4-20mA PLC analog output ground referencing for other devices
Hard to tell without datasheets for the relevant products, but it sounds like the driver lacks isolation between the 4-20mA input and the mains. If so, this is a rather sub-standard design. 

You can use it if you add a 4~20mA:4~20mA isolator between the PLC and the driver. Make sure the isolator is rated to continuously withstand mains voltage.