We always float our 24V and 120V DC systems but the battery chargers we use (MDS power) have a voltage divider with the centre grounded. If there is 0V across the top resistor there is a positive ground fault, if there is 0V across the bottom resistor there is a negative ground fault. These conditions alarm on the HMI.
Recently the operators got fed up with the negative ground fault alarm coming up intermittently and actually traced the negative ground faults to two Bosch proportional valves, which incidentally were running twenty degrees hotter than the other ones.
While these are greenfield power plants with a copper ground grid under the building and substation and all rebar and metal in the building bonded to the ground grid, we have no problems with noise.
If we do encounter a device that internally grounds 0VDC we purchase a 24VDC-DC converter and feed it from its own isolated power supply to maintain the floating system. Parker proportional valves and brake pad wear detectors are the usual culprits.
The control panels have 24 DC, 24AC, 120DC, 120 AC, and 208 AC, but there are 600V motor disconnects with status contacts so we would have 600V and 24 in the same box in some places too. I imagine if 120AC or higher found its way on to the 24 system some devices would pop so the problem wouldn't go undetected and persist as a safety issue waiting to zap me.
Phoenix power supplies are meant to have the oomph to blow fuses.
We have also run in to problems in extremely large buildings where there is just too much voltage drop to trip breakers fed on #14.