A surge protector is a power strip or outlet device that limits brief voltage spikes by diverting excess energy away from connected equipment. Most use metal oxide varistors (MOVs) that conduct when voltage rises above a threshold.
Why it matters
Spikes come from lightning, switching of large motors, or utility faults, and can damage power supplies and other electronics. Protection is not permanent: each large surge degrades the MOVs, and a protector can silently stop protecting while still delivering power. Many have an indicator light that shows whether protection is still active.
The joule rating describes how much energy the unit can absorb over its life; a higher number generally means longer protection. Also look at clamping voltage, where a lower figure is better, and response time. Real certification marks, such as UL 1449 in the United States, show the product was tested, though standards vary by country.
Example
A basic power strip has switches and sockets but no protection. A surge-rated strip says so, lists joules, and carries a test mark. Plugging a surge protector into another surge protector adds nothing and can create risks.
Common mistakes
- Assuming any power strip is a surge protector.
- Using one for years after a big storm without checking the indicator.
- Expecting protection from a long power outage or low voltage, which needs a UPS.
- Overloading a strip with heaters or other high-wattage appliances.
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This page is general information written by our editorial team and updated when documentation changes. Servers and providers differ, so test changes safely first. See our editorial policy and disclaimer.