Johannesburg - The city of Johannesburg said on Tuesday power utility Eskom's abrupt resumption of rotational electricity cuts on Sunday to ease pressure on the national grid took it by surprise, leading to confusion where entire substations were load-shedded at once instead of block-by-block.

"This happened as a result of the City Power system control using a different version of the schedule compared to what Eskom used after the system crashed," the city said in a statement.

"This system has since been aligned with the Eskom system."

City Power was established in 2001 as an independent municipal entity wholly owned by Johannesburg to provide electricity to residents through Eskom.

Struggling Eskom said on Tuesday it would implement rolling blackouts for a third straight day, taking 3 000 MW off the load at any given time to avoid a total collapse of the grid. The utility had last implemented the emergency measure in early December.