While some surge protectors will completely stop working after they no longer provide surge protection, many silently continue to function as a power strip while leaving your devices open to electrical surges. Surge protectors with higher joule ratings will last longer and protect from more intense surges, but even high-end protectors need replacement after they absorb their rated amount of electricity.
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How Surge Protectors Work
Electrical surges can occur due to turning large appliances on or off, or from external factors such as lightning. Surge protectors absorb excess electricity, preventing it from reaching the attached devices. As a surge protector works, it bears the brunt of the damage from the surge -- protectors are designed to intentionally fail over time, so that your more expensive devices do not.
Surge Protector Lifespan
Every surge protector can absorb a different amount of energy, rated in joules. With no easy way to identify how many joules are contained in a particular surge, however, you can't calculate how much endurance your surge protector has left. Using a protector with built-in status lights provides a way to ascertain when it needs replacement. If the "Protected" light goes out, the strip requires replacement, even if it still provides power. Some models also include an alarm that sounds at the end of the protector's life. Regardless of how many surges your protector has absorbed, you might want to replace it after the manufacturer's warranty expires, as some warranties cover electrical damage sustained by attached devices.