I once got called out on a problem with a 500HP soft starter on an "Edger", a horizontal circular gang saw with 54 blades on a shaft cutting slabs of wood into fence boards. Whenever they first started the machine in the morning, there was an awful banging sound coming from the soft starter, but the rest of the day it was fine. Everyone there, including the plant electricians, were affraid of the soft starter because they didn't understand it, but they did know that it didn't have any moving parts so there shouldn't be anything banging.
What it turned out to be was that in the morning, the saw blades would shrink in circumfrence, but actually widen by just a tiny fraction of an inch. They had blade guides on them, Delrin blocks with slots in them that actually touched the blades to keep them from warping. In the morning when the blades were fatter, the small amount of additional friction, multiplied by 54 blades, translated into so much extra load that the soft starter would stay in current limit until the ramp time would expire, then go across-the-line. When it did, because the blades weren't moving yet, the current jumped to 3500A, and the cables inside the soft starter cabinet broke out of their straps and started banging on the enclosure walls.
