Rockwell Automation 1756-DH485 ControlLogix Data Highway 485 Module Installation Instructions - Manual (Page 5)

ControlLogix DH-485 Communications Module 5
Publication 1756-IN587A-EN-P - September 2005
Single-point Serial Communication Connections
Be sure that power is removed or the area is nonhazardous before proceeding.
WARNING
If you connect or disconnect the serial cable with power applied
to this module or the serial device on the other end of the cable,
an electrical arc can occur. This could cause an explosion in
hazardous location installations.