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 !
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.
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 !
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.
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
2 amps per sq mm in case of Aluminium and 4 amps per sq.mm for Copper
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.
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.
In which country things are how you describe it ?
I mean the fact that local authorities become the guiding factor for busbar selection/dimensioning?
“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.
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.
K/a: Purchase ManagerDear Sir,
We are pleased to introduce ourselves as a leading reputed manufacturer …
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
I thought this site was for technical discussion, not free adverts.
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 !
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
please guys, no more adverts or promotions.
genuine technical discussion only.
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 ?
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.
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 ?
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