Validity of I2T extrapolation of damaging fault currents in metering devices

The use of I²T to extrapolate data points of watthour meter destructive failure tests over a wide range of fault durations is questioned. Data from an experiment using special test fixtures designed for ease of calculation of the electromechanical forces associated with fault currents is discussed for faults to failure having different current magnitudes and durations. High-current-short-duration faults required significantly lower I²T levels to produce a given failure mode than did low-current-long-duration faults. Several failure modes are defined. Confirming tests were made with modern single-phase watt-hour meters.