|numeral designation defining a classification of transient overvoltage conditions
(Source: IEC 60664-1)
NOTE 1 See 220.127.116.11.2 for a description of the four overvoltage categories.
NOTE 2 A transient overvoltage is defined as a ‘short duration overvoltage of a few milliseconds or less, oscillatory or non-oscillatory, usually highly damped’ [IEV 604-03-13]. It should not be confused with a temporary overvoltage (swell), which is defined as a ‘power frequency overvoltage of relatively long duration’
(Source: IEV 616-01-16)