Eskom says the electricity system remains constrained with a high probability of Stage 1 rotational loadshedding starting from 5 pm to 9 pm this evening.
The power utility says the load-shedding is a result of protests which continues to impact operations at power stations.
Low coal supplies, wage protests and alleged intimidation of non-striking workers are being blamed.
It says it is asking the CCMA to resolve the impasse on wage negotiations.
Stage 1 requires 1000 megawatts to be shed, 2000 megawatts for stage 2, and so on.
Eskom has asked consumers to conserve electricity, with management saying it will meet with unions this Friday to discuss the deadlock over wages.