I would also look at running temporary brake wiring, along the floor away from other wiring, to the brake just in case your getting a leak either thru other cabling(induced ac voltages) or your having a under load break in the wiring so your voltages drop to the coil.
I've bumped this up as I think this should be your start maybe after you have tested the motor like JKH just stated. It appears that you have 2 phases shorting or overloading and those 2 are the ones id look at. Also make sure your arc shields are in place as they can track across them.
