The spark erosion unit for operation on a workpiece (2) has opposing rotating column or tube electrodes (1), and a voltage is applied to the space between the workpiece and the electrode. It has a memory unit (10) for storage of reference times for short circuit determination, and a unit for altering these reference times dependent on the electrode rate of rotation. A unit (7) serves for short circuit detection, while a unit (9) determines the duration of a short circuit. This duration is compared with the data in the memory unit (10). A control unit (8) serves to avoid short circuit when the time determined by the unit (9) exceeds the stored reference value.
