Cape Town - Eskom issued an alert on Thursday that the power system in under severe pressure as a result of technical faults.
"Units that were on maintenance have experienced outage slips which means the units could not be returned back online on their due date from the outage."
The power utility said it asked key industrial customers to cut their load by a minimum of 10% as from 17:30.
It also called on household consumers to switch off geysers, air conditioners, pool pumps and non-essential appliances from 17:30 to 22:00 to prevent the need for rotational load shedding.
"Should we not achieve the required energy savings, we may need to go into load shedding from 18:00 until 22:00 tonight," it warned.
On Wednesday, Eskom also asked consumers to save electricity because of technical problems and the loss of additional generating units.
Sapa reported earlier this month that work at Eskom's two controversial power stations, Kusile and Medupi, have been progressing well.
Unit one of the Kusile power plant switched on the barring gear motor, which is a mechanism to ensure a turbine does not bend.
Unit six of the Medupi power station also fired up its first gas burner and received a pressure equipment regulation certificate from the labour department.
- Fin24 with Sapa