Eskom said on Sunday that controlled load shedding will return because of a shortage of capacity.
The utility said in a statement it would cut 2 000 megawatts from the grid from 13:00 until 22:00. It is also replenishing and preserving emergency water and diesel to limit the possibility of further outages in coming days.
Blackouts became familiar in 2008, and again in 2015, when Eskom implemented months of these outages known locally as load shedding.
The cuts hamstrung the economy, limiting industrial output and hurting business and consumer confidence.
In his annual State of the Nation Address, President Cyril Ramaphosa last week vowed to rescue Eskom after it suffered massive losses and piled on debt.
Ramaphosa said that a split into generation, distribution and transmission businesses will enable each unit to manage its costs more effectively and make it easier for them to raise funding.
Eskom is seen by rating agencies as a key risk to SA's economy, with blackouts and huge debt a drag on growth prospects.