So we had a debate in the shop of proper wiring of guards today. New school says soon as you add and new e-stop or guard switch the safety circuit needs to come up to today’s standard (dual redundancy, safety relays ect ect). Old school says only time it needs to meet new standards is if it’s a new machine. The circuit which switch is being wired to has the e-stops and guard switches wired in series to a relay. I can see both points but I am having a hard time finding information what is the proper way. Any help would be greatly appreciated.