After all, it does no good to protect the power to sensitive equipment, only to have the surge enter through the phone or cable lines. A surge protection device that protects both electric circuits and telephone lines will be listed with both UL 1449 and UL 497a, respectively. The listings will be verified on the back of the device by a UL sticker. You should also choose a device with an indicator light or other diagnostic feature to confirm the device is working. The package should have a UL 1449 listing, generally between 330 and 600 volts.
More desirable models have a third mode called neutral to ground.
Terms vary and should be considered carefully to determine if such coverage is of value to you. Using a surge protection device Ensure that all electrical entrances to the equipment are protected by an SPD with the surge reference equalizer capability. Plug the SPD into an outlet that is properly wired and grounded, and make sure that your meter and circuit breaker box are properly grounded. Check the indicator light or other diagnostic feature on the SPD regularly to ensure it is working. Never plug an SPD into an extension cord.