# Electrical Cable/Wire Sizing

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

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

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.

## Voltage Drop Calculation

Below is a voltage drop calculation that i made for cable power supply from panel to induction motor.
From Panel to Induction motor = 75 meter
mV = 0.87 ( refer table below )

### 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 )

* Voltage drop acceptable value is 4% x 415 volt = 16.6 Volt

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.

1. Mohamed Shawer says

Thanks for distributing these useful technical information

• lemau says

• binu george says

Thanks for the valuble topics & expecting more subjects.

• lemau says

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

2. Amin says

Your blog very useful. thank you very much
really appreciated what u did

• lemau says

3. John Smith says

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4. saleem rasheed says

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

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

7. Govind kumar says

Hello bhai

8. Idowu Afekhare says

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

9. joseph says

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

10. raja says

Hello Sir

I want the complete procedure for cable selection

11. K.Niranjan says

Thanks a lot sir giving this technical information…

12. Arichandran says

V…thanks…!

13. Ashis says

Thanks

14. Maninder Preet singh says

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

17. James Abalah says

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……..

18. James Abalah says

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

• dhanu says

for 300amps we can use 400a tp mccb

19. Somanna says

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

20. mohammaed hoossain says

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

21. hemant says

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

22. richard says

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

23. syed bilal ahmed says

24. premperumal says

Thank you for your free message of electrical techniques

25. Sabir ansari says

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

26. odidi oluwafemi Gabriel says

thanks for the information

27. Rahul says

What is 75HP Motor Earthing Wire Size

28. Md. Aminul Islam says

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?

29. ASIF says

can we use below formula
P=1.723 x V x I X COSphi

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