A question that is often asked is, where should a digital ground plane be connected (grounded) to the hardware housing? The first observation is that a metal enclosure plays a small role in controlling the fields associated with the logic. This control exists entirely with the logic ground plane and the routing of traces. It is still a good idea to connect the enclosure to the circuit ground plane, as allowing it to float raises all sorts of new issues. This connection should be made to limit equipment ground currents from flowing in the ground plane of the circuit board. This can be done by connecting the housing to the circuit common, where the secondary of the power transformer connects to the circuit board ground plane. This practice is shown in Figure 5.5.