In the Great Lakes Region it was common practice to build a factory and power plant on the same property. This way power was more easily distributed and controlled. Over time centralized power plants distributing power through copper wires became the norm.
One factory experienced many health complaints from their workers, including headaches. An outside consulting firm found no problem with the factory air or emissions. Those troubled with the headaches were pinpointed to working in the reactor area. One epileptic worker even experienced a seizure in the elevator so severe he decided never to step foot in the building again.
After looking at the old wooden elevator the consultants noticed the florescent bulbs were flickering. What was making these bulbs flicker and what was causing the workers to experience these health complaints?
Here's the rest of the story.
A little detective work revealed that the elevator and some of the other areas of the building were running on 25 cycle power, and the power source was the original power plant generator.
In the early days of power development there were no standards and many different voltages and frequencies were used. Even today, different countries run different frequencies.
The old motor still worked but they needed 25 cycle current, not the standard 60 cycle variety. While it is easy to change voltage with a transformer, changing the frequency is costly. So rather than replace all the old motors, including the elevator drive the company simply continued generating its own power.
At 25 cycles even filament bulbs flicker, and flicker will cause headaches in some people. The solution was to wire all lighting with standard 60 cycle power and let the ancient motors chug along on 25 cycles.