Eskom warned on Thursday that while no load shedding was immediately anticipated, there was a "high probability" should any further capacity be lost.
The system was severely constrained, Eskom said in a statement shortly before 18:00.
This was caused by the loss of multiple generation units and high load losses, as well as generation units that were already in planned maintenance - the latter alone amounting to over 7 500 MW. Over 10 800 MW of capacity was out on unplanned maintenance, Eskom said.
Teams were "working around the clock", it added.