In the standard procedures for high-power short-circuit testing of current-limiting fuses, the test circuit is conventionally characterised by the RMS test voltage, prospective current, frequency, closing angle, and power factor. From these parameters a constantRLequivalent circuit can be derived, which has been widely used in the modelling of fuse-breaking transients, but recent studies have shown that this circuit model is inadequate. The frequency dependence ofRandLhas been investigated by fast-Fourier-transform analysis of fuse-breaking test transients obtained in a high-power short-circuit test laboratory, and the results show that, whileLdecreases slightly,Rincreases greatly with frequency. The nominal-power-factor value provides only a measure of the DC resistance of the circuit. The frequency dependence ofRmust be taken into account for accurate modelling of the operation of current-limiting fuses.