JOHANNESBURG - "Extremely cold weather has... resulted in an increase in demand nationally, particularly during the evening peak hours between 5pm and 7pm," it said in a system status bulletin.

"Peak demand this evening is expected to reach 36,258 MW [megawatts], the highest so far this winter, and customers are urged to switch off all non-essential electrical appliances during the peak hours."

Eskom said supply had been restored to parts of the Eastern Cape after outages because of the inclement weather at the weekend.

"Eskom continues to monitor weather conditions around the country closely, after snow and heavy rain affected power lines and sub-stations in the Cape and elsewhere over the weekend," it said.

"Eskom had anticipated inclement weather and had staff, helicopters and equipment on standby."

A unit at the Koeberg nuclear power station, in Cape Town, had returned to service after automatically shutting down on Wednesday because of an electrical fault.

Total demand on Monday evening was forecast to reach 36,258MW and Eskom had 36,580MW of capacity available, including from open cycle gas turbines.

Current planned maintenance accounted for 2250MW. Unplanned outages affected 4100MW.

On Sunday, peak demand of 34,094MW was met, with an available capacity of 35,752MW.

On Saturday, peak demand of 33,387MW was met, with an available capacity of 36,338MW.

Peak demand for the rest of the week was forecast to reach 35,825MW on Tuesday, 35,535MW on Wednesday, 35,464MW on Thursday, 33,675MW on Friday, 32,464MW on Saturday and 32,755MW on Sunday.