This power configuration has some serious issues related to drives and safety.
Briefly, don't ever consider running a DC drive on this stuff. You will need a delta/wye isolation transformer with grounded center point ahead of the DC drive so the SCR's can switch switch the armature uniformly to ground. Running directly on the corner-grounded power would produce large charge/discharge currents to ground in the armature resulting in lots of commutator arcing and short brush life.
While you can run a PWM type AC drive on corner-grounded power, you must disconnect the input MOV's to ground and turn off the output fault and short circuit protection. It's a high price to pay since the drive is essentially unprotected on input and output. A delta/wye transformer is again recommended.
Finally, there are serious hazards that are unique to floating or corner grounded power networks. A grounded balanced wye network enforces 277VAC to ground on each phase which is low enough to not ionize most dusts. With a floating or unbalanced system, you can have as much as 500VAC to ground which often ionizes common dusts. The result is that you do your normal lockout/tagout procedure on a machine and, due to ionizing dust around the disconnect contacts on the two high voltage phases, the load side conductors can float up to full line voltage due to the leakage around the disconnect thru the dust. Contact with the locked out equipment conductors puts you in contact with 480VAC. I almost lost my life due to this on a rubber extruder and have campaigned against this kind of power distribution ever since. For those of you that have to work with the floating or unbalanced networks, I recommend a four-legged ground strap. Connect the first leg to ground first, then the remaining three to the three disconnected (load side) conductors. Then you are sure they are grounded and stay grounded. This is standard procedure with electric utilities on their floating high lines. It becomes necessary for safety at 480V too if the network floats or is corner grounded.
One other safety consideration on floating systems. You probably have a CAT III 1000V meter in your tool kit. So you would think that it is adequate for safe contact with the power line. But, if it is a floating delta, you only know what the phase-to=phase voltages are. What is it to ground? Zero, 500VDC, 2000VAC, or maybe there is an insulation defect in the distribution transformer and the secondary delta network if floating at 4160VAC to ground. Maybe that meter isn't as safe as you thought it was! See my point?