SurgeArrest components such as MOVs and Thermal fuse ensure instantaneous reaction to lightning strikes and wiring faults. If the surge components are damaged due to power spike or over voltage, excess power cannot reach your equipment. Unlike the APC SurgeArrest products, most surge suppressors continue to let power through even after circuits have been damaged, leaving your equipment exposed to other damaging surges. APC surge protectors undergo stringent testing by IEEE, and are awarded “let-through ratings”, which indicate the maximum voltage level that can possibly reach your equipment after a surge or voltage spike has passed through an electric surge protector. Lower IEEE let-through ratings indicate better protection and performance. The APC Essential SurgeArrest series offers optimal performance with a let-through rating of less than 330V for North American products, and a rating of less than 15% for products sold worldwide. All APC products comply with local agency safety requirements, including UL in North America and CE/Kema/Gost/C-tick/A-Tick/Telepermit in their respective regions. SurgeArrest will warn you if its circuitry has been damaged by heavy strike or power line surge and it is unable to provide 100% protection. If still under warranty, APC will then replace your damaged SurgeArrest free of charge.