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A brownout happens when the voltage drops below the usual mains supply level. It is similar to a sag – a short-term drop in voltage – but can last for anywhere between a few minutes or even several hours and days.  

Brownouts tend to be caused by increased demand for power or extreme weather conditions putting additional strain on the electricity network.  

Sometimes, brownouts can be initiated intentionally. This occurs when National Grid deliberately reduces voltage to ration electricity supplies and prevent a possible blackout. 

Tell-tale signs of a brownout include flickering lights, electrical appliances quickly switching off and turning back on again, and intermittent internet connections.  

Brownouts are damaging for IT loads – in many ways they can be more disruptive than a total blackout, when the power simply goes off. During a brownout, devices continue to receive power but at a reduced level. This can cause some devices to malfunction. 

Uninterruptible power supplies can handle the reduction in voltage due to its input voltage window. When the voltage drops outside this window, the UPS’s batteries kick-in and take over without any disturbance to the load. 

Learn more about power problems such as brownouts, sags, and surges with our ‘UPS Basics’ video: 

 

Further reading: