Busbar sizing: FORMULA, THUMB RULE, TABLE ?

September 29th, 2009 | Posted in Panel Building
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I’ve seen a number of “thumb rules” examples on CR4 forum :
“0.6 amps per sq mm in case of Aluminium and 1.25 amps per sq.mm for Copper”
” for Aluminum 0.8 amps for sq.mm, for copper is 1.25 Amps per sq.mm”
“0.6Amp/mm2 is fine for Alu, 1 Amp/mm2 is fine for OFHC Copper”

There are also some general dimensioning tables like the ones given by Copper Development Association.

Do you use such formulas or tables ? Which ones ? When and how do you use them ?

Add comments to share your point of view !

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Comment(s) to “Busbar sizing: FORMULA, THUMB RULE, TABLE ?”

  1. thannainglin says:

    I am an eng student,doing a thesis,to know about Design & calculation of busbar system,please sent me these datas and discuss the calculation .So pleasing U their link company (or)site.

    • Dan says:

      I do not know an existing place on the web which can be a real good reference on the subject, as per my opinion. If anybody knows about such place, please add in a comment here below !

    • ANIL KOTKAR says:

      for pcc/pdb panel Design & calculation of busbar system,please sent me these datas and the calculation formula & thumb rule for aluminium & copper busbar.

  2. K.ANGAMUTHU says:

    CURRENT CARRYING CAPACITY OF BUS BARS IS ALSO DEPENDS ON THE SHAPE OF THE BUS BARS (EITHER ALUMINUM OR COPPER). BEST SHAPE IS C- CHANNEL FORM I HOPE.

    K.ANGAMUTHU, PANEL BUILDER M/S MULTI TEK CONTROLS – COIMBATORE – SOUTH INDIA.

    • Dan says:

      Yes, you are right, among other parameters, the shape of the busbar can have a strong impact on its dimensioning. You can take a look at this article on this subject

  3. David says:

    2 amps per sq mm in case of Aluminium and 4 amps per sq.mm for Copper

  4. K.SIVAKUMAR says:

    I DO NOT SUBSCRIBE TO THUNB RULES OR ROUGH FORMULAE. I WOULD RATHER PREFER TO DO A DETAILED CALCULATION FOR BUS BAR SIZING WITH RESPECT TO THE CONTINUOUS CURRENT CARRYING CAPACITY (DULY CONSIDERING ALL THE RATING FACTORS), SHORT TIME THERMAL WITHTSAND CAPACITY AND SHORT CIRCUIT DYNAMIC WITHSTNAD CAPACITY. IF THE BUS BAR LENGTH IS CONSIDERABLE, I WOULD EVEN DO A VOLTAGE DROP CHECK.

  5. R. Murali says:

    Busbar selection criterion is very well explained in the book ” J & P Switchgear Handbook.” But in most cases, the rules followed and enforced by the local Electricity Authorities, Electrical Inspection authorities, and Fire and Safety authorities become the guiding factor in selection of busbars.
    R. Murali.

    • Dan says:

      In which country things are how you describe it ?
      I mean the fact that local authorities become the guiding factor for busbar selection/dimensioning?

  6. CESAR says:

    “thumb rules” are sometimes useful, but are not always adequate to fully understand the busbar sizing problem.
    Theoretically, a copper or aluminum busbars can carry the current you want, as long as the reached temperature not melt the material, this is an extreme case, but gives an idea of which is the limiting factor: the temperature!
    The success of a good sizing is based on a suitable configuration that can evacuate the excess generated heat by Joule effect losses .
    A large area, from the thermodynamics standpoint, can evacuate more heat than a small area.
    Therefore, the cross section is not the key is the ability to dissipate heat that defines the problem.

  7. Peter M says:

    With regard to sizing busbars using the various guidance tables.
    The best one I have found is provided by the copper development association.
    I have used this as guidance for many years when designing three phase copper busbar systems up to 6500 amps. However, these figures should only be regarded as a starting point. One of the largest variables at these current levels is the amount of ventilation you can introduce to these base figures.
    Without ventilation, the bars will be too small, whereas on the other extreme, if you introduce forced ventilation, you will be paying for copper you don’t need.
    Now that we have done that one, it must also be remembered that the various components connected to your busbar system will produce heat that also needs to be dissipated.
    The only sure way of sizing busbars is by testing, and possibly careful extrapolation of the results.
    Good luck.

  8. TEJAS DESAI says:

    K/a: Purchase Manager
    Dear Sir,
    We are pleased to introduce ourselves as a leading reputed manufacturer …

    • Dan says:

      I remind you that this blog is not for promotion, but to exchange experience, practices, news … about panel building profession. Readr the about this blog page for more details

  9. Peter M says:

    I thought this site was for technical discussion, not free adverts.

    • Dan says:

      I have erase the promotional comment from Tejas Desai.
      Thanks for being part of this blog community and for helping me to remind the scope of this blog !

