Unlike the previous electric locomotives used on mountain lines, the new locomotives had to be able to vary their speed, a capability which at the time was difficult to achieve, due to the fact that the three-phase motor spins at constant speed set by the feeding current frequency.

[1] The wheel arrangement chosen was 1′C1′, similar to that adopted on the contemporary 685 class of steam locomotives.

The production contract was signed in 1913, construction of the new units beginning at Società Italiana Westinghouse, which had designed the locomotive under the direction of Kálmán Kandó.

The mechanical parts were co-built with Società Italiana Ernesto Breda.

They were later used also in Lombardy on the local three-phase lines, until, from 1962, the railroads were adapted to the now standard 3,000 V direct current electrification.