Conveyor Belt Drift and Nuisance Trips

I'm a controls engineer, not a belt salesman, so I'll tell you what I actually see: most "bad switch" calls are not bad switches. The switch is doing its job. Something upstream moved the belt, loaded it off-center, or let a return idler seize, and the protection device is the messenger. This guide is written for the person standing at the drive with the line down at 2am, deciding whether to reset and run or to lock it out and fix it. When in doubt, the answer is lock it out.

I'm keeping this general enough to cover a crushed-stone plant's overland and stacker belts and a material recovery facility's (MRF) sort-line and infeed belts, because the failure modes rhyme even when the material doesn't.

Before you touch anything: the hazards that kill people on conveyors Read this even if you skim the rest. Lockout/tagout (LOTO) before any hands-on work. A conveyor is a machine designed to drag things along. If your hand is near a pinch point (belt-to-pulley, belt-to-idler, return-to-frame) when it starts, you lose the hand or the arm. Verify zero energy: breaker open, locked, tagged, and tested by trying to start from the local station after lockout. No exceptions for "I'm just going to clean this one idler." Stored gravity energy on inclines. This is the one that surprises people. On an inclined belt loaded with material, the belt and load want to run backward when you release the brake or drop the tension. A holdback (backstop) that you're about to service, or a takeup you're about to relax, can let hundreds or thousands of pounds slide. Chock, block, or crib the load and the takeup counterweight before you get under or behind them. Treat the gravity takeup weight as a suspended load — never work under it unblocked. Guarding stays on until LOTO is verified, and goes back on before restart. Nip guards, return-idler guards, and drive guards exist because people reach in. If you removed a guard to