Hardware Reference
In-Depth Information
precautions to ensure that your PC is not damaged. Refer to
Chapter 18
and
Chapter 19
,
“
Building or Upgrading Systems
,” for more information on ESD.
Static discharges outside a system-unit chassis are rarely a source of permanent problems
within the system. Usually, the worst possible effect of a static discharge to the case, key-
board, or even a location near the computer is a system lockup. Most static-sensitivity
problems are caused by improper grounding of the system power. Be sure you always use
a three-prong, grounded power cord plugged in to a properly grounded outlet. If you are
unsureabout the outlet, youcan buyanoutlet tester,suchasthose described earlier inthis
chapter, at most electronics supply or hardware stores for only a few dollars.
Power-Line Noise
Torunproperly,acomputersystemrequiresasteadysupplyofclean,noise-freepower.In
someinstallations,however,thepowerlineservingthecomputeralsoservesheavyequip-
ment, and the voltage variations resulting from the on/off cycling of this equipment can
cause problems for the computer. Certain types of equipment on the same power line also
cancausevoltagespikes—short,transientsignalsofsometimes1,000Vormore—thatcan
physicallydamageacomputer.Althoughthesespikesarerare,theycanbecrippling.Even
a dedicated electrical circuit used by only a single computer can experience spikes and
transients, depending on the quality of the power supplied to the building or circuit.
During the site-preparation phase of a system installation, you should be aware of these
factors to ensure a steady supply of clean power:
• If possible, the computer system should be on its own circuit with its own circuit
breaker. This setup does not guarantee freedom from interference, but it helps.
• The circuit should be checked for a good, low-resistance ground, proper line voltage,
freedom from interference, and freedom from brownouts (voltage dips).
• A three-wire circuit is a must, but some people substitute grounding-plug adapters
to adapt a grounded plug to a two-wire socket. This setup is not recommended; the
ground is there for a reason.
• Power-line noise problems increase with the resistance of the circuit, which is a func-
tion of wire size and length. So, to decrease resistance, avoid extension cords unless
absolutely necessary, and then use only heavy-duty extension cords.
• Inevitably, you will want to plug in other equipment later. Plan ahead to avoid the
temptation to connect too many items to a single outlet. If possible, provide a separate
power circuit for non-computer-related devices.
Air conditioners, coffee makers, copy machines, laser printers, space heaters, vacuum
cleaners,andpowertoolsaresomeoftheworstcorruptersofaPCsystem'spower.Anyof
