scope:

This specification covers the general requirements for power-type, wire-wound, fixed resistors which utilize the principle of heat dissipation through a metal mounting surface. The resistors have an initial resistance tolerance of ±1 percent. These resisors are suitable for continuous full load operation at an ambient tempersture of 25° C, and when derated up to 275° C. However, these resistors should not be used in circuits where their ac performance is of critical importance in the operation of such circuits. The resistors will have life failure rate levels ranging from 1.0 to 0.001 percent per 1,000 hours. These failure rate levels are established at a 60-percent confidence level on the basis of life test. The failure rate level, identified by the appropriate symbol, is referred to operation at full rated wattage at 25° C, with a permissible change in resistance of ±2 percent as the criteria for failure.