Where do you ground on 100 amp panel?

A typical panel has three large wires entering the main panel from the electric meter and a bare ground wire. Two of the large wires are hot and go to the busses where the breakers are mounted. The third wire is common and is connected to one or more common bus locations. It will usually be silver in color with a screw on top to connect white wires from branch circuits. The ground is the metal of the panel itself and there will be one or more ground busses usually copper colored that are connected to the metal of the panel by screws there by "bonding" these ground busses to the metal of the panel. You should also see a copper wire coming from a ground rod connected to the metal of the panel.

At the main panel you need to bond the common to the ground. There is usually a screw that allows this bonding to occur. If you have subpanels ground and common are NOT connected at the subpanels.