Bus bar rating

Is there a thumb rule for aluminum /Cu Busbar as I had seen what we specify and other countries have some different grading. If it depends on purity normally what should be the thumb rule for xx% of Al/xx %ge of Cu as bus bars

Regards

If electrical conductivity (EC) aluminum is available (1050, 1060, 1199, 1350), use the rule given in letter 29456 (www.finishing.com/294/56.shtml) -- the aluminum area should be 1.6 times that of copper.

For non-EC alloys, increase the area in proportion to the resistivity (reciprocal of conductivity). Electrical Conductivity and Resistivity data is available from the NDT Resource Center at http://www.ndt-ed.org/GeneralResources/MaterialProperties/ET/et_matlprop_index.htm

Comments:
Al 6101 and 6063 are often used.
Although lower in conductivity, the T6 temper is preferred over annealed, as the higher yield strength better resists creep loosening of bolted joints over time.
The contact areas of aluminum busbar should be plated (silver or tin) or else cleaned and an electrical joint compound (EJC) properly applied.
Joint contact pressure should be at least 1000 psi.
It's generally a good investment to use a bit more conductor metal in order to reduce ohmic heating and to save on electricity over time.