Power utility Eskom on Thursday again declared an emergency to keep the country's lights on.
It requested large industrial consumers to reduce their electricity consumption by 10% until 9pm on Thursday night, Eskom spokesperson Andrew Etzinger told the Mail & Guardian.
As of Thursday morning, four generating units developed "technical problems", he said, leaving the security of supply vulnerable.
"As per regulatory protocols available to us, we declared an emergency, asking all large industrial users to reduce their load by 10% today until 9pm this evening," he said.
Eskom would reassess the situation again on Friday.
Etzinger said it was confident "certain generation units will be back in service by then".
The company's call follows a similar emergency that was declared in November last year. The loss of a transmission line from Cahora Bassa, in Mozambique contributed to the shortage in supply.
Etzinger said Eskom had teams on their way to the site and it expected the power to be restored by the weekend "at the latest".
In a statement released just after the emergency kicked in at 2pm, Eskom said it would make every effort to avoid a blackout.
"We are hopeful that by applying these measures, coupled with support from all electricity consumers, we will achieve the required load reduction necessary to protect the national grid," it said.
The utility called on all customers to reduce their electricity consumption. Commercial customers, particularly shopping centres and retail outlets were requested to immediately switch off geysers and to adjust air-conditioning temperature levels to 23⁰C.
The loss of productive capacity has been a major frustration for industry across the country.
The country's power grid has been operating on very thin margins as Eskom performs required regulatory maintenance on its power stations over the summer months, and works to build new power stations to meet demand.
The completion of the new Medupi and Kusile power plants has, however, been repeatedly delayed over a number of years. The first 600MW unit of Medupi is only expected to come on line at the end of this year.