      • PRABH CHAHA; says:

        Its my pleasure to b here with u guys. with your ques & answers my Knowledge is improving…

        Thanks

  10. Dear Dan,
    M workin as a Sr. Technician electrical in corporate sect in India. As par as I know there is a one site wich is might be usefull for you,
    http://www.lmphotonics.com
    Regards,
    Dhiren

  11. Peter M says:

    please guys, no more adverts or promotions.
    genuine technical discussion only.

    • Dan says:

      I took a quick look at the “lmphotonics” site, and my first impression is that there is some interesting information there (but also adverts) : some basic knowledge on motor starters, on power factor correction, a forum which may be of interest for panel builders : what do you think yourself ? others ?

  12. Peter M says:

    Good to have interesting sites pointed out, and indeed there is a plethora of interesting sites out there, if you have the time to wade through them.
    However I think we are in danger loosing the focus. The question asked was for help on how to size busbars.
    If we stick to the subject, I think the forum will remain useful, otherwise we are in danger of generating spam.

    • Dan says:

      I agree that the link from Dhiren should bring directly to content in line with the subject of this discussion (busbar sizing), and I will update this link as soon as I have the correct info from Dhiren.
      In parallel, as you say, it is good to have interesting sites pointed out ==> would you be ready to write an article here about the interesting sites you know about, which others could comment with their own ?

  13. Jeffrey says:

    We have recently added to our site a very useful guide to busbar design from a UK manufacturer Termate. Your readers may find this useful.

    Alternatively please visit the following web site to obtain an extract from the document, which has been described as been referred to by many consultants and manufactures as “the definitive guide to busbars”

    http://www.termate.com/termateguide.php

  14. HIMANSHU PARIKH says:

    We are the panel builder. We want to know how to calculate require distance between two support in main bus bar chamber with different combination inclusive of interleave arrangement

    • Peter M says:

      Termate do indeed produce some very good guidance on busbars, and if you work within the confines of their figures you will not go far wrong. However as I stated in my original comments, most tables are a good starting point but there is no substitute for testing, indeed to ensure your interperatation of any charts are safe, you must have your design type tested, see IEC 61439.
      To get back to your original question, have a look at the information published by both Termate and The Copper Development Association, I am sure you will find it very informative.

  15. BRNKK says:

    Thank you friends

    It is usefull for me a lot

  16. mik says:

    Dan excellent work
    Yes you are correct actually this is one of the subject in electrical engineering where different practices are used .NEC 125% BS IEC 145% and list is on . But i would like to appreciate that some one like you have already taken the step in this and what i like to to gather the authentic material at one place .
    Even many of us dont know how many types of type test and routine tests are used in PB .
    for busbar 1 A / mm² copper and 0.65 /mm² for aluminum is adequate .

  17. mik says:

    there is any chance for termate guide

  18. Peter M says:

    Contact Termate – Sales@termate.com, this guide is available at 24.95 GBP

  19. Craig McKee says:

    Sorry pressed submit too early.

    Regarding rule of thumb ratings eg 4A/mm etc, these really only work within a very narrow current band, for example at 6300A with 4A/mm = 1575mm^2, but this would not be capable of carrying anything like 6300A.

    We would not reccomend using a single figure, the termate guide gives ratings based upon tested configurations.

  20. sailendra singh says:

    sir
    i want to say that answer should also be visible on the website.
    thanking you

  21. Nilesh says:

    copper current capacity formula Pl. send me

  22. shanky says:

    ca anyone tell me which is the best hand book for electrical in which i can get all the information regarding electrical

  23. Peter M says:

    Read the comments from Jeffrey above.

  24. dhairyam says:

    if you know the bus bar calculations i.e how to choose the bus bar range for different voltage levels please tell me sir

  25. Yves Almell- says:

    could I recommand you to be link with our software of calculation based on IEC60439:
    http://www.erico.com/eriflex
    The advantage is that we offer also the busbar support solution and calculations depending of Short circuit value..

  26. gerrypinoy says:

    1 sq. inch is equal to 1000 amperes and convert sq. millimeter there on.

  27. himanshu says:

    we have 2000KVA transformer connected through bus bar from ACB .what will be the size of copper
    bus bar for better efficiency and safety purpose.Now in bus bar some time humming sound also coming.please guide and send your comments.Total length between them is 10 mtrs approximate.

  28. Raju Joseph says:

    Dear Friends,
    Any one can you help me to calculate the Flat Bus bar’s Current Carrying Capacity with Dimensions is thickness(P) x with(Q) x Length(R). please put some reasonable values in P x Q x R. i need example with full formula. the voltage is 11kv.
    thanks in advance,
    Regards
    Raju J

  29. Raju Joseph says:

    yes my fnd..

  30. Hayssam says:

    Anyone can assist me by provide me name of an application of software to calculate the size of required busbar, by providing the required Amps.

    I used to have an application on my previous laptop, but got stolen last week and I can not recall the name of that software.

    thanks

  31. Peter M says:

    Is this a question about busbars

  32. raju Joseph says:

    yes…

  33. raju Joseph says:

    yes Mr. Peter M

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