The main aim of planning suitable maintenance interventions during operation of the technical equipment is to prevent a failure creation. Adequate maintenance of its individual elements can prevent the development of major failures, but also significantly increase the reliability and extend the service life. In general, the removal of a major failure of technical equipment is very much costly, but also time-consuming as carrying out the preventive maintenance at certain intervals. Therefore, these reasons compel us to deal with planned maintenance of technical equipment already in phase of design. However, the important question is determining an appropriate interval for preventive maintenance of the parts of technical equipment. The paper describes a procedure for optimal preventive maintenance for CNC electroerosion equipment Sodick AQ15L when considering Weibull distributions of random variables of failures.