh

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

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

turbold

Thank you for your information..From mongolia

iman

Thanks, but I think this site is very basic and simple calculations are

Thanks again for taking the time

Ajay John

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

kiranreddyk

Good article

Umesh Charola

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%

Melvin

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

Javed Akhter

Thanks Mr. Parmar for sharing the knowledge.

gnanavel

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

N R VENKATESAN

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,………

Ahmad Monajemi

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.

piyush

good

Czarjeff

Hi,

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 Sq.mm in the second bullet should be 95 Sq.mm.

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

• Current capacity of 95 Sq.mm cable is 200 Amp,

Resistance = 0.41 Ω/Km and

Reactance = 0.074 mho/Km

• Total derating current of 70 Sq.mm 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

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.

Thanks

Ameer Bakhsh

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

Sadiqkhan

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.

Muhammad Junaid

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

mohamed gamal

it is very inmportante data

Michael

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) .

Irfan Ansari

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

OKK

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

felix sandoval

Congrat, great information and issues. Very helpful.

Thanks

Muhammad Junaid

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