Keraunic level

The keraunic level describes the lightning and thunder acivity in a given area. It is defined as the annual number of days where thunder can be heard. This number in some areas will vary a lot, and the keraunic level is the long-term average. In temperate regions the value is 10 to 30; in the African rainforest values exceeding 180 can be reached. The annual number of lightning flashes hitting one square km of ground, "N_g", can for temperate regions be calculated from following formula:

:$N\_g\; =\; 0.04,\{T\_d\}^\{1.25\}$

where T_d is the keraunic level.

In application, the keraunic level has been used to set standards for safe design of electrical systems in structures connected to the local power grid.

Sources: BS 7671:2001, EN61400-24, IEC 60664-1