APC surge SurgeArrest Essential 7 Outlets Surge Suppressor 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 a surge protector. 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. Protection of phone lines ensures complete protection of your equipment from surges. It is very important to protect your equipment from back door surges traveling through data lines, as they can be as damaging to your equipment as surges traveling over power lines.