Hardware manual

PCI VELOCITY / OPTO ISO RS422/485 RS422/485 Information
Chapter 4 Page 49
with a strap to connect signal common and protective ground
directly together when specific installation conditions necessitate.
Configuration B) The circuit common shall be connected
directly to protective ground. The same configuration need not be
used at both ends of an interconnection; however, care should be
exercised to prevent establishment of ground loops carrying high
currents. (Note: Under certain ground conditions in configuration
A, above, high ground currents may cause the resistor to fail;
therefore, a provision should be made for inspection and
replacement of the resistor.)