Stage 2 load-shedding might be required at short notice from 16:00 to midnight on Wednesday.
Breakdowns at the Majuba, Tutuka and Kriel power stations have put a severe strain on the power generation system, Eskom said.
Stage 2 load-shedding may be required at short notice should any further significant breakdowns occur.
The delay in returning two generation units at Arnot, a unit each at Kusile and Hendrina power stations has exacerbated the electricity generation constraints.
Some 4 479MW in capacity is out on planned maintenance, while another 12 951MW of capacity is unavailable due to breakdowns.
The last round of load-shedding ended on Sunday.