Johannesburg - Eskom has declared a power emergency and requested industrial users cut consumption by at least 10 percent today.

The demand is in place until 9 p.m. after four generating units went down during planned maintenance earlier today, Andrew Etzinger, a spokesman for the Johannesburg-based utility, said by phone.

The request was made under the so-called declaration of emergency protocol that was agreed with users in 2008.

“Eskom calls on all customers to reduce electricity usage,” the company said in a statement.

“We are hopeful that by applying these measures, coupled with support from all electricity consumers, we will achieve the required load reduction necessary to protect the national grid.”

The local units of ArcelorMittal, BHP Billiton Ltd. and Glencore Xstrata Plc are among the 32 companies that are members of the country’s Energy Intensive Users Group that can be called on to reduce usage when Eskom’s reserves are running low.

The utility is spending 500 billion rand to replace aging equipment and add plants to avoid the blackouts that affected South Africa in 2008.

Eskom’s reserve margin is “virtually zero,” Etzinger said.

“We have all our generators running at full capacity and at the moment we’re able to meet demand. But recognising demand will increase by 1,500 megawatts as we go into this evening’s peak, that would make us vulnerable.”

Eskom asked large customers to “voluntarily cut” by as much as 30 percent, Shaun Nel, a director at the Energy Intensive Users Group, said by phone.

“Members can do it voluntarily for a while, but at some stage there has to be a more equitable share of the burden.”

Large customers have cut usage by 1,000 megawatts since earlier this week, he said. - Bloomberg News