Eskom said on Thursday that power cuts of up to 4,000 megawatts (MW) would last until Friday, as it was waiting for regulatory approval to reconnect a unit at nuclear power station Koeberg.
Earlier it had said cuts could last until further notice.
Eskom, which produces more than 90% of the electricity in Africa's most industrialised economy, ramped up power cuts to 4,000 MW on Tuesday after a fault with a pump at Koeberg, the country's only nuclear station.
That compounded breakdowns at the company's coal fleet, which accounts for the bulk of its 44,000 MW nominal capacity.
Eskom has repeatedly implemented nationwide power cuts in the past year that have dented economic growth and hurt business sentiment.
Manufacturing data later on Thursday is expected to reflect the impact of the power outages.
Eskom hopes to bring Koeberg Unit 1 back to service by Sunday, which should reduce the scale of the outages.
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