The part that wears out inside a surge protector
A surge protector does not block electricity the way a switch blocks a current. Its key component, a metal-oxide varistor (MOV), sits between the power-line wires. At ordinary household voltage, it resists the flow of electricity. When voltage briefly rises too high, the MOV becomes conductive and diverts some of that excess energy away from connected equipment.
That response has a cost. The surge heats the MOV, and repeated heating gradually changes how it behaves. A small event may do little; a larger or repeated series of spikes can use up much more of its capacity. The protector can look perfectly normal even as its ability to limit a future surge diminishes.
Why the outlet can keep working
Many protectors are designed so that a worn-out MOV disconnects from the circuit rather than leaving a damaged component connected to the power line. The outlets can still pass ordinary household electricity, but the surge-limiting part may no longer be active. In other designs, failure may affect the device differently, so a working lamp is not proof that protection remains.
Some models have an indicator light that signals whether protection is available. That light is useful only if the model includes it and it is functioning; a power light alone may simply show that the outlet has electricity. Check the product’s instructions to understand what its indicators mean.
The practical consequence is easy to miss: a surge protector can become an ordinary extension cord without looking broken. After a major electrical event, or when its protection indicator says protection has been lost, replace it rather than assuming that a powered-on device is still guarding your electronics.
