[en] Serviceability criterium for superconducting winding wires with washed transition for fabrication of magnet systems is proposed basing on the analysis of maximum total heat release in the system and on a particular temperature assurance above the working point. On the example of winding wire for the T-15 superconducting magnet system (SMS) calculated are the boundary curves in coordinates of critical current-current rate factor for winding wire serviceability. It is shown that the method of analysis of superconducting wire serviceability when its application in SMS with a given power of refrigerator allow one to choose the wire for fabrication in SMS on the basis of results of study on voltage-current characteristic of a short sample. The conclusion is made that the serviceability of wires with washed voltage-current characteristic is restricted by the SMS total heat release, and the wires with sharp transition - by breaking of heat balance in the region of maximum magnetic field. The developed method permits to estimate the wire performance in the region of maximum magnetic field at a given level of thermal disturbances