Perhaps there is a flat box sitting under your monitor with many switches on it, or perhaps there is a power strip on the floor... Beware! These plug-in devices might or might not be a surge protector!

How do you tell?

There exist a set of standards to which products and components have been tested. These standards, defined by the Underwriter's Laboratory (UL), are numbered and will appear on the product if the product or its component has passed scrutiny.

For surge protection - look for UL1449. This states that the product is certified as a 'Transient Voltage Surge Suppresser' and that it has a Let-Through voltage rating of no more than 330 volts. This is also referred to as Clamping Voltage.

Other points to look for in surge protection include:

RESPONSE or CLAMPING TIME - this is the time for the product to react - look for nano (billionths) or, even better, pico (trillionths) of seconds.

JOULE RATING - the measurement of how much damaging energy the unit can handle before the unit becomes impaired - look for a rating above 200-300 joules.

PEAK AMPS - another energy absorbing rating, this measuring the peak surge current, the force behind the voltage - the higher the better - especially for lightning coverage.

TELEPHONE LINE PROTECTION - URL497A - protection for the phone line.

NOISE ATTENUATION - URL1283 - EMI and RFI are disruptions of the smooth AC power-line sine-wave. They can come from distant storms or local appliances.

Just because a product has UL or "UL-listed" on its package does not always mean it is a genuine surge protector. Some manufacturers misrepresent their products. They can claim a UL rating for their products if they use a single UL listed component. "UL-listed" means a product has been submitted to Underwriter's Labs for safety testing in a certain product category, perhaps in the extension cord category. Other products have never been tested as anything more than a Temporary Power Tap, an extension cord. Remember that some vendors rate surge protection on the basis of joule energy alone. These ratings can be misleading. Instead, compare the surge Let-Through voltage measure.

Thanks to, and Consumer Reports Nov 1994 for the information in this article.