The Model 8021NX is a DIN Rail mounted surge suppressor for 2-wire
RS-485 circuits used to protect factory data networks, or, any RS-485
network that wants to avail itself of the DIN Rail packaging concept.
The Model 8021NX provides common-mode (line to ground) surge protection
and differential mode (line to line) protection for balanced networks.
All the inputs, outputs and ground connections are via screw terminals
located on the top surface of the device.