The second generation of electric locomotives known as “BB Midi” consisted of the E 4100 and the E 4600. The E 4100 was intended for mixed service and had a shorter gear ratio than the E 4600. It was therefore used for freight and passenger trains on the lines in the Pyrenees. They were designated BB 4100 by the SNCF and were partially rebuilt into the BB 4600 in the 1950s. This meant that they could now reach 90 km/h and could also be used on flatter lines. When more locomotives were needed for freight service again, they and some original BB 4600s were converted back into the BB 4100. From the end of the seventies they were used in shunting services, where the last ones were retired in 1987. 