That looks like it might have been an off switch for a very high voltage circuit. They tend to require a lot of effort to open or close, and I once saw the breaker for a 6 story office building break in a workers hand as he tried to engage it. Years of never being used can make such circuit breakers very iffy when the time comes to try to use them.

Why would we need power off comrade? We sold that device

Pretty sure it turned itself off.