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A blackout is when there’s a total loss of electrical power. It is caused by an imbalance between power generation and consumption. Blackouts can last for just a few minutes or in the worst-case scenario stretch into several hours, days, or even weeks. 

Electricity blackouts are caused by a range of factors: 

  • Extreme weather: strong winds take down trees that knock out transmission lines, snow and rain cause flooding can damage substations and other infrastructure, not to mention making it difficult for engineers to fix.  
  • Large-scale accidents & systems failures: such as software crashes, component faults, fires, explosions, and basic human error. 
  • Infrastructure attacks: substations can be damaged by vandals or thieves trying to steal copper, while terrorists can target them using bombs or other physical weapons 
  • Space weather: Sun-based phenomena such as geomagnetic storms, solar flares, and meteors can have a devastating impact on satellites and electrical infrastructure. 
  • Cyber-attacks: modern energy networks are shifting to decentralised smart grids. This greater emphasis on connectivity increases cybersecurity vulnerabilities.  


The damage a blackout causes to electrical equipment and networks depends on the timing. If the system is idle when the power goes out, it’ll probably be OK when the power comes back on (although there is the risk of a power surge). 

However, if power fails when you’re saving work or in the middle of a process or operation, it’ll likely cause a problem. That's where uninterruptible power supplies come in, providing all-important backup power to prevent damaging downtime and data loss.

Read our special in-depth investigation the Blackout report to learn more about the issue of power cuts in the UK. And learn about some of the biggest and longest blackouts in history.



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