Although this article is old, the importance of having proper protection has not changed.

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Power Protection
by T. Zinneman
June 5, 2001

Power disturbances such as electrical outages and brownouts have become commonplace. So have transient voltages and power surges. Any drop or surge in power can not only wipe out your unsaved files, but also permanently damage your computer. You can provide protection for your computer against these disturbances by inserting a power conditioner between your power outlet and your computer system. There are two types of conditioners available for home use: surge suppressors (also called surge protectors) and uninterruptible power supplies.

The simpler, less expensive surge suppressors will remove or minimize voltage spikes and power surges that appear from time-to-time on your incoming ac power lines. In Florida, thunderstorms and the associated lightning strikes are one of the major causes of voltage spikes and surges. These power disturbances can also occur when the power company switches from one source of power to another. Note that surge suppressors provide no protection against power outages or brownouts.

Surge suppressors range in cost from $10 to $100. The least expensive devices usually use only metal-oxide varistors (MOVs) to shunt the voltage spikes to ground. Each incident damages the MOVs, so that eventually the device offers no protection and must be replaced. More expensive devices use additional components, such as gas-discharge capacitors, LC filters, and thermal fuses to provide protection. Most suppressors have an LED that indicates whether they are damaged or not. If the LED is out, the suppressor is probably damaged and should be replaced.

A lot of products are labeled as surge suppressors, but provide very little protection. When selecting a surge suppressor, make sure that it meets or exceeds UL 1449 specifications. A good suppressor should be able to dissipate at least 300 joules of energy before it fails. It should also have a response time of one nanosecond or less and have a clamping voltage of 330 volts or lower.

If your computer is connected to the outside world via a modem, you need telephone line protection. Many surge suppressors include surge-protected RJ-11 jacks through which you can route your telephone line before connecting to your computer's modem. Some models also provide surge-protected coax jacks to protect your system if you use a cable modem or TV tuner card with your PC.

An uninterruptible power supply (UPS) offers a safer form of protection for your computer system. All UPSes contain an internal battery and an inverter. The inverter turns the battery's DC power into AC power, which is suitable for computer equipment. In the event of a power failure, the UPS's internal batteries will continue to provide a steady voltage for several minutes, allowing you to save your data and provide an orderly shutdown. Most units also include protection from surges, spikes, brownouts, and voltage sags. Many include RJ-11 jacks and coax jacks to protect modems. Some can even automatically perform a controlled shutdown of your system.

UPSes come in three basic types: offline, online, and line-interactive. An offline UPS, also called a standby UPS, switches over to batteries only during power outages. The switching interval, about five milliseconds, is brief enough that PCs don't notice the interruption. With an online UPS, all power to the computer system passes through the inverter, whether there's a power failure or not. The power is constantly conditioned to a steady 120 volts, without the dips or spikes inherent when an offline UPS makes the switch from utility power to battery power. The third alternative, the line-interactive, combines elements of the online and offline approaches. Like the online system, the line-interactive UPS keeps its inverter in constant use, but only for charging the batteries. In the event of a power failure, it switches directions and converts the batteries DC power to AC power. As with the offline UPS, there is a dip in the supply of power while the inverter switches modes. Of the three different types, the online unit provides better overall protection for your system.

The most important feature of any UPS is its power rating. It must be large enough to handle the load presented by your hardware. This power rating is usually given in volt-amperes (VAs). Units for home use are typically sized from 200 VA ($100) to 1000VA ($300). These units provide 2 or 3 outlets that are both surge-protected and backed by batteries and 2 or 3 outlets with surge protection only. You usually plug your computer and monitor into the battery-protected outlets and other peripherals, such as printers and scanners into the outlets that only have surge protection.

To determine the power level or VA rating you'll need, multiply the amperage of each piece of equipment that you want protected with battery backup by 120; then total the results. Choose a slightly oversize unit to stretch your battery power during a power outage and too provide for future system or network upgrades. For example, a typical small computer requires about 250 VA and a monitor about 150 VA, giving a total of 400 VA. A 450 VA or 500 VA UPS is adequate for these two pieces of hardware.

Manufacturers of surge suppressors and UPSes include American Power Conversion (www.apcc.com), Belkin (www.belkin.com), Cyber Power Systems (www.cyberpowersystems.com), Opti-UPS (www.opti-ups.com), and Tripp Lite (www.tripplite.com). Many of these manufacturers provide one or two-year warranties on their equipment and provide liability insurance that covers properly connected equipment up to a value of $25,000 or more.

One final note. In addition to your computer, there are many items in your house that contain sensitive components that can be zapped by surges. These include TVs, radios, stereos, microwaves, and garage door openers. You should consider a whole-house surge suppressor, which can be installed by your electrician at the circuit breaker box. These devices typically cost in the neighborhood of $200 to $300.