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Calculation of Size of Transformer, Fuse and Circuit Breaker
Calculation of Size of Transformer, Fuse and Circuit Breaker

Size of Circuit Breaker & Fuse are as per NEC 450.3

This MS Excel spreadsheet calculates the following:

  1. Size of Circuit Breaker on Primary side of Transformer as per NEC 450.3
  2. Size of Fuse on Primary side of Transformer as per NEC 450.3
  3. Size of Circuit Breaker on Secondary side of Transformer as per NEC 450.3
  4. Size of Fuse on Secondary side of Transformer as per NEC 450.3
  5. Size of Transformer
  6. Transformer Full Load Losses.
Software:Calculation of Size of Transformer, Fuse and Circuit Breaker
Version:10.6.13
Developer:Jignesh Parmar
Size:90.3 KB
Price:Free
Download:Right here | Get Download Updates | Get Technical articles
Calculation of Size of Transformer, Fuse and Circuit Breaker
Calculation of Size of Transformer, Fuse and Circuit Breaker

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Page edited by E.C. (Google).

9 Comments


  1. Tony
    Oct 15, 2015

    What is mean by DF load in this page? How can we calculate the DF load?


  2. Cosy
    Jun 02, 2015

    I don’t want to repeat allready bespoken aspects. Just a reminder about ISO – standardized naming and abreviations for physical values:

    Kva : it must be written as kVA
    Amp : it must be written as A or Ampère
    Volt: in formulas and sheets simply V , or kV …
    Kw : it must be written as kW

    Power Factor and working points of losses should be keeped at values conform to IEC (as it takes matter in the most countries and nearly everywhere 50Hz is..)


  3. sakthibalan
    Oct 14, 2014

    how to calculate feeder short circuit current(KA)?kindly if u know mean inform me how to calculate this one


  4. Sahil
    Mar 21, 2014

    @Anmol978
    The ‘0.97’ is the stacking factor. The core is made up of Si steel/CRGO laminations due to which, some correction factor for the area is used.


  5. MANU
    Dec 02, 2013

    Dear Mr.Parmar,
    The spread sheet is ok. but the breaker selection is out of range as per the standards used. for example for 1000KVA breaker only 1600A breaker is sufficient. Please correct me if i am wrong. In the spreadsheet for 1000KVA 3000A is breaker suggest. Please check it


    • Shaukat Ali Khan
      Sep 05, 2014

      For 1000 KVA, 3-phase, 50Hz, 400V system:
      IL= 1440A
      So, the next standard breaker size would be: 1600A
      Since it is more than 800 or 1000A, it should be of ACB type.


  6. Eric.Bernays
    Sep 07, 2013

    Is there any difference between this standard and those within the UK?


  7. moon172011
    Jun 16, 2013

    this program make over design for breaker and this breaker out of standard range
    thank you for trying
    best regard
    Eng. the engineer


  8. Anmol978
    Jun 16, 2013

    I was just checking some State electricity Board inspection sheets on transformers. (Not related with spreadsheet) that while calculating the flux density of a transformer (MAX value is 1.600 T) a basic formula is used B=E(phase)/(A*4.44*f*N*.97), What is that .97 factor multiplied???
    P.s the above work is fantastic …

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