There was no difference in power between the classes as they all used the same traction motors and control equipment.

Six of the 23s (2306-2313-2317-2320-2321-2331) later received an extra vent on one side only, just above the existing central one.

The reason for these differences was to let them pull heavy freight trains on the line Brussels-Luxembourg.

It also was given the ACEC Type G transmission system with a different gear ratio to test.

As time went on the four voltage requirement was dropped and the actual production locomotive became the Class 20, introduced late in 1975.

124.001/2401 made a number of test runs between Landegem and Aalter at speeds up to 200 km/h (124 mph).