Eskom has been battling to keep the lights on despite low electricity demand over the Christmas and New Year public holidays, with the company contending with breakdowns at its creaking fleet of coal-fired power stations.
The cash-strapped utility said cutting up to 2,000 megawatts (MW) of power from the national grid overnight would help it to replenish emergency reserves to meet electricity demand during daylight hours on Wednesday.
Eskom said in a statement that 13,600 MW of its 44,000 MW total nominal capacity was offline on Tuesday because of plant breakdowns. It last implemented power cuts on Sunday.
Eskom generates more than 90% of the electricity in Africa's most industrialised economy, but its unreliable performance is a major impediment to President Cyril Ramaphosa's efforts to revive economic growth.
Eskom's new chief executive Andre de Ruyter started work on Monday and will oversee a government plan to split the company into separate units for generation, transmission and distribution to improve its performance.
(Reporting by Alexander Winning; editing by David Evans)