* Power margins razor thin in Africa's top economy
* Latest crisis triggered by wet coal (Updates with details from media briefing)
By Olivia Kumwenda-Mtambo
JOHANNESBURG, March 7 (Reuters) - South African power utility Eskom said on Friday the power supply remained "constrained but stable" the day after it imposed rolling blackouts for the first time since 2008.
"Should the situation change for the worst, we will declare an emergency at short notice," a spokesman for the state-run utility said, indicating there would be no immediate repeat of Thursday's rolling blackouts.
The latest emergency was lifted on Thursday at around 2000 GMT, as demand from businesses and households eased.
It was imposed after torrential rain soaked power station coal stockpiles. More showers are forecast every day until next Friday around the city of Emalahleni, in the heart of the coal producing and power generation region east of Johannesburg, making a repeat in coming days highly possible.
The 2008 wave of rolling power outages caused misery for millions during an electricity crunch that cost billions of dollars in lost output.
With general elections just two months away, the latest power problem comes at a bad time for President Jacob Zuma and the ruling African National Congress (ANC).
The ANC's governance record is in the spotlight with frequent violent protests erupting in poor black townships over a perceived failure to deliver essential services such as rubbish collection, sanitation and water.
The national power grid has suffered from inadequate investment and construction for years, and now Eskom is in a race against time.
Eskom has been scrambling to build new power stations to ease its razor-thin supply margins, but has been beset by delays at its massive 4,800 MW Medupi plant, which is expected to bring its first units online in the second half of this year.
Underscoring the severity of the situation, Eskom Chairman Zola Tsotsi told a media briefing that even if the new Medupi units had been operating on Thursday, the blackouts would still have been needed.
Chief Executive Brian Dames told the briefing the measures had been required to prevent "a total collapse" of the grid.
Dames said Thursday's crisis had been triggered when Eskom's Kendal power station "received a batch of very wet coal" that could not be fed properly into the system.
This resulted in the grid losing over 3,000 megawatts (MW) in the early hours of Thursday or close to 10 percent of the usual available supply of power.
Eskom's coal stockpiles are mostly kept in the open, in part because of the high cost of storage facilities, and so are prone to damage from heavy rain.
There are storage bunkers available but not enough to protect all the coal. The problem is compounded by most of Eskom's supply coming from exposed open-pit mines. (Additional reporting by Zandi Shabalala; Writing by Ed Stoddard; Editing by David Evans)
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