OMEGA ELECTRONICS
6904 West Fairfield Dr
Pensacola, Fl. 32506-3310
Re: Failure of electronic equipment with regards to AC power/lightning
To whom it may concern:
Severe power line voltage increases may result from lightning strikes,
heavy equipment cycling on or off, or unexpected power line transformer
switching or failure. These types of voltage increases are normally
momentary in nature and produce spikes that last from
nanoseconds (billionths) to milliseconds (thousandths). Spikes are stopped
by components like transformers and coils. These components
are normally in the power supplies of the equipment. However they usually
have low value by-pass capacitors in parallel with them.
Capacitors, especially low value ones, are actually designed to pass high
frequency AC. Frequency is the reciprocal of time, hence short
time (nano or milliseconds) is equal to high frequency, the result being a
coupling of the spike into the equipment. These spikes are
then normally reduced by other components in the circuit. The key word
being normally. Power line voltage increases that contain high power
levels (joules) dissipate a great deal of heat and can do extensive
damage, burning boards, wires, components, or starting fires. Lightning
strikes contain a great deal of power but only last for a short time so
catastrophic failure of electronic equipment seldom starts fires but
may blow parts off the board. Increases in power line voltage that last
for long periods of time (seconds) usually do the same type of
damage even though the energy is less; but because the increased voltage
is applied longer the components may heat to the same level.
Transients sometimes have unpredictable effects. Although arcing from one
conductor to another dissipates a great deal of energy it may
not reduce the spike to a level acceptable by the equipment. And it may
couple the current into an otherwise disconnected piece of equipment. A
spike coupled into a piece of equipment may cause the failure of a
sensitive component well past the "normal" area where a failure would
occur from a "strike". In short, an "abnormal" failure can not reliably
be said to not be caused by power line aberrations.
Wayne Vanaman, owner, technician
01/27/2006