When there is insufficient power station capacity to supply the demand (load) from all the customers, the electricity system could become unstable, possibly resulting in a national black-out. To avoid this, Eskom can either increase supply or reduce demand.
To increase supply, Eskom will run its power stations at maximum available capacity. In addition to the coal and nuclear plant, hydro and open cycle gas turbine stations are used at peak times when demand is high.
To reduce demand, Eskom will first call on customer contracts that allow for supply to be reduced or interrupted for specific periods and durations. If this is not enough, Eskom is forced to cut supply to all other customers. This could be done through either Scheduled or Emergency Load Shedding.
During Scheduled load shedding parts of the network are switched off according to a predetermined schedule, with the impact spread equitably over the customer base. Shedding is predictable and allows for customers to plan accordingly.
In exceptional circumstances additional emergency load shedding could be required. Control Centers will shed load using emergency switching in order to protect the network. This will be less predictable and all customers can expect to be affected at any time.
Eskom has recently announced that the pre-emptive load shedding has been suspended until further notice.
For more information about load shedding please visit the Eskom website.