An earth connection is needed when using externally powered Tekron products, as it ensures that surrounding IEDs and the product are commonly earthed, avoids ground loops, and gives a path for surges and transients to discharge to. This is essential both from a user safety and functionality standpoint, and it is why many IEDs come with an external earth stud.
When a Tekron product is powered over AC, this earth pathway is provided by the earth lead in the IEC connector.
When a Tekron product is powered over DC, a wire from the earth stud to a known electrical earth is needed to earth the unit.
Note - the paint applied to all cases of rack mounted units is non-conductive, so earthing the rack the unit is mounted in isn’t enough on its own, a connection is also needed from the rack to the unit's earth stud.