Hello all! I am new here but think this will be a great resource and hopefully I can also be a help to some people. Recently, I had a project at work that has me confused. The machine is being run on an A series PLC. We needed to have ethernet capability for some processes so due to cost, added an FX5 PLC. It is a transistor model and is configured for NPN. This is where it gets weird. I have inputs for the finger swipe inputs and light curtains tied off of the A series inputs at a terminal strip and going to the FX5 (Just added the FX5 wire to the existing wire on the terminal strip) the breaker for the FX5 is only on the positive 24VDC wire. When I trip this breaker, the FX5 inputs all go "true" or, provide a neutral to the inputs which sets the A series inputs true at that point, disregarding the light curtains being blocked and energizing the "start" inputs as well...basically creating a death trap. I am only assuming that somehow the neutral from the output side COM terminals is somehow being connected to the FX5 inputs when the power is killed? I put a double pole breaker in to break BOTH positive and neutral in the event it tripped and this solved the issue but, trying to understand how this was possible. Any help would be greatly appreciated! Thank you!