Soft starters and VFDs are each used to reduce the in-rush current on the electrical utility during start-up of the pump station and/or electrical generator. They are necessary when the utility has restrictions on the horsepower of the machine being started or if there is a soft utility line that cannot handle the in-rush. Soft starters accomplish this function with basic controls and are much less expensive than VFDs. While more complex and more expensive, VFDs can match the speed of the pump(s) to optimize performance and offer more diagnostic capabilities. Constant level applications primarily use VFDs.