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.

### Related Post

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

Hi,

I have gone through your site which is much relevant to my topic. Being a professional writer I want to contribute one guest article.

The article would be informative and hope your visitors like the article and shares on social platforms. The deal would be mutually beneficial to both of us and add value on both ends.

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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