Calc advise

[ICE]

Ok,

Here is one for all you Big Guns of calcs...


I am doing 2391-10 at the moment and l finished my apprentership 20+ years ago, so as you can gather I am a bit rusty on the old class room thing...

All I want is for someone to explain to me in a very simple way how to do this calc and for what reason.

OK here it is:

S=√I2t/K

Can anyone help.



Cheers

ICE

 

[Spudnik]

... I am a bit rusty on the old class room thing...

You and me both

Lenny's the man..

He's only a young un'

 

[Guest123]

Hi buddy.

That is the Adiabatic equation used for working out the min size of all protective conductors.

There is info that you will need first to be able to work out the calc.


Check out this thread

http://www.electriciansforums.net/e...th-size-correct-using-adiabatic-equation.html

 

[Mark.W]

S = Nominal CSA of conductor.
I = Value (in Amps) for Fault current which can flow through a protective device. (Uo / zs)
t = Disconnection time of protective device. (ie 0.4 or 5)
k = a factor taking into account, resistivity, temp coefficient, and heat capacity of conductors. (a set factor for the type of cable used)

It is used to make sure that the cpc complies with the install and will be able to cope with a prospective fault current. An adiabatice equation.

it is in 7671 on page 128.

 

[ICE]

Re: Calc advise PLEASEEEEEEEEEEEEEEEE

Ok,

So where am I going wrong here?

System TN
Uo 230
Zs 0.38
K 115
t 0.4

230/0.38=605(I)

605 sq = 366025
366025 x 0.4(t) = 146410
Sq root of 146410 = 382.63559
382.63559/115(K) = 3.327266mm

so s= over 3mm ?

 

[Mark.W]

Exactly correct s=3.33mm2

 

[ICE]

Yeah,

It cant be right, it is a radial circuit with 1.5 mm single CPC with a Zs of 0.38

should t= 0.04 as in 40ms or 0.4 as in disconnection time for a final circuit, because if it was 0.04 it would work out correct?

I am thick.........


It is not 40ms it is 0.4s and it should be a minimum cpc of 4mm

 

[Mark.W]

Hi

Uo = 230
Zs = 0.38
K = 115
t = 0.4

Isquared = 230 / 0.38 = 605A

so s = SQRT((605*605)*0.4) = 382.64/115 = 3.33.

If it is a cpc of 1.5mm2 then it does not comply and you would have to install a cpc of 4mm2

What are you getting for Ze and R1 + R2? also how long is cable run?

 

[scotsparky]

The time you use is the accual time form the time current curves for the protective device . in appendix 4 of BRB i had fun with it while doing my 2391-02