Earthed SMPS PCB with no earth wire in its mains input cable

[cupoftea]

We have a several kW three phase equipment sent to us by a customer. There is a control board on it which takes in the three phase and puts out isolated 24V and 15V rails etc, for 100W total.
These rails go off board to where they are needed.
This control board has no earth connection from the 3 phase mains input cable that goes to it. The earth on this board comes by way of its metal heatsink getting screwed to an earthed backplane. Screw holes with restrings then take the earth from the heatsink and put it round the board via the tracking to the Y caps.

Do you agree this is incorrect? ..

Earth must come in from the mains input cable, so that the common mode choke can filter the common mode noise going back to earth.

 

[BradtheRad]

The earth on this board comes by way of its metal heatsink getting screwed to an earthed backplane.

I'm reminded of alerts decades ago to electricians not to omit the neutral wire inside BX cable. This was flexible spiral-joint metal pipes. Junction boxes were normally steel instead of modern plastic. All of this was intended to provide safety ground. Thus the house wiring was entirely within metal protection.

An electrician might think he could substitute the piping as the return and save wires. However it's contrary to code standards. If merely one joint in the path were to break contact, the risk is to energize the shielding with house voltage.