I'm a graduate engineer at a manufacturing plant and unfortunately my lack of experience shows. Today I had the simple job of connecting the output of a limit switch on a circuit from a machine to the input terminal of a robot on a separate circuit. Both use 24v DC. I failed horribly. Probably because I attempted to use a single wire and evidently electricity needs to flow in a loop. As both machines were running of the mains wouldn't there already be a loop present? And at the risk of sounding even more silly, does there need to be a loop, or are the electrons just trying their best to get to ground (0v)? I was actually under the impression 24v would travel to 0 volts through a single line no matter what the conditions. Finally what would be the best way to wire these two circuits together. Maybe the 24v from limit switch should be run through a relay to isolate the circuit and having a second wire run between the machine neutral and the robot neutral? I honestly have no idea. I will try and draw up a little diagram in paint. Thanks in advance for any assistance. This is really eating at me, and I it would help me out a lot. Pretty confused at the moment.