M172 BACnet MS/TP Wiring

[cloud_74]

Hi everyone,

Is the BACnet wiring to a M172 a 3 wire or 2 wire system?

My understanding is that needs to be a 3 wire system. If a wire BACnet system is used (no GS connected) would this cause communication issues?

[FedericoM · Accepted solution]

Hello,

the RS485 of M172 is isolated, GS should be connected, I would say that in general the RS485 ground should be always connected among devices...but often works even if it is not, it depends by each system architecture.

[Bastian_Schmitz]

As additional information. The RS485 is isoleted on the TM172O, on the TM172P with 7 and 18 IOs. And on all TM172P28 42 which has an I on the end of the Reference. 

There are some old References which are not isolated. But only the 28/42 IO Version.