Complex sentence: AC motors in an industrial setting tended to operate continuously and therefore large banks of resistors can be used on start-up to raise resistance and maintain torque, but this would be inefficient in a small motor designed for stop/start operation.
Split into simpler sentences: AC motors in an industrial setting tend to be operated more or less continuously and therefore large banks of resistors can be used on start-up to raise resistance and maintain torque. This would not be efficient in a small motor designed for stop/start operation.