Transients can arise internally, from normal circuit operations, or externally from the environment. The latter is particularly frustrating because the transient characteristics are undefined. A statistical description can apply though but greater or smaller stresses are possible. The natural frequencies and impedance of indoor ac wiring result in damped oscillatory surges with typical frequencies ranging from 30 kHz to 1.5 MHz. Surge amplitude depends on both the wiring and the source of the surge energy.
Disturbances die out further away from the source.
Transients closer to the service entrance, or in heavy wiring, have higher amplitudes, longer durations, and more damping because of the lower inductance at those locations. Click here for complete article in .pdf format.