Designing circuits and voltage drop
According to the National Electrical Code, in order for general use circuits to operate reasonably efficiently, the maximum voltage drop for branch circuit conductors is 3% and for feeder and branch circuit conductors combined it is 5%. When designing circuits for sensitive electronic loads, it is important to account for a maximum voltage drop of 1.5% for branch circuits under full load and 2.5% for feeder and branch circuits combined under full load.
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%
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.
Suggested Leessons and course
Voltage Drop in Balanced Three Phase Systems
Voltage Drop in Unbalanced Three Phase Systems
Suggested Course
Voltage Drop and Fault Current Analysis Course For Power Engineers
Learn how to calculate voltage drop in single phase, balanced and unbalanced three-phase power systems and to analyze short-circuit currents. 18 lessons in 5h 16m total course length.
Voltage Drop and Fault Current Analysis Course For Power Engineers
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Jignesh Parmar
Electrical Middle management professional having more than 22 years rich and dynamic experience in Project Execution / Project Management / Designing / Maintenance diversifies from Electrical Power Transmission (400KV/220KV/66KV)- Distribution(11KV/220V) to Lifts-HVAC-Ventilation-Fire Fighting-Fire Alarm-Lifts-CCTV-Stack Parking Works (High Rise Buildings, Townships, Shopping Complex, Commercial Complex, School, Temple).Profile: Jignesh Parmar
1) IN 433V LT cable distribution ,Voltage drop verse’s power loss in the system calculation as well comparison required
examples (a) connected load 200kw (b) distance L -230 meter (c)underground armoured XLPE cables as per ISI approved.
You explain it very well, really informative. But please consider cable type ( aluminium or copper)
Thanks.
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?
Hi,
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!
How to calculate short circuit capacity of the cable?
In cable Sizing for the voltage drop calculation what is the formula for sin pi value . How will you find the sind pi value
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%
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
following:
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
sir pls help me how to find cable current capacity alluminium and copper.
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..
How we can calculate voltage drop for distributed network :
example :
Incoming from feeder pillar to meter room panel to No of connected load.
Why voltage drop 5% and 15% is permissible. Please reply.
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 %.)
Plz reply
What will be change in voltage drop calculation if we’re using cable for single phase applications?
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.
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.
I would love to join your group to improve my knowledge.
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?
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]
Eric
In which standard can I find these tables for the correction factors?
Different topics on improvement of electric distribution system and related calculations etc.
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?
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.
Yeah, voltage drop Calculation for 3.5C x 95 mm² is incorrect. it should be 4.3% instead of 2.2 %
This information is fantastic.
Thanks
Allowable voltage drop : 5%, Cable Length: 1300M, Motor power: 110KW. cable to be laid on tray in air
Cable size?
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
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.
Amp = KVA/(1.732*415) or
Amp = KW/(1.732*415*0.8)
Hope you understand the difference.
How we can calculate number of cables that can accommodate in a cable tray ?
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 .
95sq.mm 3.5 core cable which standard is this?
I love this platform. Looking forward to learning more from you genius.
I WANT TO BA AN ENGINEER AND WANT TO MAKE HUGE MACHINERY AND MAKE FREE ENERGY GENERATOR SYSTEM I LIVE IN GULSHAN RAVI
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)
It’s tabulated value. BS 7671:2018
U CAN FIND IT IN CURRENT RTING CHART
Why I couldn’t find current ratings chart
(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
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.
I need DC motor current rating chart
Instead of this, we can use a simple formula for 3 core cables – total connected load x 1.74 = load current
Sir, what is the figure 1.732?
Thanks for sharing.
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.
Sir, please let us know from which standard (IEC / BS / IS) you have taken the cable ratings.
(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%
Dear sir, how did you take system short circuit capacity as 6kA?
GREAT INFORMATIONS
Good day,
Please what is your reference for selecting resistance and reactance values
How we got 139 amperes after getting 170*0.93=158.10, calculation for derated current?
Some step is missing.
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
i need clarification how sin Value is 0.6? any calculation behind it?
yes there is calculation ,with formula that is sinǾ = SQRT(1-( cosǾ * cosǾ))
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
What the distance between load and supply ? What is the voltage value ? Pf ? And more. Are you serious about your question?
He has considered everything 200m length, 415 V voltage, Pf for converting Kw to KVA.
So what are you asking????
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.
Sir pl supply a cable size calculator EXEL Sheet.
generate 1250 kva and transformer 1200 kva the power haws 1600 A bracer what cable size
Thank u so much sir, such a wonderful messages.And please sir I need to know about how prepared load calculation and schedule?
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.
Hello sir, is there any formula to calculate the spare load in a electrical panel from the amperage values of branch circuit breakers.
Hello sir, are this factors applicable for UNINYVIN cables also.
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
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
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
sir kindly reply me how I simply calculate, how many amp.current taken by any ht or lt cable
Dear Sir
Please tell how to calculate the size of 11 kV distribution overhead aluminum conductor (ACSR) for particular load and distance.
Thanks
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. – ?
