Editing Lightning (section)

==== Discharge – Transient currents during flash ====
The electric current within a typical negative CG lightning discharge rises very quickly to its peak value in 1–10 microseconds, then decays more slowly over 50–200 microseconds. The transient nature of the current within a lightning flash results in several phenomena that need to be addressed in the effective protection of ground-based structures. Rapidly changing (alternating) currents tend to travel on the surface of a conductor, in what is called the [[skin effect]], unlike direct currents, which "flow-through" the entire conductor like water through a hose. Hence, conductors used in the protection of facilities tend to be multi-stranded, with small wires woven together. This increases the total bundle [[surface area]] in inverse proportion to the individual strand radius, for a fixed total [[Cross section (geometry)|cross-sectional area]].

The rapidly changing currents also create [[Electromagnetic pulse|electromagnetic pulses (EMPs)]] that radiate outward from the ionic channel. This is a characteristic of all electrical discharges. The radiated pulses rapidly weaken as their distance from the origin increases. However, if they pass over conductive elements such as power lines, communication lines, or metallic pipes, they may induce a current which travels outward to its termination. The surge current is inversely related to the surge impedance: the higher in impedance, the lower the current.<ref>{{Cite web|url=https://site.ieee.org/sas-pesias/files/2016/03/Lightning-Protection-and-Transient-Overvoltage_Rogerio-Verdolin.pdf|title=Lightning Protection and Transient Overvoltage}}</ref> This is the [[Voltage spike|surge]] that, more often than not, results in the destruction of delicate [[electronics]], [[electrical appliance]]s, or [[electric motor]]s. Devices known as [[Surge protector|surge protectors (SPD) or transient voltage surge suppressors (TVSS)]] attached in parallel with these lines can detect the lightning flash's transient irregular current, and, through alteration of its physical properties, route the spike to an attached [[Electrical ground|earthing ground]], thereby protecting the equipment from damage.