Quick CPC calculation help please

[J@mes]

Just need convincing that I am still doing it right!

So,

16mm SWA, 50M run, 12Kw load 3P/N supply. (17.3A per phase)

16mm R1 + R2 = 1.15mOhms/Meter = 100x1.15/1000 = 0.115

ZS = 0.21 + 0.115 = 0.325

230/0.325 = 707A (fault current)



√ 707 x 707 x 0.1
---------------------
115 = 20.8mm?


Thanks

 

[Sintra]

I get 1.944mm using those figures in the adiabatic.

 

[J@mes]

Via a software calculation or by hand? If by hand, can you go through it with me?

cheers

 

[Sintra]

Right 707 * 707 * 0.1 = 49984.9

Take the square root of this and you get 223.573

Then divide this by 115

And you get 1.944

 

[J@mes]

Thank you - I see my mistake now - doing the 707x707x0.1/115 and then taking the square root of that. Basic maths error!

 

[Sintra]

No probs

 

[sean123]

wouldnt working out the pfc be 400/0.325 not 230/0.325. because its 3 phase? which would make the cpc size 3.38?

 

[J@mes]

I *think* you only consider a 1 fault scenario when calculating the CPC - is that right? It's how I've done it in examples I have written out when I did my 17th a few years back.

 

[sean123]

u are probably right, i think i just remember doing it like that in college thats all.

 

[J@mes]

Hopefully someone who knows for sure will let us know shortly!

 

[Guest123]

It would be 230V used in the calc.