How to Select Bus Bar Rating?

The rating of copper bus bar are decided by their cross sectional area. The current density of copper is taken 1.6 so multiply the cross-sectional area by 1.6, this will give the current ratings for copper bus bar

I would strongly disagree with any effort to size bus bars with thumb rules like so many amperes per sq.mm, etc. Bus bar deisgn is a Science & it is an art too. You have to consider many parameters:

i) Continuous current rating, duly taking into account various rating factors for temperature, enclosure, proximity, grouping factors, etc.

ii) Short time withstand current rating

iii) Dynamic Short circuit withstand capacity

dear ,

Bus bar rating is selected by following parameters

1. Maximum operating current - to calculate with load date.

2. Harmonics in system - they are playing a great role now a days, normally 25% derating of the bus bar is done to take in to this effect.

3. Maximum Ambient Temperature in side the chamber - 40 deg. C reference as per IS

But, you may have to derate with the geographical conditions.

4. Permissible Temperature rise of the bus bar at full load. - normally, 30 deg.C

5. Considering the above factors, size of the bus bar may be selected by taking the

references of the data sheets.

Current carrying capacity is just ONE parameter of busbars. Even in this, a generalisation of taking a ballpark A/sqmm may lead you astray. Short-circuit withstanding capacity is a major parameter also. Also, skin and proximity effects, how many parallel conductors per phase, whether they are matt-black painted for better radiation, so many things play a part in busbar design. There are many threads in CR4 itself where experts have given lots of useful data. You can search for those threads by typing "Busbar" in the 'Search this forum' on the right.

Here is one thread for example, very good links : http://cr4.globalspec.com/thread/56152

Yes I agree with the comments of electricalexpert65. You have to consider all these factors for bus bar selection. The answers can be more specific and useful if the questions are little more eleaborated. Now the question is which bus bar? where it is to be used? etc

Dear,

Most of the deciding factors have been mentioned in the mails from experts. I would like to add one point. And that is short circuit heating of the bus bars. Once a size has been arrived at after applying all the appropriate derating factors, bus size must be checked/ cross checked against the rise in temperature during a short circuit. This is done by using Nomograms. If fault current, duration of fault current, initial & final temperatures are known, you can directly find out conductor cross section using the Subsidiary and Main Nomograms. Nomograms can be obtained from bus bar manufacturers.

Raina