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When lightning strikes enormous amounts of energy are dissipated. If the strike is in any way direct or near direct then most substances hit will be locally vapourised. Electrical distribution systems have special isolating devices to restrict the effects of lightning strikes on overhead wires. However overhead lines can pick up serious transients which will destroy sensitive electronics if the `spike' gets all the way into the equipment.
A typical lightning strike produces a waveshape which has a front edge of about 1.2µS and after 50µS the voltage will have dropped to half its peak value. Special test equipment is available which generates a 8/20 µS waveform which represents the lightning effect if the voltage is 6kV and the source impedance less than 2 ohms. A further popular test is based on a 10/350 shape which is used in telecoms applications.
It is not generally appreciated that office and domestic electrical distribution wiring will normally `flash over' at about 6kV which limits the voltage expectation from local lightning strikes.
A typical `strike' may carry about 200 000 Amps which when applied to an earthed conductor will cause a huge rise in the local earth potential. This effect can cause quite large amounts of energy to be carried along local earth wiring. Particular attention needs to be given to this problem. See ICT wiring and considerations.
Advance CVTs especially designed for computer protection provide one of the most effective barriers against lightning damage. The CVT has a magnetic circuit which becomes a very low impedance when fed with high voltage.
If the unit is correctly installed with a protecting fuse or circuit breaker then the CVT will blow the fuse/breaker before damaging energy gets to the electronic equipment being protected.
This means that the computer or other equipment may be turned off inadvertently but it will be protected from the resulting distributed energy from the lightning strike. Such energy spikes are relatively common.
The only user action required is to replace the fuse or reset the circuit breaker and continue using the equipment.
If the strike is of sufficient energy to damage the incoming distribution wiring because of a direct strike then anything may happen.
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