The power utility said high demand and a shortage of capacity were to blame.
Eskom also said it might not be able to suspend the power cuts during Thursday’s peak hour traffic periods.
Spokesperson Sikonathi Mantshanthsa said that the grid was not improving as expected.
“South Africans need to remember that we’ve been using the reserves the whole week. What we have seen is much higher demand than we expected. We’ve seen a demand for and extra 2,000 megawatts over the past two days.”
In a statement, the utility’s boss Andre de Ruyter said that they did not take the decision to load shed lightly but it was unavoidable he stressed.