North American UL/CSA and IEC standards for overcurrent protective devices require significantly different Time-versus-Current characteristics. UL rated fuses are tested to open at 135% of rated current while IEC fuse ratings are tested to carry 150% of rated current. Be aware of these differences as the fuses are tested and specified differently between these standards for products sold in different parts of the world. The physical dimensions and materials for both UL and IEC fuses are similar. However, fuses made to the different standards are not interchangeable. The element melting and opening times will differ when subjected to the same magnitude of current. The circuit designer must consider that different world markets may be subject to different fuse agency standards.