Smaller metal parts in the form of staples, etc., are of no consequence. These smallest parts slide through the cutting gear without themselves being shredded. However, larger massive parts or foreign materials of any kind should be avoided in the cardboard boxes. It could lead to fatal consequences for the cutting unit and knives if larger metal parts were to get into the cutting gear. Consequently, foreign materials of any kind should be avoided. The EKZ is equipped with a PLC module including an automatic reverse and cut-out control, which is integrated in the control system of the shredder. This module serves to protect the machine from damage of any kind in the event of overload or from the massive parts mentioned here.