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
how to take the de-rating value for K1,K2,K3 K4,K5
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?
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).
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?
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
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))
cospi is power factor from there u can find sinpi using inverse cos formula
Ǿ depends on the load.
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
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
2.2% voltage drop calculated in this article for 95 sq.mm cable is wrong. Please recalculate & correct it. It comes out to be 4.32% & not 2.2%.
Thanks.
The voltage drop for 90 sqmm cabe 2.2% is wrong it should be 4.3 %
you are correct i got 4.3 too
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.
Can you tell me why you multiple Resistance and Reactance to 0.8 and 0.6?
Please
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
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
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.
I need the excel calculation sheets and correction factors
thanks
sir i want your excel sheet then pls send me
Respect sir. I guide cable size 1200 ft lengthfrom 63 transformer.15 hp 5 stage submersible motor .
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].
Thanks.
WHAT IS THE MINIMUM SIZE OF ARMOUR CABLE TO FEED 630AMPS DISTRIBUTION PANEL?
copper cable of 3core 150sqmm 2runs cable.
4Cx240mm2 XLPE + 1Cx120 mm2 will be sufficient to feed 630Amp.
could you attach cable capacity table and resistance/Km it will be so helpful
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.
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.
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.
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.
High drop in voltage is because of 1km cable length. Lay 240sqmm 2 runs to get with in 5% drop.
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:
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.
I need your Excel sheet. My mail id [email protected] and contct no.9682156495. Please contact with me.
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.
can I have that excel sheet? will thank you so much
my mail is [email protected]
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]
Aoa,
Sir Plez send me your excel Sheet For Calculating Cable Size and Voltage Drop
Good explaintion, but is it as per IEC, if so please give us the source of these tables, K1,2,3,4,5,6
Dear Sir,
you mention system short circuit current capacity is 6KA. Please tell me how to find the system short circuit current capacity.
Regards
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.
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
[email protected]
Good morning
I would like to know how to accurately calculate cable diameter for DC systems.
Can you help me please?
Regards
Chris
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).
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
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
i want to know 220VAC,50Hz motor will work with 220VAC,60 Hz without any problem.
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
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?
How to calculate the minimum size of the cable
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
What is the code you have followed can you please mention? Please send me snap of the code.
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
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?
very helpfull information Thank you
Very good..informative topic.. basic information for all electrical engineers..
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
It might be % voltage drop. That’s why 100 is put there for %.
this 100 is used for %age VD calculation and not to convert cable length in mm.
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?
Thanks..this topic its very useful for us.
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.
1 we normally calculate cable sizing in order to know the current carrying capacity of the cable
I have draw the 350 dc current , so what is the size of the cable i can use? give me answer with formula?
Dear sir
Please clarify me 3.5 core. How can i identify it?
Dear sir,
What should be the size of cable used for connection of lightning rods,
Can you please suggest us with some example.
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.
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
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
You can subscribe to complete technical articles and receive them right on your email:
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pleas i want equation of voltage drop of D.C current and its sources (from where its cames)
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
Excellent , sir
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
KINDLY CONFIRM HOW TO DO THE HIGH VOLTAGE TESTING OF 33KV CABLE OF 16KM LENGTH.
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.
Dear Sir.
I would like to know how to size a Transformer.
Sir, can we take the values for resistance and reactance for cable from the specs Manual of the cable to be used?
May i ask how did you chose the Amp capacity of the cable in both cases ??
Good Day! Where did you get the tables? Please let me know where do you find this standard tables that you used. Thanks!
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.
Dear sir,
please give the electrical motor cable calculation details .
please send me my mail id.
Thank you
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.
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 [email protected]
Very much interesting & useful
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
thank you
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.
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
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
I got my answers via investigation on net & your webiste, thank you
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]
how to calculate derating facter please mail me
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.
Thank you for the information
Dear Sir,
I Need sofftwre for cable size calucations. Please advise.
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
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.
Kindly Provide your email
Dear Sir, I would like to be the Member of Institute of Engineers India. Kindly I need your reference for Membership
Sir,
Thanks a lot for sharing ……….I have a doubt about how to calculate the fault level of Ht cable ……..plz reply
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 .
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.
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.
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
Thank you for your information..From mongolia
Thanks, but I think this site is very basic and simple calculations are
Thanks again for taking the time
I wants to how this short circuit capacity of 8.2 and 6 kA are got? Regards
Good article
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%
sharing your experience with debuting engineers like me will be of great help. I hope to remain in contact with your scientific touches.
Thanks Mr. Parmar for sharing the knowledge.
I would be thankful to you for giving the best things in electrical and I appreciated for the same.
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,………
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.
good
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%
“
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
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
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.
can we neglect thermal correction factor (K4)???
it is very inmportante data
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) .
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.
its economical to use 3.5 core instead of 4 core. Because, in balance 3 phase network the current in neutral conductor is zero.
Amazing that you can let this slip through without any proofreading!
Congrat, great information and issues. Very helpful.
Thanks
Why we use 3.5 core cable,instead of 4 core cable?