The Bussmann series FRS-R-400 is an energy effcient, dual-element, time-delay Class RK5 fuse and is part of our FUSETRON line of fuses. Its dual-element design provides the best time-delay for better protection of equipment such as power panelboards, combination starters, motor control centers, machinery disconnects, and safety switches. Dual element fuses feature separate overload and short-circuit elements to provide the same short circuit protection as a fast acting fuse with the added benefit of letting inrush currents pass without opening the fuse. As a time-delay fuse, it allows for temporary overload conditions without opening (sometimes called blowing a fuse). This is necessary for equipment that regularly experiences short-term power surges, such as when a motor or transformer strarts up. The time-delay feature allows an inrush current from the motor or transformer to start without opening but still protects against sustained overloads and short circuits. This also allows you to reduce the need to replace expired due to normal inrush overloads. For superior electrical protection, we recommend upgrading to Bussmann series Low-Peak LPS-RK fuses.