This time i want shared about **how to sizing the electrical cable**.This topic is important because it’s involved with safety issue,cost and time line for the electrical installation project.

Cable or wire sizing matter already discussed for a long time ago and it’s a hot topic for Electricians and Engineers.So i hope from this post,it can give a clear view and understanding how to select current rating for wire,cable rating,voltage drop, and wire sizing for wiring project application

.From cable/wire sizing calculation we can estimate the proper size for cable to our wiring installation project.One thing that we need to prepared before cable or wire sizing is several data or information about wiring project includes :

## How to sizing the electrical cable/wire?

1) Type of load : For feeder,control panel,distribution board (DB) or motor

2) Power Source : AC /DC power for Three phase or single phase

3) Full load current (Ampere)

4) Circuit Breaker size

5) Types of cable ( PVC,XLPE,Fire proved)

6) Installation Condition ( Underground, trefoil,trunking,tray or conduit)

7) Distance / length of cable run from source to load

## Calculation for sizing electrical cable/wire

### Ib ≤ In ≤ Iz

Ib = Amperage load

In = Circuit Breaker size

Iz = Current rating for cable/wire

**Example :**

We plan to install 1 unit induction motor 75 hp for running a water pump.Power factor value is 0.8 and motor efficiency is 0.85.Power supply for this motor is 415 volt 3 phase 50Hz.Distance from panel to motor is 75 meter.This panel and pump is located at outside of factory.Please sizing the suitable circuit breaker,electrical cable and also type of cable for this application.

**Calculation**

### Ib ≤ In ≤ Iz

Ib = ( hp x 746) / (√3 x Volt x PF x Efficiency)

Ib = (75 x 746) / (√3 x 415 x 0.8 x 0.85)

**Ib = 114.5 Ampere**

In = Ib ≤ breaker sizing

In = 114 ≤ 150 ampere

**In = 150 ampere** (we decide to used MCCB 3 pole with 150 ampere rating)

Iz = In ≤ Iz

Iz = 150 ≤ Iz

**Iz = 187 ampere ( carried capacity for 50mm² cable size)**

So we decide to used cable size = 50 mm² with 4 core cable and clipped direct to cable tray.To confirm this cable size,we need to calculate the voltage drop.

* For full table of cable size,please download cable size chart / table below.Clink link to download PDF file for Cable Current Rating Table

## Voltage Drop Calculation

### Formula voltage drop : Vd = Ib x length(meter) x mV / 1000

Vd = (114.5 x 75 x 0.87) / 1000

Vd = 7.47 ( Acceptable refer to IEE 17th edition )

**Conclusion**

From this calculation, we fully confident to laying cable size** 50mm²** with **150 ampere** of MCCB,using **multicore PVC Armored cable** (due to outdoor wiring application) and also cable laying with cable tray.

That why all Electrician and Electrical Engineer need to know about cable sizing calculation to make sure wiring installation project successful and meet the requirement of Electrical Safety and Regulation without any disaster.

Thanks for distributing these useful technical information

Your welcome :D

Thanks for the valuble topics & expecting more subjects.

I’m glad to share :D You are welcome :D Please subscribe my feed for more interesting topic about electrical.

Your blog very useful. thank you very much

really appreciated what u did

Thanks…i’m glad to shared :D

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hi. i need cable sizing formula & star delta connection with wiring diagram…. take care

thanks for valuable information

I’m wondering why you didn’t choose a conductors of 35 mm2? , It gives you Ib ≤ In ≤ Iz

Thanks for information which are very important to us. We never consider the size of cables and wires – Eutex International INC

Hello bhai

you guys did a beutifull job.it just solve my problem.good job

how do i calculate for the circuit breaker required give the formular please

Hello Sir

I want the complete procedure for cable selection

Thanks a lot sir giving this technical information…

V…thanks…!

Thanks

Sir kindly provide the formula for single phase motor also

Kya hum 22 Gage ke jaga 23 ya 24 number ka gage istamal nahi ker sakte help me brother

Kya hum 22 number Gage ke jaga 23 ya 24 number ka gage istamal nahi ker sakte help me brother

30 air-conditioning units wired in parallel with an average of 10amps each……

Help me calculate the cable size needed to supply 3phase power to a distribution board n the probable MCB size……..

30 air-conditioning units wired in parallel with an average of 10amps each……

Help me calculate the cable size needed to supply 3phase power to a distribution board n the probable MCB size……..

N/B air-conditioning r 24000btu size

for 300amps we can use 400a tp mccb

Thank you so much sir given information… about cable detection…

air condition unit 4.5 TR I need cabal siz and isolater siz com amp

air condition unit 11.5 TR INEED CABAL SIZ and isolater com amp

air condition uni 8.5 TR nidd cabal siz and isolaters com amp

Current size k hissab SE or voltage drop k liye table yaad krni padegi kya sir

hi,i really like the calculation but i request for full procedure of how to calculation.

how did you get the answer equals to 187 ???? please reply

Thank you for your free message of electrical techniques

20 air-conditioning units wired in parallel with an average of 15amps each……

Help me calculate the cable size needed to supply 3phase power to a distribution board n the probable MCB size……..

N/B air-conditionin and cabal size

thanks for the information

What is 75HP Motor Earthing Wire Size

What will be capacity of neutral cable for 3000 KVA transformer? What is the Neutral cable size percentage of three phase wiring respect to phase?

thank you for your discreption methode , but I didn`t understand how did you geat the 150 amps for the mccb circuit breaker .

can you please explane that for me .

best regaurds.

eng. Abdolgabar Ahmed Mahmood

Thank you for your explanation, as the mater of fact the calculated current is 114.5 amps, and from the table, we get cable size of 25mm2 and current carrying capacity is 124 amps which is the nearest current value from the calculated one.

You used a cable size 50mm2 and a current carrying capacity is 187 amps which is completely different and far away from the value in the table.

please explain to me.

Best Regards.

Eng. Abdolgabar Ahmed .

can we use below formula

P=1.723 x V x I X COSphi