What Causes Surge
Surge sources fall into two families: natural events dominated by lightning, and man-made events dominated by something inductive being switched off. Both inject energy the same way -- a collapsing magnetic field or an ionized air gap forcing current somewhere it wasn't flowing a moment ago.
Select a natural source below to see how it couples energy onto power and signal networks.
Virtually every man-made surge source shares one mechanism: an inductive load (a motor winding, a transformer, a relay coil, a cable's own inductance) carrying current has that current interrupted abruptly. Since an inductor resists any sudden change in current, the collapsing magnetic field forces a large voltage spike across the open switch contacts to keep current flowing for a few more microseconds.
Illustrative comparison of typical peak surge energy delivered to an unprotected 230 V mains interface, by source category.
Module 2 Quiz
Select the best answer for each question. Instant feedback is provided after each response.