The 30 heavy (138 metric ton) 4650 kW sixaxle locomotives of the 251 series were built between 1982 and 1984 by CAF and MACOSA in Spain after a design of Mitsubishi in Japan, excluding # 001 and 002, which were delivered from Japan. The design comes from the japanese EF 66 locomotive, but not for the cape gauge of 1067 mm, but for the iberian broad gauge of 1668 mm! This type is the typical Pajares pass locomotive, pulling freights of 1000 tons with 50 km/h over the 2.0 grade from the asturian coast up to the spanish highland. This locomotive arrived from the ArcelorMittal Asturias work in Avilés with a steel coils train and waited to run back light to the spanish north coast. In Busdongo often two 1000 ton trains were coupled to form one 2000 ton train southwards.
