Johannesburg - Eskom has asked large industrial customers to reduce their electricity usage by 10 percent as it seeks to avert a second evening of rolling blackouts.

“Eskom declares an emergency as the power system remains severely constrained,” Eskom said in an e-mailed statement today.

“Any extra load or faults in the system are likely to result in load-shedding.”

Eskom last night started rolling power cuts for the second time this year as generators at two plants failed.

The utility has struggled to satisfy demand for power in South Africa in the past decade, with a lack of working generating capacity forcing Eskom to schedule blackouts for the first time in six years in March to prevent the collapse of the grid.

Eskom is in the process of contacting municipalities to let them know that outages are highly likely tonight, Eskom spokesman Andrew Etzinger said by phone.

Johannesburg City Power asked customers to reduce electricity consumption from 5 pm to 7 pm local time to avoid cuts.

“There is a high probability of load-shedding,” Etzinger said, using the local term for rolling blackouts.

“We haven’t started implementing, but unless something unexpected were to happen, we are heading that way. It is 99 percent certain.”

Industrial customers are complying with the protocol, said Shaun Nel, director of the Energy Intensive Users Group.

“Companies are becoming pretty accustomed to the situation,” he said by phone.

“What’s concerning is the frequency and the magnitude of the outages.”

The City of Tshwane, which includes the capital, Pretoria, said on its Twitter account that Eskom has placed the municipality on standby by for rolling blackouts from 5 p.m. to 9 p.m. today. - Bloomberg News