Eskom warned on Tuesday afternoon of a "very constrained" power system and said it might have to implement load shedding at short notice.
"Should there be any significant breakdowns, load shedding may be required at short notice, most likely during the evening peak of 17:00 and 22:00," the utility said in a statement.
"Eskom will continue to closely monitor the system, adjust and communicate any changes as may be necessary. We appeal to all South Africans to help limit the impact of the shortages by continuing to reduce the usage of electricity and to switch off all non-essential items."
Eskom said it had 2 195MW on planned maintenance, while another 15 950MW of capacity was unavailable due to breakdowns.
"Eskom cautions the public that as the shortage of generation capacity persists, the system will continue to be constrained with an elevated risk of load shedding over the coming weeks," it added.