When a power strip stops working, the failure is rarely in the cable, the plug or the copper bar running down its length. It is the little rocker switch. Press it and nothing happens, or it works on the third try. Everything else on the strip is still sound, because everything else is a passive piece of metal or plastic that never moves. The switch is the one part asked to move tens of thousands of times.
Inside that rocker there are two contacts and a spring. When the switch is closed, the spring presses one contact against the other hard enough to keep the contact resistance low, so current passes without much heating. Open it and the contacts separate. That separation is the whole problem: for a moment the current is still flowing across a narrowing gap, and it does so as a small arc.
What one click costs
An arc is hot far out of proportion to its size. Each operation burns a microscopic amount of material off the contact face, leaving a pit and a little oxidation. One click is nothing. Thousands of clicks roughen the surface, and a rough surface meets at fewer points, which raises the resistance at exactly the place that must stay cool. Contact makers use silver alloy faces and a wiping action — the contacts slide slightly as they close — to clear that film and spread the wear.
The spring has its own slow failure. It is a thin piece of metal held under tension, and it lives next to a conductor carrying current. Sustained warmth gradually relaxes it. As the contact pressure drops, resistance rises; higher resistance produces more heat; more heat relaxes the spring further. This is a loop that feeds itself, which is why a switch that has begun to feel sloppy tends to get worse steadily rather than failing all at once.
Load matters as much as the number of clicks. A motor or a compressor draws several times its running current for the first fraction of a second, and a charger with a capacitor bank draws a brief charging surge when it is plugged in. Switching either on is harder on the contacts than switching a lamp. Two identical strips, used for the same number of clicks on different appliances, will not age at the same rate. The same thermal story appears in an LED bulb, where the driver capacitor fails before the chip, and in a kettle where one switch is designed never to operate.
Why the rest of the strip survives
A copper bar is a solid conductor with no relative motion, so it has almost nothing to wear. The shell is moulded with ribs and rounded corners that let it leave the tool cleanly, and once it is out of the mould its job is simply to hold shape. Even a protective element in a surge-protected strip is a static component that degrades only when it absorbs an event. The rocker is the only subassembly with a specified mechanical life, so it is the natural place for a service life to end.
Design responds in predictable ways: a contact alloy that resists pitting, a spring with enough travel to stay in its elastic range, a switch position where heat can leave, and a housing that keeps the rocker from being pressed at an angle. Safety rules set limits on temperature rise at the terminals, which indirectly sets a floor under how good that contact has to be. None of it changes the basic asymmetry — one moving part among many static ones.
You can read the decline without opening anything. A click that has gone soft and dull, a rocker that no longer returns crisply, or a patch of warmth on the housing right over the switch all point to falling contact pressure. At that stage the strip is still conducting, just less well, and the loop is already running. The plastic, the bar and the cable would have kept going for years; the part that had to move is the one that decided otherwise.