The principle of EDM (Electrical Discharge Machining) is actually quite simple.
In the initial position, the workpiece on the table and the tool on the upper head are placed in the working position so that they do not touch each other.
In a pool filled with “dielectric fluid”, the workpiece and the tool are connected to a D.C. power supply by a cable.
A switch circuit has been added to this connection. When it closes, an electrical voltage forms between the workpiece and the tool. (Of course, this switch must be controlled.)