US Robotics 002805-00 Getting Started page 60

For your own protection, make sure that the electrical ground
connections of the power utility, telephone lines, and internal
metallic water pipe system, if present, are connected together.
This precaution may be particularly important in rural areas.
WARNING: Do not attempt to make such connections yourself;
contact the appropriate electric inspection authority or
electrician.
Warranty and Notices C-5