Suppose I have a variety of equipment which is variously powered from one
of the phases of a three phase supply. I'm concered about the potential
difference between two boxes on different phases. The boxes have low
voltage electrical connections between them (similar to USB ports).
Each box has a PC-style switching PSU. Leakage from the mains side into the
DC side could cause a high potential difference between boxes on different
phases, which would be enough to zap sensitive inputs on the
interconnections.

Suppose I connect the ground of the low voltage side of the PSU to that
box's chassis, and then bond all the chassis together and join that to
earth. Will that be sufficient to prevent any potential difference between
phases arising that could cause trouble with sensitive inputs?
Are there any issues this might cause (such as EMI, or tripping the RCD)?

Is there a common way to detect automatically that this earth bond has come
adrift (ie not by waitng for the annual PAT test)? I suppose checking for a
voltage between ground and earth, or putting a voltage across them and
checking the current hits some limit. But do people ever do this sort of
thing?

Thanks
Theo