The introduction of the first Class 5E in 1955 was the first in a long line of 3kV DC locomotives of similar external design which continued right up to the delivery of the last Class 6E1 in 1985.

This family of 1849 locomotives haul almost all services on the DC electrified routes of SAR. The original 5E class were built in England and totalled 220. They are now being steadily withdrawn and the remaining examples are used on the Cape Western system. A slightly more powerful version with detail differences such as regenerative braking was introduced in 1959 and classified Class 5E1. Altogether, some 690 5E1's were built between 1959 and 1969. The first batch was built in England, but subsequent deliveries starting with E591 in 1963 were built in South Africa by Union Carriage. The 5E1's were used on virtually all of the DC electrified lines in South Africa, although withdrawals of the early British built examples started in earnest during 1989.

The 6E/6E1 classes are externally very similar to the earlier classes but mechanically they are very different. They are considerably more powerful than the 5E1's and this is achieved by optimising power transfer to the rails.

On the 6E's this takes the form of air bellows between the frame and wheels and on the 6E1's by sophisticated traction links on the outside of the bogies, this feature making the 6E1's immediately recognisable.

The Class 6E1 totals 960 and is the largest class to operate on the SAR. One 6E1 (E1600) was converted to a testbed for AC locomotives and now operates on the AC lines whilst another, (E1525) was modified for high speed experiments and holds the world narrow gauge speed record of 245 km/h (153 mph).

A large number of 6E and 6E1 locomotives are currently being formed into permanently coupled pairs and have been reclassified 16E and numbered in a new series between 16001 and 16711.