Eskom said on Thursday that it has been forced to ramp up power cuts to stage 3 until at least Saturday.
The mechanical replacement of the steam generators in unit 1 of the Koeberg nuclear power station has been completed.
Eskom is examining how the suspension of a pact that enables it to import nuclear fuel components from the US.
South Africa has entered a critical phase of revamping its sole nuclear plant and needs it to run according to plan.
Eskom confirmed that it took the decision to delay taking one of the units at the Koeberg nuclear power station offline on Wednesday due to the energy supply crunch.
The mishandling of the Koeberg life extension project raises serious questions about the capacity of South Africa’s nuclear sector.
Eskom warned that stage-2 cuts could be imposed over the weekend after a unit at the Koeberg nuclear power station had to be shut down.
Emergency evacuation sirens, meant to warn Cape Town residents of a problem at the Koeberg power station, sounded on Thursday – but this was a false alarm.
Eskom has decided not to replace the steam generators at unit 2 of the Koeberg nuclear power station as planned this year over fears it could contribute to winter power cuts.
Energy minister Gwede Mantashe said he suspended a community representative from the board of the regulator because he’s an opponent of atomic power.