Dell 4100 User Manual

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Dell 4100 User Manual Manual pdf 106 page image

Maintaining the System C-5Power Source InterruptionsComputer systems are especially sensitive to variationsin voltage supplied by the AC power source. Over-voltage, undervoltage, and transients (or spikes) canerase data from memory or even cause components tofail. To protect against these types of problems, powercables should always be properly grounded and one orboth of the following methods should be used:• Use an uninterruptible power supply (UPS) or one ofthe other power protection devices described in thefollowing section, “Power Protection Devices.”• Place the system on a dedicated power circuit (ratherthan sharing a circuit with other heavy electricalequipment). In general, do not allow the system toshare 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 equipmentBesides these appliances, the greatest threat to a system’ssupply of power are surges or blackouts caused by elec-trical storms. Whenever possible, turn off the computerand any peripherals and unplug them from their powersources during thunderstorms.If a blackout occurs—even a temporary one—while thesystem is turned on, turn off the system immediately anddisconnect it from its power source. Leaving the systemturned on may cause problems when the power isrestored; other appliances left on in the area can createlarge voltage spikes that can damage the system.Power Protection DevicesA number of devices are available that protect againstpower problems, such as power surges, transients, andpower failures. The following subsections describe someof these devices.Surge ProtectorsSurge protectors are available in a variety of types andusually provide a level of protection commensurate withthe cost of the device. Surge protectors prevent voltagespikes, such as those caused during an electrical storm,from entering a system through the AC power source.Surge protectors, however, do not offer protection againstbrownouts, which occur when the voltage drops morethan 20 percent below the normal AC line voltage.Line ConditionersLine conditioners go beyond the overvoltage protectionof surge protectors. Line conditioners keep a computer’sAC power source voltage at a fairly constant level and,therefore, can handle brownouts. Because of this addedprotection, line conditioners cost more than surge protec-tors—up to several hundred dollars. However, thesedevices cannot protect against a complete loss of power.Uninterruptible Power SupplyA UPS offers the most complete protection against varia-tions in power because it uses battery power to keep thesystem running when AC power is lost. The battery ischarged by the AC power while it is available, so onceAC power is lost, the battery can provide power to thesystem for a limited amount of time—from 15 minutes toan hour or so—depending on the UPS system.UPS systems range in price from a few hundred dollars toseveral thousand dollars, with the more expensive unitsallowing you to run larger systems for a longer period oftime when AC power is lost. UPS systems that provideonly 5 minutes of battery power let you conduct anorderly shutdown of the system, but are not intended toprovide continued operation.If you are using the optional redundant power suppliesinstalled in your PowerEdge 4100 system, connect thetwo power supplies to different circuits, if possible.