A slip ring unit comprises a brush block with multiple brushes rotatable against a module with multiple sliding tracks. A position encoder is connected to the brush block and the module, for detecting the relative position between the brush block and the module. An evaluation unit receives signals from the position encoder and generates a position-dependent signal indicating wear. The evaluation unit has multiple wear counters assigned to multiple positions and/or sections of the slip ring. If a movement is detected within a certain section, the related wear counter is incremented to allow to monitor wear at slip rings that are not continuously rotating.