Online calculator of induced voltage into wire loop by a lightning

With this online calculator you can estimate the need of your external lightning protection and internal lightning protection like SPDs (surge protection device).

The strings of a photovoltaic-system builds a wire loop, which is unfortunately a good situation for a induced voltage by a lightning into the strings.

The below formula calculates the maximum voltage you get, when the magnetic flow goes orthogonal through the loop. So the maximum induced voltage you get if the lightning is parallel to your strings. This can indeed happen, when the lightning goes through a gutter or lightning rod on the roof.

Please play around with the distance of the wires. You will see: keep the distance between the wires as small as possible! Have fun! 

Distance to lightning (in m)

Length of the string (in m)

Average distance of the wires (in cm)

Amperage of lightning (in kA)        

Rise time of Amperage (in us)         



Derivation and Sources

I used the formulas, which are derived in this nice paper:

Calculation of induced Voltage:

Calculation of maximum currency if short-circuited:

with Ls as:


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