The series 11 is a series of twelve electric bicurrent locomotives ordered in 1985 by SNCB to be able to tow the Benelux trains to the Netherlands, where the network operates under 1.5 kV. They are painted in Benelux livery (burgundy and yellow).
The 12 series is a series of twelve electric locomotives bicourant ordered in 1985 by the SNCB to be able to make connections with France.
The Series 21 locomotives are electric locomotives of the Belgian Railways (SNCB) equipped with thyristor choppers to modulate the starting power. They are technically very close to those of the 27 series, but with a lower power.
The SNCB Series 27 locomotives are equipped with thyristor choppers that modulate starting power. Locomotives in series 11, 12 and 21 are directly derived from these engines, but with less power or the ability to travel in several countries.