Bars can be anything from a mandated .25"x2"x12" or greater on insulated spacers or something as simple as a standard grounding bus bar like a Square D #PKxxGTA style on (or not) an insulator kit (#PKGTAB). The size and such are dependant on the building, the equipment in the closet, the closet, and the specs. Same with the size of the conductor to the main service which depends on length also.
For very small buildings I would not size it smaller than the grounding electrode conductor and typically limit my contracts to #4 as a minimum size. This is just a general shot in the dark.
I do require the bonding of the racks as mentioned above, but also bonding is acomplished as needed through the cord sets. There can be ground loop problems with radio systems with this arrangement, but I have not experienced them yet.
Shane
