A whole-house surge protector should be replaced after it absorbs a significant surge event, when its status indicator light shows it is no longer providing protection, or after approximately 10 years of service — whichever comes first. Many homeowners don’t realize that surge protection devices have a finite lifespan: the metal oxide varistors (MOVs) inside them degrade a little with each surge they absorb, and eventually they’re depleted. A depleted SPD may still have power running through it but is no longer protecting anything.

How Surge Protectors Wear Out

The protection element in most surge protective devices is a metal oxide varistor — a component that absorbs excess voltage by converting it to heat. Each time the MOV absorbs a surge, whether a massive lightning strike or the smaller, more frequent surges that come from motors cycling on and off inside the home, a little of the MOV’s capacity is used up. A large surge (like a nearby lightning strike) can wipe out most or all of the remaining capacity in a single event. Smaller surges degrade capacity gradually over time.

The Front Range sees some of Colorado’s most active thunderstorm activity, particularly during afternoon summer storms. Denver averages around 35–40 thunderstorm days per year, and lightning-related surges are a real risk — especially in open suburban areas and near ridgelines where homes can be exposed.

Signs Your Surge Protector Needs Replacement

  • Status indicator off or red: Quality whole-house SPDs include an LED or indicator light that turns off or changes color when protection is depleted. If the light is out on a device that’s still powered, the MOVs have likely failed.
  • Recent lightning strike nearby: Even if the indicator still shows green, a known nearby strike is reason to have an electrician inspect and likely replace the unit.
  • Age over 10 years: Even without a dramatic event, the cumulative effect of normal surges depletes MOVs over time. Plan replacement as part of routine electrical maintenance after a decade.
  • Appliances or electronics have failed: If you’ve had unexplained electronics failures despite having an SPD installed, the protector may have been depleted before the device failed to do its job.
  • No audible alarm silence: Some units include audible alarms when protection fails. If yours beeped after a storm and then went silent, that may indicate the unit has failed open or depleted.

What Happens If You Don’t Replace It

A depleted whole-house surge protector provides zero protection. The next surge — from a lightning strike, a utility switching event, or even a large motor starting in the home — passes through to your electronics, appliances, HVAC system, smart home devices, and anything else connected to the home’s circuits. Modern homes have far more electronics embedded in appliances than homes of 20 years ago: variable-speed HVAC motors, smart thermostats, EV chargers, and connected appliances all contain circuit boards that can be destroyed by a surge event.

Replacement and Upgrade Considerations

When replacing a whole-house SPD, this is a good opportunity to upgrade to a higher-capacity unit. SPDs are rated in joules (energy absorption capacity) and kA (kiloampere surge current rating) — higher numbers mean more protection. A unit with a higher clamping voltage responds more quickly and limits the voltage that passes through to your circuits. Some newer units also include diagnostics that report protection status through an app, eliminating the need to physically check the panel indicator. Done installs units that are UL 1449 listed and properly matched to the service entrance size.

For whole-house surge protection installation or replacement, see Done’s smart home and safety services. If you’re concerned about your panel’s overall condition or want to assess your home’s complete surge protection strategy, our panel and wiring team can walk through your options. For generator and battery backup solutions that keep your home running during outages, visit our backup power page.