Power Protection Guide

Power Protection Guide

Choosing a UPS system

In the event of a power disturbance, a UPS system will give you time to safely close documents and shut down your computer.

System type

Off-line or Standby UPS systems feature a battery with a power conversion circuit (inverter) and a switch that senses irregularities in the electric utility. The UPS provides filtered surge-protected AC line power to your computer. However, when the normal AC line voltage goes beyond the UPS tolerance level or the grid experiences a blackout or brownout, the unit switches to battery backup. Standby UPS is appropriate for PCs and workstations.

Line Interactive UPS systems offer enhanced power protection with Automatic Voltage Regulation (AVR), which enables the UPS to manage a wider range of power disturbances. AVR regulates incoming voltage to a safe 110 to 120 volts, keeping systems online through undervoltages (brownouts) and overvoltages without using battery power. In a power outage, AVR switches your computer to battery backup power, which gives you time to save open files and safely power off. Line Interactive UPS is also appropriate for PCs and workstations and is recommended for small office networking.


UPS systems come in a wide range of VA (volt amp) capacities to accommodate PCs and peripherals, such as modems and inkjet printers. You can easily calculate the VA capacity you need by adding the power draw of all the equipment you want connect to the UPS system. If the power draw of your equipment is expressed in amps, multiply that number by your nominal line voltage, which in North America is 120. If the power draw of your equipment is expressed in watts, multiply that number by 1.4.

Once you have calculated the total VA draw of your equipment, select a UPS system that is rated equal to or higher than that total. Standby UPS systems typically are rated 350VA, 500VA, 650VA, 800VA, 1000VA, and 1200VA, for example. Line Interactive UPS models will cover 700VA to 1400VA.


UPS systems can to provide plenty of runtime for all applications, from several minutes to several days. To choose adequate UPS system runtime, compare the total VA capacity your equipment requires against the half- and full-load runtimes of the UPS system. For example, a UPS system with an 850VA rating—without extended runtime capabilities—can typically support 850VA (full load) for 6 minutes or 425VA (half load) for 21 minutes. If you need longer runtime, choose a UPS that accepts additional external battery packs or sily plug in fewer pieces of equipment.


Look for a UPS system with insurance ratings that guarantee your equipment will be protected from surge damage, including direct lightning strikes. Policies that are effective the moment you purchase the surge protector, with no forms to fill out and send in, are the best.


A variety of connectivity options on USB systems lend them flexibility for anyone's needs. Power connections include 15-, 20- and 30-amp receptacles, providing either 120V or 230V power, as well as external battery connectors. In addition, manageability connections include DB9 ports, USB ports, and EPO (Emergency Power Off) ports.


Several useful management functions are available with UPS systems. Standby and basic line-interactive UPS systems can perform orderly unattended system shutdowns during extended blackouts using software included with the system or downloadable for free. Intelligent UPS systems with communication ports allow you to communicate through TCP/IP (a money-saving feature) or via PDAs or Web phones (a convenience feature).


Power Protection
Types of Power Protection
Choosing a Surge Protector
Choosing a UPS system
Power Terms

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