Bus Bar selection

The size of the bus bar will depend on the current rating of the panel. You have to decide weather you want single double three or four bus bars to be used. The size will be different for DC and AC 50 Hz . AC rating will be slightly less.

As for example the rating given by a manufacturer is given. These ratings are for

30 °C ambient and 50° C temp rise over ambient :-

E-91 grade aluminum 25.4x 6.35 bus bar can carry

DC 356 A , 718A , 980 A , 1120 A for single, double,three and four bus bars

and for AC 50 Hz 366 A 715 A 970 A and 1110 A for one,two,three and four bus bars

The rating will vary with ambient and temp rise on loading the bus bar. By increasing the number of bus bars area of heat dispensing increases but heat radiation from the middle bar will be less . So while considering the calculation of bus bar rating the heat dispensing also must be taken care of. All other de rating factors also may be considered before deciding the bus bar size.

Current rating of my panel is 800A and it is to be used in 4bus bar (3Phase +1Nuetral), 415V, 50Hz. AC system. Can u tell me for alluminium bus bar how the size is calculated (Width and Thickness) or mm2 size if I know my Current level.

Hi achawla77,

Four bus bar means four plates to be used in parallel for each phase instead of one bar subject to availability of bus bars for large capacity panels . It does not mean three phase and neutral.

Now for 800 A load , single 63.5x 6.35 Aluminium bus bar is rated 812 A . if you want to add for de rating can go for 76.2x 6.35 which is rated 958 A .Depending up on the available size of bar in the local market you can make your own calculation of the size depending on cross sectional area.

Current rating of my panel is 800A and it is to be used in 4bus bar (3Phase +1Nuetral), 415V, 50Hz. AC system. Can u tell me for alluminium bus bar how the size is calculated (Width and Thickness) or mm2 size if I know my Current level.

The manufacturers of aluminium bus bars provide the current carrying capacity of their standard sizes. The charts are readily available. They provide their chart for specified ambient temperature and temperature rise. Depending up on your ambient temperature and rise of temperature you have to modify your max current carrying capacity and select the size of bus bar.

As an example one manufacturer provided me a chart of current carrying capacity for 35 ° C ambient Temp. and 30° c temperature rise :-

Size of bus bar 100x5 mm ( cross sectional area 500 sq mm ) current carrying capacity 820 Amps . This is a ready made chart provided by a manufacturer so I can depend on it as reliable.

Now you can add your factor of safety and other de rating factors depending up on your local conditions and decide either to go for the same size or to go for a higher size.

The next available size may be 80x 10 mm which has a current carrying capacity of 940 Amps. For these decisions you have to apply your skill and experience.

Al busbar carry 1.25A current per sq.mm. cross section. Hence if the current loading is 500A, then Al. busbar of 400 sq.mm. area should be used. The size of busbar can be 50 x 8 mm or 40 x 10 mm. Breadth of busbar is available in 10, 20, 25, 40, 50, 100 mm etc with thickness of 3, 5, 10, 20, 25 etc.

Can anyone please send me Bubar selection material such as calculator/charts etc

thanks in advance

Sunil

Generally current density considered for Aluminum Busbar = 1.0 A/mm2 & Copper = 1.5 A/mm2. You can apply the above to find out cross sectional area of the busbar based on feeder rating.