GE P642 Technical Manual page 248

Chapter 9 - Current Protection Functions P64x
If the setting is too low, the 2nd harmonic blocking may prevent tripping during some internal transformer faults. If
the setting is too high, the blocking may not operate for low levels of inrush current which could result in undesired
tripping of the overcurrent element during the energization period. In general, a setting of 15% to 20% is suitable.
224 P64x-TM-EN-1.3