Issue
Infinet/MSTP was running fine until a device was added or replaced, after wiring in the new device it brings down the Infinet/MSTP field bus when powered up, disconnecting the new device from the bus makes the bus resume operation.
When the new device is connected the green (RD) LED goes solid instead of blinking and all communications to all devices on the bus stops, in some cases the master controller will reset.
Product Line
Andover Continuum, EcoStruxure Building Operation
Environment
- Infinet devices
- i2s
- MSTP devices
- b3s
Cause
Power lines reversed. Continuum field devices (i1s, i2s and b3s) have their RS-485 communication lines connected to ground via an isolator as seen in the diagram below, if the LIVE and GND lines are inverted then LIVE is connected to the 485 communication lines instead of GND.
This will make the field bus electrically unable to communicate and, in some scenarios, can even cause hardware damage.
Resolution
Ensure Correct Wiring:
- When powering 24VAC devices off the same transformer, make sure to continue the wiring chain LIVE to LIVE and GND to GND.
- In the field, it may not be very obvious that the 'Live' and 'GND/Neutral' wires have been swapped. A multi-meter can be used to verify the wiring.
- Set the multi-meter as appropriate to measure 24VAC.
- Place the black lead of the meter on the GND/Neutral termination at the power connector of the field device.
- Use the red lead of the meter to measure the voltage at the +/- termination at the RS-485 (Infinet or MSTP) on the controller.
- The measured voltage should be very low, between 0 VAC and 1.1 VAC, a voltage reading of about 10 VAC indicates the Live and GND/Neutral wires have been swapped.
