Walk down the electrical aisle of any hardware store and you'll see two products that look nearly identical: a row of outlets on a plastic bar, a cord, a little switch that glows when it's on. One of them costs eight dollars and the other costs thirty, and the packaging isn't always in a hurry to explain why. The difference matters more than the shelf placement suggests, because one of these products protects the electronics plugged into it and the other protects absolutely nothing. I owned three of the eight-dollar kind for years under the confident assumption that they were "surge protectors," and I was wrong about all three.
Six outlets is not protection
A basic power strip does exactly one job: it turns one wall outlet into several. Inside the housing there's little more than a set of metal strips connecting the outlets to the cord, plus the switch. On many strips that switch doubles as a small circuit breaker, which sounds reassuring until you understand what it actually does — it cuts power if the strip as a whole is asked to carry more current than it's rated for. That's overload protection for the strip itself, the same job your panel's breaker does for the circuit. It has nothing to do with surges.
So when a voltage spike comes down the line, a plain power strip passes it straight through to everything plugged into it, faithfully and instantly. The strip is fine afterward. Your electronics may not be. Nothing about a power strip is defective in this scenario — it simply was never built to notice voltage at all, only current.
What a surge actually is
Household power in North America arrives at a nominal 120 volts, and your devices are built around that assumption. A surge is a brief spike above that level — sometimes lasting only microseconds — that rides in on the wiring. The dramatic cause everyone pictures is lightning striking nearby, and that does happen, but it's the rare case. Far more common are small surges generated by the electric utility switching loads around the grid, and — most common of all — spikes generated inside your own home, every time a device with a big motor cycles on or off. Your air conditioner's compressor, your refrigerator, a sump pump: each cycle can kick a small voltage spike back into the house wiring.
A single small surge won't visibly hurt anything. The problem is accumulation — those little spikes stress the components in electronics a tiny bit at a time, which is one reason devices sometimes just quietly die years before they should. The big lightning-adjacent surge is a knockout punch; the daily household surges are more like rust.
What's inside a real surge protector
A surge protector looks like a power strip from the outside, but inside it carries extra components — most commonly small discs called metal oxide varistors, or MOVs — wired between the power lines and ground. Under normal voltage, an MOV is effectively invisible; current flows past it to your outlets as if it weren't there. But when voltage spikes past a designed threshold, the MOV suddenly becomes an easy path, and the excess energy gets diverted away from your devices instead of through them.
The key word for that threshold is the clamping level — the voltage at which the protector starts diverting. The protector doesn't block the surge like a wall; it shaves off everything above the clamping level and lets normal power keep flowing underneath. That's also why this is called "clamping" rather than "switching off": your devices never lose power during the event. Ideally they never notice it happened at all.
What the joule rating actually tells you
Every time an MOV clamps a spike, it absorbs energy — and MOVs are sacrificial parts. Each clamping event burns up a little of their capacity, and a big event can burn up a lot of it at once. The joule rating printed on the package is the total energy budget the protector can absorb over its whole life before its protection is effectively gone. A 200-joule unit might be spent after one modest event; a 2,000-joule unit has far more headroom for both the daily trickle of small surges and the occasional big one.
The little light matters more than the outlet count
Because a spent surge protector keeps working perfectly well as a power strip, manufacturers add a small indicator light — usually labeled something like "protected" or "protection working" — wired to report whether the MOVs are still functional. When that light goes dark, the protector has retired itself without telling you any other way. It will happily keep powering your television for another decade while protecting it from nothing.
That light is the single most useful thing on the device, and it's worth glancing at the way you'd glance at a smoke detector's blinking LED. Some better units go a step further and cut power entirely once protection fails, which converts the silent failure into an obvious one — a design choice I appreciate, since a dead outlet gets investigated and a dark indicator light mostly doesn't.
When whole-home protection is the better answer
Plug-in protectors defend one outlet's worth of devices at a time, which leaves an obvious gap: the appliances that never touch a power strip. Your HVAC system, oven, well pump, garage door opener, and everything else wired directly or plugged in behind heavy furniture are all exposed to the same surges your TV is. A whole-home surge protector addresses this differently — it's a device mounted at the electrical panel that clamps surges at the point where power enters the house, protecting every circuit at once. Plug-in units then act as a second layer for sensitive electronics, catching what gets past the first.
Sorting out what's on your floor right now
If you're now squinting suspiciously at the strip behind your desk, the packaging-free way to identify it goes like this. Look for a joule rating printed on the underside or the plug end — a genuine surge protector almost always advertises this number somewhere on the device itself, and a plain power strip has nothing to advertise. Look for the words "surge protective device" or a reference to the UL 1449 safety standard on the label, which is the wording real protectors carry. And look for an indicator light beyond the simple power switch — a "protected" light only exists on units that have protection to report on.
If the device has an indicator light and it's dark, treat the unit as a plain strip and replace it if you want protection back. If a serious electrical storm has passed close by since you bought it, treat the joule budget as suspect even if the light is still on — indicator circuits report total failure, not a budget running low. And if the thing has no joule number, no standard markings, and no protection light anywhere on it, the mystery is solved: it was never a surge protector to begin with, no matter what the person who bought it — possibly me, possibly you — believed at the time.