Hardware Reference
In-Depth Information
Many cables sold these days are shielded, which means they have a special wrapping that
minimizes EMI interference. Buying shielded cables, although more expensive, can help
greatly with EMI problems.
EMI problems caused by external sources, such as power lines, can be diffi cult to solve;
sometimes moving the devices to a different area in the room or building can help.
Surge Suppressors
Electrical devices rely on the power coming from the wall outlet to maintain a certain
well-defi ned voltage range. However, the actual range may differ because of problems with
the local electricity provider, wiring in the home or offi ce, or environmental conditions.
Sometimes there are outages, power surges or spikes, or sags, any of which can infl ict
major damage to a PC's power supply.
A
surge
and a
spike
are basically the same thing: too much voltage. The term
spike
is
used to describe a more dramatic surge. A
sag,
sometimes called a
brownout,
is insuffi cient
voltage. An occasional power surge can be the result of poor electrical service, but the really
damaging power spikes almost always come from lightning strikes during extreme storms.
External devices can help compensate for the various failings of household and offi ce
electricity. The most basic of these is a surge suppressor. A
surge suppressor
, also called a
surge protector
, is basically an extension cord, but inside it is a metal oxide variable resistor
(
varistor
), sometimes abbreviated MOV, which can absorb any excess power during a surge
or spike, preventing it from reaching the plugged-in devices. The varistor works by depleting
its own ability to resist, so over time a surge suppressor loses its effectiveness in protecting the
PC from power overage. With an inexpensive model, there is no way of gauging the hits
the suppressor has taken or the remaining effectiveness. Some of the better models have
lights that indicate the surge suppressor's “ready” status, like the one shown in Figure 5.5.
FIGURE 5.5
Surgesuppressor
Courtesy of APC
