Power Source Interruptions; Power Protection Devices; Surge Protectors; Line Conditioners - Dell 4100 User Manual

Power Source Interruptions

Computer systems are especially sensitive to variations
in voltage supplied by the AC power source. Over-
voltage, undervoltage, and transients (or spikes) can
erase data from memory or even cause components to
fail. To protect against these types of problems, power
cables should always be properly grounded and one or
both of the following methods should be used:
•
Use an uninterruptible power supply (UPS) or one of
the other power protection devices described in the
following section, "Power Protection Devices."
•
Place the system on a dedicated power circuit (rather
than sharing a circuit with other heavy electrical
equipment). In general, do not allow the system to
share a circuit with any of the following:
— Copier machines
— Air conditioners
— Vacuum cleaners
— Space heaters
— Power tools
— Teletype machines
— Adding machines
— Laser printers
— Facsimile machines
— Any other motorized equipment
Besides these appliances, the greatest threat to a system's
supply of power are surges or blackouts caused by elec-
trical storms. Whenever possible, turn off the computer
and any peripherals and unplug them from their power
sources during thunderstorms.
If a blackout occurs—even a temporary one—while the
system is turned on, turn off the system immediately and
disconnect it from its power source. Leaving the system
turned on may cause problems when the power is
restored; other appliances left on in the area can create
large voltage spikes that can damage the system.
P
ower Protection Devices
A number of devices are available that protect against
power problems, such as power surges, transients, and
power failures. The following subsections describe some
of these devices.

Surge Protectors

Surge protectors are available in a variety of types and
usually provide a level of protection commensurate with
the cost of the device. Surge protectors prevent voltage
spikes, such as those caused during an electrical storm,
from entering a system through the AC power source.
Surge protectors, however, do not offer protection against
brownouts, which occur when the voltage drops more
than 20 percent below the normal AC line voltage.

Line Conditioners

Line conditioners go beyond the overvoltage protection
of surge protectors. Line conditioners keep a computer's
AC power source voltage at a fairly constant level and,
therefore, can handle brownouts. Because of this added
protection, line conditioners cost more than surge protec-
tors—up to several hundred dollars. However, these
devices cannot protect against a complete loss of power.

Uninterruptible Power Supply

A UPS offers the most complete protection against varia-
tions in power because it uses battery power to keep the
system running when AC power is lost. The battery is
charged by the AC power while it is available, so once
AC power is lost, the battery can provide power to the
system for a limited amount of time—from 15 minutes to
an hour or so—depending on the UPS system.
UPS systems range in price from a few hundred dollars to
several thousand dollars, with the more expensive units
allowing you to run larger systems for a longer period of
time when AC power is lost. UPS systems that provide
only 5 minutes of battery power let you conduct an
orderly shutdown of the system, but are not intended to
provide continued operation.
If you are using the optional redundant power supplies
installed in your PowerEdge 4100 system, connect the
two power supplies to different circuits, if possible.
Maintaining the System C-5