A mechanical device for converting direct current into three-phase alternating current includes a contact unit having at least two receiving regions for receiving electrical energy as direct current and at least three output regions for outputting electrical energy as alternating current. A first receiving region contacts a positive pole of a direct current feed. A second receiving region contacts a negative pole of the direct current feed. A first output region provides a first alternating current, a second output region provides a second alternating current, and a third output region provides a third alternating current. A contacting unit receives the direct current and/or outputs the alternating current, and an assembly provides contact of the output regions with three phases of a dynamoelectric rotating machine. An isolator between two of the output regions and the contact prevents the contact from making contact with the two output regions at a same time.