Computers, once they're running, like to remain running.

They hate sudden power interruptions.
In South Florida. unfortunately, sudden power interruptions are part of our daily summer thunderstorms.

Sudden power interruptions can damage computer hard drives and other components.

Enter the UPS

If you value your computers and their data, protect them from damage by placing a UPS (Uninterruptible Power Supply) in each computer's power supply line. A UPS contains a rechargeable battery that's trickle charged by the 110 Volt AC power from a wall socket most of the time. When your 110 Volt AC power fails, the battery within the UPS is used to supply AC power to your computer. Typical maximum run times range from a few minutes to an hour or more. For a given UPS, the AC power out runtime is inversely proportional to the load.

UPS and voltage regulator in one box

Traditionally, a line-interactive UPS (illustrated below) uses an autotransformer to regulate its output voltage to compensate for wide voltage swings by the electric power utility:

Line interactive UPS

Most UPSs don't provide voltage regulation -- they just provide emergency backup power. If your electric power is both unreliable and suffers wide voltage swings, you need a line-interactive UPS. Otherwise, a relatively simple standby UPS will work fine.

Most off-the-shelf UPSs

This illustrates a "standby" UPS -- the inverter doesn't run except when the power fails. Most UPSs are of this type:

Standby UPS Diagram

Which UPSs do I recommend?

I prefer UPSs that are made by APC (American Power Conversion). I like their "Smart-UPS" line because they include an interface cable and Powerchute software so that your PC or server can monitor the status of the UPS battery; the UPS will notify the computer's Powerchute program (via a USB or RS-232 cable from the UPS to the computer) before the battery voltage drops too low; then Powerchute will gracefully close any open files and shutdown your computer just as you do now from the keyboard. It does this while unattended.

If your budget doesn't allow a Smart-UPS at every workstation, a simple APC Backup-UPS (which has no Powerchute management capability) is better than nothing!

Keep systems running after UPS batteries are depleted: