After the first successful tests with tree-phase electrification, the FS laid the foundation of the northern Italian three-phase network with the electrification of the Giovi line between Turin and Genoa. The E.550 was the first mass-produced locomotive for this network and was designed by Kálmán Kandó. While the electric part was constructed by the Società Italiana Westinghouse, the mechanical part was built by Ateliers Métallurgiques at Tubize in Belgium.

The locomotives had five axles of which all were driven. The middle one did not have wheel flanges and the outer ones had a lateral play of 20 mm. Only two continuous speeds of 25 and 50 km/h were realized by setting the traction motors in serial or parallel. Liquid resistors were used for all speeds between these two steps and had to be refilled with soda solution from time to time.

In comparison with the steam locomotives previously used, the capacity of the line could be considerably increased. With two locomotives per train, trains of 380 tonnes could be hauled up the 3.5 percent incline at a speed of 50 km/h. With one locomotive at the front and two pushing, the trains could even weigh 530 tonnes. In the result, their power earned these locomotive the nickname “Mulo dei Giovi” (“The mule of Giovi”).

Between 1908 and 1921, a total of 186 was built. With the introduction of the E.551 in 1921, the E.550 were transferred to less difficult lines. Many were withdrawn before World War II, but still a greater number remained in service, with the last one being withdrawn in 1965. Today, two are surviving in museums. E.550.025 can be found at St. Louis, Missouri and E.550.030 at Milan.