Bus Bar Current Ratings
Bus Bar Current Ratings
(OP)
I am looking for a general technique or formula to find the current rating for bus bars in both copper and 1350 aluminium.
I have heard of general A/mm^2 but am not sure of numbers and it seems a rough approximation not to include temperatures, looking through all of my text books from back at uni days doesnt actually give any numbers for bus bars, just tables of expected ratings for cables.
Does anyone have a formula to use.
Thanks
I have heard of general A/mm^2 but am not sure of numbers and it seems a rough approximation not to include temperatures, looking through all of my text books from back at uni days doesnt actually give any numbers for bus bars, just tables of expected ratings for cables.
Does anyone have a formula to use.
Thanks






RE: Bus Bar Current Ratings
RE: Bus Bar Current Ratings
RE: Bus Bar Current Ratings
It was exactly what I was after and gives me both a starting point and a final rating and can use the formula from cda.org.uk for 1350 aluminium knowing its properties.
I was surprised I couldnt find something like this from google or the text books I have.
Thanks again.
RE: Bus Bar Current Ratings
I can use some of the formulas,
but it is still a great help.
RE: Bus Bar Current Ratings
Regards,
TULUM
RE: Bus Bar Current Ratings
Thermal designs can result in considerable reduction in conductor size.
RE: Bus Bar Current Ratings
Obviously there are more factors to be taken into account to change this value but it provides a starting point for me which is what I asked for, looking at the standards from NEC, 1000A/sq inch is the maximum for copper and 700A/sq inch is the maximum for the 1350 aluminium.
I was surprised to see that there was only a 30% difference between the two considering the resistivities are 40% apart. I am currently running the number to make sure it will work out to be equivalent to the existing copper design.
I still need to investigate other factors like the dangers using aluminium instead of copper such as short cct currents, arcing, joint methods, electromechanical stresses, configuration of bars etc.
I cant seem to find any reason why not to use aluminium except for the size, but weight is more important to me than size.
Thanks
RE: Bus Bar Current Ratings
If it is manufactured correctly and not used in a corrosive environment, aluminum can be as reliable as copper.
RE: Bus Bar Current Ratings
Now, you can build a minimum buss to support whatever current you want and use it if you do temperature rise testing. This is not easy to calculate because you need to figure out how much heat can dissipate through the buss duct or enclosure to the outside air. As an example, we have used 1/4" x 2" copper buss to support 800A which is 1600A/sq in. The temperature rise test passed so it is good.
I looked at a lot of buss different companies provided and could generalize and say the general pattern looked something like this;
800A = 1400A/sq in.
1200A = 1200A/sq in.
2000A = 1000A/sq in.
3000A = 800A/sq in.
Of course, these are not set in stone. You would still have to heat run test the bus bar.
As another note, when I talked to one engineer he told me how their tin plated buss just failed so they run the buss through the enclosure powdercoating line and paint it grey because that passes.
RE: Bus Bar Current Ratings
http://www.copper.org/applications/busbar/ampacity/bus_table3.html
RE: Bus Bar Current Ratings
Bill
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"Why not the best?"
Jimmy Carter
RE: Bus Bar Current Ratings
Sizing LV busbars is quite straightforward when they are in free air however when installed in an enclosure this is quite a different matter.
I have seen 2 x 150 x 6.3 busbars rated at 3000A in free air when enclosed burn down a switchboard at full load.
The CDA publication is quite useful but you are much better off with empirical data such as that provided in the Termate Guide.
For example in the guide 2 x 150 x 6.3 bars are rated at 3287A in free air but 2165A in still air. (I am assuming you are designing in accordance with BS EN 60947)
Another pitfall that is often overlooked is the heat contribution of the LV switchgear. A 3000A ACB at full chat will generate about 1kW of waste heat most of which ends up in the coppers.
Hope the above helped,
FPC