Energy deposition

The time integral of the power dissipated in a clamping type surge protective device during a current surge of a specified waveform.

Comment: The energy deposition is commonly used as a measure of the stress imposed on an SPD. Most varistor manufacturers quote the energy ratings of their devices for a specific waveform, typically 10/1000 ps rather than the 8/20 us, and as a maximum single pulse rating. This rating is generally conservative. Nevertheless, energy computations during evaluation tests should yield results that are well below the ratings to make provision for a long life with multiple strokes (see 'pulse life' in this glossary and Darveniza, 1997 1E.71). There are other parameters for defining the capability of an SPD to handle current surges (with steep front, with very long duration, etc.). The 'joule rating' of an SPD, however, should not be used as sole criterion to compare devices.

Source: UIE Guide to Quality of Electriical Supply for Industrial Installations, Part VI: Transient and Temporary Overvoltages and Currents