This is the 6-amp model from the popular STR-4 series of speed controllers, which includes models ranging from 1.5 to 14 amps. The STR-4 allows you to control the speed of your three-phase fan. Thanks to its autotransformer technology, it delivers a well-regulated output voltage to your fan, ensuring smooth motor operation and extending its lifespan. The external dial on the unit allows you to select from 5 speeds. Turning the dial from the zero position provides an additional 230 VAC output. This can be used, for example, to connect a damper or an operating status light.