The CCL repeated the surge test at 600 volts peak amplitude with a new USR V.Everything modem. Again the USR modem failed. ZoomGuard TM technology raises the cost of goods of Zoom's modems, but drastically reduces the probability of field failure from lightning compared to U.S. Robotics and others. All current V.34 Zoom modems and ISDN products are protected by ZoomGuard. Copies of Communication Certification Laboratory's test report and letter summarizing the test report are available from Zoom Telephonics at no charge on request.
Lightning is the most common cause of modem failure.
Direct hits to overhead lines occur, but far more common is the induced surge on a buried cable. In the United States, the high point of thunderstorm activity is in western Florida, with a ripple effect out from this focus of lightning activity. The high lightning level of the southeast extends all the way west into eastern Texas. In addition, the United States has intense thunderstorm activity in areas of Colorado, New Mexico and Arizona. April is the beginning of lightning's primary season that extends over six months, ending in early October.