theTVsetwhenavacuumcleanerisoperatedonthesameelectricalcircuit.Thestaticyou
hear is electrical noise. Nearby electrical storm can also be picked up by the electric sup-
ply and transmits EMI over the supply lines.
Nearly all PC power supplies are built to handle normal levels of line noise, but exces-
sive line noise often passes through the power supply to the motherboard, disk drives,
and any other devices connected to the power supply. Line noise can cause serious prob-
lemsforaPCoraserverifitisnotprotected.Thetypesofproblemsthatcandevelopfrom
electrical line noise include memory errors, data loss, circuit connection loss, data trans-
mission problems, and frequent system lockups.Power Surges
The nominal operating voltage of the AC (alternating current) electricity supplied to the
wall outlets in your house or office is 110 volts, and that’s what the power company will
tell you is the voltage of your wall outlets. However, in real life, the actual voltage on the
line can vary between 85 and 135 volts, and most PC power supplies have a strong
enough operating range to handle power fluctuations within a certain range. Most ATX
form factor power supplies (see Chapter 14 for more information on the PC power sup-
ply) have operating ranges like 92 to 130 volts AC or 90 to 135 volts. Systems designed to
operateon220voltsACorthatcanbeswitchedbetween110-voltserviceand220-voltser-
vice typically have an operating range of 180 to 270 volts AC.
Certain disturbances in the area, such as a lightning storm, distant lightning strikes,
or problems on the electrical power supply grid such as a major factory shutting down all
at once or a sudden drop in the load on the supply lines can cause the voltage on the line
to suddenly increase. This shar pincrease of voltage is an over-voltage event called a
surge. An electrical surge is a temporary increase of voltage on the line. A surge is like a
rogue wave of electricity that can increase the voltage to as much as 1,000 volts. It typi-
cally does this for only a few thousandths of a second, but that’s plenty of time to damage
anything in its path. Power surges are very common when the power returns from a
blackout (see “Blackouts” a little later in this section).
PC power supplies are designed to withstand voltage surges to certain levels, and
most are subjected to a few a year. However, even the best power supply will begin to
lose its ability to withstand a power surge and can in time begin to fail or begin passing
the surge on to internal PC devices connected to it. It is also common for power surges to
happen in clusters, which can be fatal for an unprotected system.Power Spikes
A power spike is a sudden, usually one-time, extremely high-voltage peak of over-voltage
on the electrical line. A typical cause of a power spike is lightning striking within a few
miles of your vicinity. Lightning carries millions of volts, and if your home or office takes a
direct hit, your PC is very likely to be heavily damaged, right along with everything else
electrical in the building. Lightning directly striking a building is a fairly rare event, but
even a strike within several miles can create an electrical current in metal objects near theChapter 23: Electrical Power Issues^601