March 2012 – Our BACnet® multi-network routers continue to be popular components in the Building Automation market. However, there is a simple wiring error that many installers make in setting up these units to route between BACnet MS/TP and BACnet/IP.
Our MS/TP port uses an isolated EIA-485 transceiver which is connected to a 3-pin removable connector. Two of these pins are the standard + and - terminals to which you attach EIA-485 twisted-pair. It is the third pin – the SC terminal – that confuses installers. Our SC pin ties to the transceiver ground.
SC is sometimes mistakenly thought to mean Shield Connection – and on some equipment from other vendors it might mean this. But on our unit SC stands for Signal Common. And this pin must absolutely be attached to the same signal reference that is shared by all devices on the MS/TP trunk. If this connection is not made, MS/TP communication will never be reliable.
For more information, refer to the installation guides for the BASRT-B and the BASRTP-B – respectively available at: