How do I know when a surge protector has gone bad or burned up inside?

There are several hundred TVSS devices available for purchase. How can you tell if the once you have selected is a quality device? Make sure the device United Laboatories (UL) listed as TVSS or Transient Voltage Surge suppressor. Also, make sure that it meets UL standard 1449, the number of the UL test for TVSS devices. Both of these pieces of information will be shown on the UL label. Some equipment sold as surge protectors are not listed as TVSS, but are instead listed as a "current tap". These devices will have the word TAP rear the UL label and should be avoided for use as a TVSS. In addition, the UL label should be list a clamping Voltage of 500 volts (.5 kV) or less for plug-in TVSS, or commensurate with your service voltage on hardwired TVSS.