"So, what went wrong? Varying load conditions in the three legs of the 3-phase circuit caused tremendously strong and dynamic magnetic field changes. The electromagnetic forces between the three conductors and the steel pipe (gack!) cause the conduit to wiggle around inside the pipe."
This is sort of like the electrical engineering equivalent of the Tacoma Narrows Bridge collapse:
This is sort of like the electrical engineering equivalent of the Tacoma Narrows Bridge collapse:
https://en.wikipedia.org/wiki/Tacoma_Narrows_Bridge_(1940)#C...