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I have been looking at UPS's and noticed that they usually have a joules rating much lower than what a relatively inexpensive $40 surge suppressor does. Does this mean that in the event of a surge that the more expensive UPS is in fact not giving me as much protection?

Or, as I suspect, that a UPS is a bit of a different field and therefore I'm not comparing apples to apples?

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up vote 3 down vote accepted

In the event of a surge the UPS switches from mains to battery, so the suppression is only needed during the brief moment before it switches. A surge suppressor must bear the brunt of the surge for the entire duration. Joules is Watts times seconds, so the longer the surge must be suppressed, the higher the rating must be.

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The number measured in "joules" is the amount of energy the suppressor can dissipate safely. There are other factors to consider (like response time and "clamping voltage" - the minimum voltage at which a surge of current will be directed to ground). So it may be that the joule rating does not say everything about a product.

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