Issue
Equipment damage can occur when a common transformer is used to power non-isolated, half-wave rectifier and non-isolated, full-wave rectifier devices.
Equipment damage also can occur if the I/O terminals of a device lack isolation from one another and I/O devices of varying rectifier types are connected to these non-isolated terminals and powered by a common transformer.
Environment
NetController ( CX99xx , CX9702 , CX92xx , CX9xxx )
InfinetController ( Infinet Controller )
BACnet Controller ( bCXxxxx , b4xxx , b3xxx )
Cause
For example in wiring, the control signal “-” output of the full-wave device is directly connected to one of the AC leads of the common transformer through the control signal “-” of the half-wave device.
This connection places the D4 diode of the full-wave rectifier directly across the transformer secondary and causes shorting of the transformer every half cycle of the AC input.
This condition can cause serious equipment damage.
Resolution
Non-isolated, connected devices of varying rectifier types require their own external isolation transformers.
Use external isolation transformers for each device if there is doubt regarding whether an installation may cause equipment damage.
