9 facts you need to know about brownouts

In some instances, power companies will instigate a brownout on purpose, as rationing electricity supplies can alleviate the strain on the power grid. An intentional reduction in voltage can be a common strategy to address extra strain on the grid. For example, in hotter countries where air conditioning places a strain on the system during the height of summer, brownouts are a common tactic.

A brownout may be used as an alternative to a rolling blackout, whereby power is completely interrupted in an organised way, but staggered across different areas to buy time to stabilise the grid.

In the UK, you might be forgiven for thinking that brownouts belong in the 1970s, but they’re relatively frequent occurrences. The National Grid has to maintain an electrical frequency of 50Hz. When supply falls and demand remains high, the frequency drops below this level. Beyond intentional incidents that aim to avoid complete blackouts, brownouts can result from various faults in the transmission and distribution networks, faults in the connected equipment or high inrush and switching currents in the customer’s installation.

Although the normal voltage for homes in the UK is 230 volts, it isn’t constant, so the voltage at an individual property will vary, based on power usage and whether the power supply network is operating normally. While networks are designed to keep the voltage in the permitted tolerance or statutory limits, exceptional circumstances such as a fault somewhere on the network can mean that the operator has to supply a voltage outside the normal limits, sometimes using an alternative source of power to keep the power supply running.

Computers and televisions may shut off or malfunction during a brownout as the voltage level reduces. Unfortunately, any fluctuations in power, whether up or down, can result in permanent damage to electronic devices. Electrical equipment, from TV set-top boxes to computers and wifi routers, can crash, freeze or undergo damage at lower voltages. If there’s no advanced power back up or supply, the sensible decision is to unplug computers, TVs, printers, routers and mobile phones and other sensitive equipment, as well as any devices that are charging.

While a lot of machinery will simply fail to function if it doesn’t have enough energy provided to it, some electrical items – particularly the older ones – can malfunction. During a brownout, it’s a good idea to turn off heavy power users with motors at home, such as washing machines, dryers and dishwashers. While network operators might advise that manufacturers of electrical equipment design their products to cope with variations in current, it’s best not to make any assumptions.

An induction (or asynchronous) motor will draw more current to compensate for the decreased voltage – this can then lead to overheating and burnout. If a substantial part of a grid’s load is electric motors, reducing the voltage may not actually reduce load and can result in damage to customers’ equipment.

During a brownout, a drop in voltage can mean that control signals fall below the level that logic circuits can detect reliably and accurately. When the voltage returns to normal levels, the logic can latch at an incorrect state; it’s possible that even a ‘can’t happen’ state could occur. Because of this phenomenon, a brownout could even cause a motor to start running in reverse.

Even a relatively small reduction in voltage will affect how much heat a resistance device like an electric space heater can give out quite considerably – meaning that a brownout can impact the heating in one’s home.

Lights may dim and flicker on and off during a brownout, but this shouldn’t result in any problems once the power returns to its normal level. For example, an incandescent lamp will dim due to lower heat creation in the filament and lower conversion of heat to light. Usually, this won’t cause any lasting damage, but the lamp’s functionality will be affected for as long as the brownout lasts.

When using a computer, if there’s a loss of power any write operation in progress at the time is terminated partway through. Consequently, any unsaved data, including open documents and databases may well be lost. For businesses, this means that offsite data backups are really important, as is having an uninterruptable power supply (UPS) to buy some extra time to save files or data and shut down computers properly if there is a prolonged power dip. You can get some tips on how to prevent data loss here.

What if electrical equipment gets damaged as a result of a brownout? Can consumers get any compensation? According to one DNO: “As most power cuts are outside our control unfortunately we’re not liable for any loss or damage.” While damage to home equipment may be covered by home insurance, householders will need to get their network operator to confirm details of the brownout to make a claim.

Now that you know about the effects of brownouts, you can find out more about the many challenges of maintaining a reliable power supply by reading our ebook Keeping Your Lights On.