How do door safety/Interconnect safety switches work?

[borges1]

Those last couple of explanations were really helpful, thank you. You all got me the basics i was having trouble finding elsewhere. The electrical wizardry behind making machines work i find fascinating, and i am trying to learn more about it - and how to design and build my own basic systems. I've done plenty of domestic electrical work and i am comfortable doing that type of work to, or above code. but it is a lot less theory and applied knowledge, and more knowing the correct mechanics. Using low voltage switching to control higher power loads makes total sense to me now (after a few years of poking around in these things), but it wasn't initially obvioius to me. Understanding how electricity is actually making many different things happen, why different voltages, loads, controls etc are used is not something i am familiar with, but want to learn. This little revamp of my mill control box seems like a good scale to start at. I'll be sure to post some pics when i'm done.