Eskom warned in an alert on Tuesday afternoon that it would implement stage 2 load-shedding from 10pm throughout the night.
"Eskom would like to inform the public that stage 2 load-shedding will be implemented starting at 10pm until 5am tomorrow. This will be repeated on Wednesday night," the power utility said.
"This load-shedding is necessary to preserve emergency generation reserves in preparation for higher demand expected during January as economic activity resumes. During this period, Eskom will continue to pursue increased reliability maintenance as planned and previously communicated."
Eskom said it had removed 9,745MW from the grid due to planned maintenance, while another 11,346MW of capacity was unavailable due to unplanned maintenance. It said teams were "working around the clock to return as many of these units to service as soon as possible".