Dell PowerVault 220S (SCSI) - Manual (Page 11)

Introduction: Dell PowerVault 220S and 221S Systems User's Guide
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Preventing Unauthorized Access to the System
The PowerVault 220S can be secured with the lock on the rack door. The PowerVault 221S has a keylock mechanism on the
top of the front bezel that prevents unauthorized access to the system.
Power Protection Devices
A number of devices are available to 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 electrical outlet. 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—up to several hundred dollars. 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 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. Surge
protectors should be used with all UPS systems, and the UPS system should be Underwriters Laboratories (UL) safety-
approved.