strike. This means that any wires or cables in the area can pick up an electrical spike and
pass it to whatever is connected to it. The wire or cable could be a power cable on a PC, a
telephone wire, the electricity supply to a house or building, and so on. The chances are
slim that your home or office will be directly struck by lightning any time soon, but the
odds of a lightning strike near you are pretty good.Power Sags or Dips
Sudden demands for power on the power grid can create a wave of low-voltage on the
electrical supply system, which is called a sag or a dip. As the name suggests, a power sag
is the opposite of a power surge—it’s a temporary dip in the voltage on the supply line
thatusuallylastsonlyafractionofasecond.Powersagsthatextendbelowthenormalop-
erating voltage range of a system are rare, but they can happen.
Most of the components in the PC are not designed to operate at very low voltages,
even for a very short time. The PC’s power supply has some power in reserve to pull up
short power sags. However, a series of power sags in a short time can affect the power
supply’s ability to provide the correct voltages to internal PC components and could
weaken, damage, or destroy them.Brownouts
When the demand for electrical power exceeds the capability of the electrical supply sys-
tem, the result is reduced voltage for everyone, or what is called a brownout. Brownout is
meant to indicate that while there is enough power on the grid to prevent a blackout, or a
total loss of power, there isn’t enough power to meet the current demand. Brownouts fre-
quently occur during extreme weather conditions, such as a sudden abnormally cold or
hot spell, when everyone is running their heat or air conditioning.
A brownout is when the voltage on the electrical supply circuit is less than 105 volts
AC for an extended time, which could be minutes or hours. A brownout strains the PC in
the same way as a power sag, but because a brownout lasts longer, the result can be im-
mediate failure of some components, a burned out power supply, or in an extreme case,
the corruption or loss of data. Brownouts are a tool employed by the power companies to
shift supply around the grid to meet the demands in specific areas on a rolling basis, or
what is called rolling brownouts, and the damage to a PC is often not noticed right away.
However,thestrainonaPC’scomponentsaccumulatesandeventuallyresultsinafailure
that is nearly impossible to troubleshoot. Brownouts are far harder on computer equip-
ment than blackouts.Blackouts
A blackout is a complete loss of a PC’s electrical source. Typically, you think of a black-
out as a failure of the power supply grid over an entire area, but a blackout can occur in
just a part of a building, an entire building, a block, a section of a city, or an even larger
area. A blackout event is a sudden complete drop-off of the power source, which can(^602) PC Hardware: A Beginner’s Guide