You should have no problem running a 4-20 mA signal 300 meters- the voltage drop will be very small and you can ignore it. The problem may by in the other PLC you are connecting to. If the 4-20 input on that PLC is isolated, it will work. Unitronics connects the negative of the analog inputs to the power supply negative (non-isolated), so if your other PLC is non-isolated the signal will end there. You will probably need a loop isolator between the two. Joe T.