Testing the Schaffner FN1394-10-05-11 power entry module with a multimeter shows continuity between the ground pin and the body of the module. Consequently, when the module is fitted into an aluminum panel (into a non-anodized, raw metal, opening), the chassis is connected to earth.
In this situation, is a separate safety earth setup necessary, as per this diagram?
the problem is that raw aluminum quickly forms an aluminum-oxide coating which is insulating. This is the reason for the recommended ground connection with a toothed washer to cut through the oxide coating and contact the metal.
The module appears to have a plastic front through which the screws go so the mounting screws will not provide a ground path, even with a toothed washer. The incidental contact of the module body to the edges of the opening will not prevent formation or break through the oxide layer so there will not be a good ground connection.
To ground the aluminum chassis, I highly recommend following the diagram.
As was already explained you must not consider assembly screws for ground connections. Grounding screws should have the sole purpose of grounding the component, because they might otherwise be removed by somebody who cannot recognize the grounding purpose.
Depending on your market you will find standards for grounding screws, like at least an M4 screw with tooth washer on a paint-free surface. And you'll need a ground symbol on the front side of the aluminum panel.
By the way, the front cover of your chosen mains input seems to be plastic and non-conductive.
The module mounting screws must not be used as the sole grounding connection to the case. Connect the grounding terminal on the back of the power entry module to the case.
