I was working on a control system for cattle feed mills. We had to wire into the system sensor-by-sensor and actuator-by-actuator as they continued to make feed

I was working on a control system for cattle feed mills. We had to wire into the system sensor-by-sensor and actuator-by-actuator as they continued to make feed. We started out with the entire system simulated, then gradually ended up with a fully live system. I (thought I) set an actuator running an auger (screw) that offloaded the feed from the mixer into a leg (12 meter tall vertical screw) to "run always." That should be safe right? The auger runs all the time, carrying away anything that dumps into it. What I had actually done was set a hay belt to "run always" it was stuffing the mixer with more and more hay until it was a solid mass inside the box. Everything seemed fine when we started that next batch of feed... then the mixer started. The lights dimmed and there was this shriek of metal and a bang from the mill floor. We shut down and went out to see this huge mixer hanging off a drive chain at 45 degree angle from the floor. Bolt heads the size of manhole covers had sheared off and were lying nearby. Fortunately no one had been standing nearby. I don't know if my memory matches reality, but I recall a light from one of skylights shining down on it in the grain dust like a spotlight. I was pretty sure this was going to be my last day on the job. I walked over to stand next to the Mill Manager, a salty fellow named Marvin with three fingers on his right hand. Marvin looked up the chain and back down to the bolts on the floor and said "Yep, it'll do that." Two workers lowered it down and welded the bolt heads back in place like they did it every day. I was with the company for five years. I don't recall every having a support call from that mill after we finished the installation.