Most SINAMICS G120X conversation happens at 380–480 V in pump rooms, but the 200–240 V variants quietly serve a different world: small booster pumps, roof fans, and packaged equipment where the building management system — not a PLC — is the master. There, the network question changes shape: the master speaks BACnet MS/TP or Modbus RTU, not PROFINET, and the drive must join that world natively.
Follow the master, not the datasheet
If the master controller is a building automation head-end, BACnet MS/TP is the language it dreams in — objects, priority arrays, schedules. If it is an OEM packaged controller or a small RTU, Modbus RTU is the lingua franca with a decade of register maps behind it. USS is Siemens' serial protocol for direct drive control — compact, fast to commission, and at home when the master is another Siemens device or a simple panel that only needs run/stop/speed plus a fault bit.
Catalog examples cover the spread: the 18.5 kW USS/Modbus G120X drive serves the serial world, while the 3 kW PROFINET unit marks where the factory-network world begins. Below these, the 1.5 kW PROFIBUS DP variant bridges legacy DP string installations.
Every one of these sits inside the VFD catalog, so the honest comparison is about the master system, not the drive family.
Can one drive serve two masters?
Not simultaneously on the same port — the G120X has one fieldbus interface per control-board variant. If both a BMS and a local PLC need control, decide who owns run command and who only monitors, then wire accordingly.
Is USS obsolete?
No — it remains the lowest-overhead option where a Siemens panel or another USS master drives a single motor. It lacks the open-ecosystem tooling of Modbus, so for anything the facilities team must service themselves, Modbus RTU with a published register map ages better.
