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Last Updated: Friday, 15 August, 2003, 13:10 GMT 14:10 UK
What caused the blackouts?

Years of under-investment by power companies have left behind a US electricity grid that is woefully inadequate to meet increased demand.

Candlelit dining
The whole purpose of having an inter-linking grid is to ensure that, should one area have a problem, neighbouring areas can easily send some extra power in that direction.

What caused the initial problem is still in dispute.

But something knocked out power near the Canadian border and the system began to demand power for other areas.

However, in this case, the neighbouring areas simply did not have any spare electricity to help out.

And, far from being able to solve the problem, the extra demand caused each neighbouring area to fail in turn, causing a domino effect.

That left millions of people without power, as the crisis spread from New York to Detroit, and Toronto to Ottawa.

Third-world conditions

"We're a superpower with a third-world grid," former energy secretary Bill Richardson told CNN television.

Click here to see a map of the north American electrical grid

Ironically, much of the third world would have coped better with the failure since far more services and business have back-up generators as a matter of course.

"The problem is that nobody is building enough transmission capacity," Mr Richardson explained.

Demand for electricity in the US has been growing steadily, alongside increased use of air conditioning and computers.

But electricity firms have not been investing in building new lines able to transmit high voltages.

US power demand has surged by 30% in the last decade, while transmission capacity has grown by just 15%.

Bottlenecks

That has meant that many of the electricity lines are running very close to their limits, especially when extreme weather sets in.

And several high-voltage transmission lines are already regularly jammed up especially in the New York area.

These bottlenecks make the whole system much less responsive to extra demand or excess capacity in different regions, making it more difficult for different areas to help each other out.

The government used to take responsibility for ensuring that each area had enough spare capacity to act as a safeguard in times of difficulty.

But, since the deregulation of the industry in the 1980s, the rules have been much less strict.

The Enron effect

Furthermore, the increased competition amongst power suppliers has cut profit margins, making the firms reluctant to make new investments if not absolutely necessary.

"The problem is that electrical transmission systems are a lot like schools for politicians - it's very easy to defer maintenance on them until things fall apart," said Pers Peterson of the University of California, Berkeley.

"We have a transmission infrastructure that has had very poor investment and is in a degraded condition," he warned.

The Enron affair has also had a negative effect by weighing heavily on the share prices of power suppliers.

That has left the firms with less cash to invest in maintenance and upgrades.

Technical trouble

Although the lack of investment is the underlying problem, experts say there must have also been some technical fault which failed to stop the domino effect.

The precise cause of the power failure is not known.

But the problem area should have been isolated rather than allowing the lights to go out in each region in turn.

Some experts blame this on a computer failure, while others say people at control centres should have been able to trip the necessary switches to stop the problem escalating.

Either way, the shortcoming served to prove just how close to the edge of its limits the whole of the US electricity grid is.




WATCH AND LISTEN
The BBC's Fergus Walsh
"The biggest consumers of power in the world"



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