Everything goes along fine day after day, year after year. Pretty soon grandpa's barn is your barn, and it's not just 30 or 40 years old, it's 60 or 80 years old. Old barns are neat – there's just one catch. When was the wiring last inspected? When was it last updated?
The wire in this photo is form a real barn that didn't burn down, only by the grace of God. The culprit in this case was mice, chewing on wires in walls filled with insulation. It was a barn used for farrowing. The only reason this stretch of wiring, which didn't turn out to be the worst stretch in the run, didn't burn the barn down this winter is because it ran to a light outside the barn that isn't used in the winter. In other words, it wasn't turned on all winter long.
It was discovered when wires to the overhead lights in the barn shorted out. They also were damaged by mice chewing on the wires. The electrician called in to diagnose the problem and suggest solutions said the bare wires touched a piece of metal conduit, causing the short. The only reason the barn didn't burn down at that point is because it shorted out while the farmer was in the barn doing chores. He sometimes leaves the lights on. On any given night the sparks could have ignited the insulation, and sent the barn and animals inside it up in flames.
Meeting code is a tricky business in livestock barns, this electrician notes. There are different interpretations about how wiring should be installed if you're replacing wiring inside the walls with wires run on the outside of the walls. Different rules suggest different standards. The key, however, is switching to a system that is safe, and not risking a major calamity by chancing that nothing will go wrong with damaged wires.