HIGH-SPEED CLASS J FUSE T-PACK 30A. LDFJ series fuses provide space saving, high-speed performance and short-circuit protection for AC and DC drives. LDFJ series offers current limiting features with lowest I2T for protection of power semiconductor devices and motor controllers. Applications: All AC/DC drives (Including variable frequency drives), power converters and solid-state devices, resistive loads, such as resistance electric heat.