Over-voltage vulnerabilities delivered right to your door

Many PC power supply manufacturers claim in their documentation that they protect against power-overload conditions. Unfortunately, many of them don't protect against over-voltage conditions, which can be even more dangerous.

Overload and over-voltage conditions are two different phenomena, and cheaper power supplies may protect against one but not the other. Power supplies in industrial-grade electrical equipment have a fail-safe called a "crowbar circuit," which shuts off the power supply if the unit's output voltage -- not what goes into it, but what comes out of it and is passed to the PC -- goes beyond safety limits. This keeps the excess output voltage from burning out the power supply itself, or worse, frying the computer it's attached to.

Now the bad news: Some PC power supplies do not have adequate over-voltage protection. In fact, some power supply manufacturers, as a cost-cutting measure, simply omit it, and many users are just not aware that such an omission can be hazardous. Perhaps those manufacturers assume that a customer who is half-savvy about protecting PCs would have conditioned line power, but that's not a guarantee that the system can be protected internally.

If you are building equipment for your organization, Antec Inc., based in Fremont, Calif., puts out some of the best product in this space: Not only does it outfit its power supplies with overload and over-voltage protection, but it also provides detailed feature documentation.

In the U.S., stick with devices that have been put through Underwriters Laboratories Inc. (UL) safety testing; any power supply with the UL logo is certain to have over-voltage protection. Dedicated power supplies, such as the types built for many Compaq (Hewlett-Packard Co.) and Dell Inc. machines, may require that you find stock from the manufacturer rather than replace them with generic units.