Koeberg nuclear power station's Unit Two was not contributing to the national grid as it was shut for planned and maintenance, Eskom said in its bi-weekly status bulletin.

Supply from Mozambique's Cabora-Bassa system had also taken a dip because of a transmission fault.

Eskom said these problems put added strain on the power system, whose performance the company described as "volatile over the past couple of weeks".

"Eskom's power stations are ageing and have been run hard in the past few years in order to meet demand."

In the last year, Eskom made maintenance a priority, as it was necessary to reduce unplanned outages.

"Significant progress has been made and Eskom is on track to eliminate the maintenance backlog by the end of 2013."

Eskom urged the public to reduce electricity consumption.

On Thursday evening, the peak demand for electricity was estimated at 32,319MW, with capacity of 34,788 MW.

On Wednesday, peak demand of 32,566 MW was met by the available capacity of 35,050 MW.