DESC: Transient voltage surge suppressor (TVSS). Hybrid technology thermal-fuse metal oxide varistor and gas discharge tube (GDT) design. Ride-through sustained overvoltage up to 240 volt AC, suitable for connection to power systems whose available short-circuit capacity does not exceed 25,000 amp symmetrical short-circuit current when protected by the recommended branch circuit protective devices. Flush (Type 1 housing only) or surface mounting installation. Provides AC line protection for the whole house andprotects four telephone lines and up to two coaxial lines with Gas Discharge Tube (GDT) technology. All modes protected (L - L, L - N, L - G, N - G). It is designed for use on single-phase, three-wire, 120/240 volt AC, 50/60 Hz electrical service. The LEDs on the face of the AC module indicate the operational status of the AC protection. If the LEDs for each line are on, the device is fully operational. If either of the LEDs go off, the AC module should be replaced.