# Emmergency: Cable size calculation



## WalidAbid (Jul 14, 2012)

Good afternonn,
I am new member in this forum and it's my first participation that I hope will not be the last!
I'm a mechanical ingeenier and I'm looking for the complete and correct manner or formula to determine and calculate a cable section in a three phase circuit.
It will be very helpful to give a detailed calculation with detailed terms in such circumstances (I am not known in electrical calculation, but I have to make it during a present project):

Motor power: 8kW,
voltage: 415 V,
Nominal current: I= 22 A
cable length = 50m
ambiant temperature: 50°C

thank you in advance
Walid


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## chewy (May 9, 2010)

The answer is 42.


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## WalidAbid (Jul 14, 2012)

what's 42?
more details please


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## chewy (May 9, 2010)

Its bigger than the both of us Brother. Its the answer to the ultimate question.


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## Aussielec (Apr 1, 2012)

WalidAbid said:


> Good afternonn,
> I am new member in this forum and it's my first participation that I hope will not be the last!
> I'm a mechanical ingeenier and I'm looking for the complete and correct manner or formula to determine and calculate a cable section in a three phase circuit.
> It will be very helpful to give a detailed calculation with detailed terms in such circumstances (I am not known in electrical calculation, but I have to make it during a present project):
> ...


I'm not going to give you a calculation because I can't be bothered typing....

6mm2/10mm2 is the go. If it was me I'd be putting in 10mm2.


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## LARMGUY (Aug 22, 2010)

chewy said:


> The answer is 42.


Hee, hee! What is the meaning of life? Hitchhiker's GUide to the Galaxy.



> I am new member in this forum and it's my first participation that I hope will not be the last!
> I'm a mechanical *ingeenier* and I'm looking for the complete and correct manner or formula to determine and calculate a cable section in a three phase circuit.
> It will be very helpful to give a detailed calculation with detailed terms in such circumstances (*I am not known in electrical calculation*, but I have to make it during a present project):


Yeah right, and I just took my last tooth tonight for a fitty cent tip. Read the book next time kid.


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## TOOL_5150 (Aug 27, 2007)

why is this in structured cabling....?


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## WalidAbid (Jul 14, 2012)

*urgent!!!*

Good afternonn,
these are the motor and circuit data:

Motor power: 0.37kW,
Nominal current: I= 0.8 A
voltage: 415 V,
cable length = 80m
ambiant temperature: 50°C
Maximum voltage drop percentage =415*4% =16.6V

According to the Bahraini Regulations:
- temprature factor= 0.89
- core factor (3core cable)= 0.7

This is the calculation I did:
- target current=I/(0.89*0.7)=1,29A ==> 1,5A
when I check the current rated table, the suitable cable section will be 1.5mm but our contractor us a 2.5mm cable (I must verify his choice and prove that it's correct and submit the calculation to our consultant at least tomorrow morning!!!!)

According to the current rated table, we get: 
for the cable section: 2.5mm ==> current rating= 33A and Voltage drop /amp/m= 16

but when I calculate the Voltage drop /amp/m for my circuit, I find: 
mV= dV*1000/(target current *L)= 16.6V*1000/(1,5A*80m) = 138,33mV >16 (from the table)

Now, what I have to do?
I don,t know how to proceed and finalize the calculation!!

I have to make the verification for 20 different equipments with power variying between 0.37 and 48A!
Would you please help me and show me how to continue with the remainder calculation?

Your help is extreamly needed, I'am really blocked.
Thank you


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## chrisfnl (Sep 13, 2010)

You get what you pay for... as a professional electrical technologist, trained and skilled in the field of electrical design, may I recommend you hire an electrical technologist, trained and skilled in field of electrical design?


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## Dennis Alwon (May 9, 2009)

chrisfnl said:


> You get what you pay for... as a professional electrical technologist, trained and skilled in the field of electrical design, may I recommend you hire an electrical technologist, trained and skilled in field of electrical design?



I agree. I don't think it is wise for us to give info to an unqualified individual. Hire someone who is capable of doing this work. I am sorry but I am closing the thread according to forum rules.


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