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Anonymous Poster

KA Selection

02/25/2011 9:33 PM

I have a INCOMIING 100A mccb TPN c/w ELR 25ka and have a lenght of 80M from MSB to DB cable sizing 70mm main subboard fault level setting at 45ka, i need a ka selection formula to justfy 25ka the design MCB AND RCCB both 63A DP per circuit with L1 43A, L2 32A, L3 44.3A. Appreciate if some one could provide me the formula for Ka and cable sizing.

Regards

Jeff
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Anonymous Poster
#1

Re: KA selection

02/25/2011 9:40 PM

Speaky Engrish!
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Anonymous Poster
#4
In reply to #1

Re: KA selection

02/26/2011 12:16 AM

Yes, thank you for your time to look into this.
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Anonymous Poster
#2

Re: KA selection

02/25/2011 11:12 PM

ka = (L1^2 + L2^2 + L3^2)^-3*(L1+L2+L3)/(L1*L2*L3)
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pnaban
Guru

Join Date: Jun 2010
Location: srilanka
Posts: 2725
Good Answers: 5
#3
In reply to #2

Re: KA selection

02/26/2011 12:11 AM

Can you prove it?.

__________________
 pnaban
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ramvinod
Guru

Join Date: Jun 2007
Location: chennai,India
Posts: 592
Good Answers: 19
#5

Re: KA selection

02/26/2011 12:57 AM

step1 Prepare Single line diagram

step 2 Enter cable size,length.

step 3 Get input fault level from utility provider.

step 4 Get the cable resistance and reactance

step 5 calculate the fault level at various points MSB,DB and load end.

step 6 Based on step 5,calculate the fault current at various points.

step7 Now check the interrupting rating of MCCB,MCB etc these rating should be greater than the fault current.

__________________
 Ramesh,Freelance Electrical/automation Consultant
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Anonymous Poster
#6
In reply to #5

Re: KA selection

02/26/2011 10:44 AM

Ravinod, have you had you humour glands removed?
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wareagle
Guru
United States - Member - New Member

Join Date: Jun 2008
Location: Alabama
Posts: 1604
Good Answers: 63
#7

Re: KA Selection

02/26/2011 2:35 PM

I am providing you with the method rather than a formula so you will never have to ask again. go here. The cable size required is larger enough to carry the load per your local code.

Similar answer as ramvinod
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Anonymous Poster (4); pnaban (1); ramvinod (1); wareagle (1)

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