Comment by chiph

A bank I did some contracting for had a problem where their Token-Ring network would crash at random intervals during the day in one of their branches. It would also crash at night, but the times when it would happen were more predicable.

And that was the clue they needed to solve the problem - it turned out that the wiring installers had run the cable up the elevator shaft. When the elevator stopped at a certain floor the door motor was sometimes interfering with the signal. The more-regular nightly disruptions were because of the security guard making his rounds.

It turned out that run was pretty close to the length limit for 16mbps Token-Ring, so they added a repeater in the middle to boost the signal strength.