WPI Inverter Duty motors from Nidec Motor Corporation meet NEMA premium efficiency levels. The 15 to 30 hp vertical high-thrust motors protect against harmful effects when the motors are used with a variable-frequency drive, including a shaft grounding ring to discharge shaft current without harming the bearing, and winding thermostats to protect the motor from incidental overheating when operated at low speeds for extended periods. 888/637-7333; www.usmotors.com.