A Liebert SiteLink panel is not communicating with the Niagara R2 UNC using BACnet/MSTP.

Issue

A Liebert SiteLink panel is not communicating with the Niagara R2 UNC using BACnet/MSTP.

Product Line

TAC I/A Series

Environment

  • Liebert SiteLink panel
  • Niagara R2 UNC
  • BACnet/MSTP communication

Cause

Termination resistors

Resolution

When connecting a dedicated Liebert SiteLink module MSTP segment to the UNC, the EIA-485 trunk typically requires 120-ohm termination resistors at each end. Field testing has determined for Liebert Sitelink-4 and –12 modules that the termination resistors have a negative affect on communication even at a low baud rate of 9600. Removing the termination resistors resolved the communication issues.