A system may comprise a frame, a pair of rolls with each of the rolls comprising a roll body having opposite ends and a circumferential surface, a plurality of teeth being formed on the circumferential surface, and at least a portion of the circumferential surface being electrically conductive. The roll may also have a roll shaft having end portions extending from the roll body, with each of the end portions extending from one of the ends of the roll body. The system may also comprise roll supports configured to support the rolls on the frame in a manner such that at least one of the rolls is movable to adjust a separation gap between the rolls, a detection apparatus configured to detect contact between the rolls, and a signaling apparatus configured to produce a signal indicating a change in electrical potential is detected by the detection apparatus.