Eskom has started with its load shedding at 09:00 on Thursday morning and it will most likely continue until 22:00 on Thursday evening, spokesperson Andrew Etzinger told Fin24.
Etzinger said they are constantly monitoring the situation and should be able to give a better indication later on Thursday whether it will continue on Friday as well.
Since 2008 Eskom has implemented measures at power stations to increase resilience against heavy rainfall, Etzinger told Fin24.
"The current situation is, however, that after days of continuous rainfall in Mpumalanga, even those contingencies are no longer valid."
A second factor is that at certain power stations there are open cast coal mines. Therefore it isvulnerable to the weather.
Thirdly, the transportation of coal to power stations makes it vulnerable to rain.
All these factors had a culminating effect, leading to the current need for power shedding.
Etzinger said the load shedding schedule is available on the Eskom website at eskom.co.za load shedding or people can call the Eskom call centre on 08600 37566.
Another Eskom employee in the media department told Fin24 that the load shedding will be done on a 2-hour rotational basis.
Etzinger said municipalities were informed of the need to reduce electricity and they would decide in which suburbs to cut power.
Etzinger could not say if power cuts would affect the Oscar Pistorius murder trial in the High Court in Pretoria.
He said the Tshwane municipality would be in a better position to comment on that.
Earlier on Thursday, Etzinger said seven days of heavy rain had left coal stocks wet.
"We have asked our large industrial customers, to reduce their consumption by 10%, but it appears this will not be enough," Etzinger said.