Dell PowerEdge 6400 - Manual (Page 45)

Power Source Interruptions
Systems are especially sensitive to variations in voltage supplied by the AC power source. Overvoltage, 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:
l Use one of the power protection devices described in the following section, "Power Protection Devices."
l 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 threats to a system's supply of power are surges or blackouts caused by electrical storms. Whenever
possible, turn off the system and any peripherals and unplug them from their electrical outlets 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 electrical
outlet. Leaving the system on may cause problems when the power is restored; all other appliances left on in the area can create large voltage
spikes that can damage the system.
Power 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 level.
Line Conditioners
Line conditioners go beyond the overvoltage protection of surge protectors. Line conditioners keep a system'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 protectors.
However, these devices cannot protect against a complete loss of power.
Uninterruptible Power Supplies
Uninterruptible power supply (UPS) systems offer the most complete protection against variations in power because they use 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 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. Surge protectors should be used with all UPS systems, and the UPS system should be Underwriters Laboratories (UL)
safety-approved.
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