Fuses for resistance welding machines

CHARACTERISTICS of fuses generally are given by curves in which overload current is plotted against the time required to blow the fuse. This relationship is necessary for most applications, but where the fuses are called upon to protect a device which is recurringly overloaded and unloaded, the characteristics are not useful. Examples of a recurring load exist in the resistance welding field where the welding machine draws up to four to five times its thermal rating during the welding period. Rating sheets for welders and ignitron tubes used with welders can best be expressed in terms of current and duty cycle. Since the welding industry is acquainted with rating sheets of this type, it is desirable to have rating sheets for fuses used in this industry expressed in the same terms.