One last thing and I'll get off the subject. I have made a rough sketch of a wiring diagram for the system I described toyou. Look at it and see if there is anything you don't understand about it. I am assuming the your PC simply closes a contact through which you can run your control voltage (I have used 115 volt since that is the most prevalent here). The coils AC, BC and DC are going to activate whatever you are controlling. These are coils that may close (or open) to do the job you require. They may also be small electric motors, lights, motor starter coils, etc. The coils RA, RB and RC are the auxilliary coils tha will activate the NC contacts that will interrupt the voltage going to your main coils (or other load). As you can see, this is a rather simple wiring schematic, but I believe it will accomplish your objective. Good luck!! TheCommoner