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Emergency Power Cuts

Load Shedding

Load shedding is a form of emergency power cut which is used by energy companies in response to severe shortage of electricity generation in Northern Ireland.

Load shedding is used to reduce electricity consumption by switching off the power supply to groups of customers. It is a last resort method of protecting electricity supply when the entire system is at risk.

It is only used in rare, exceptional circumstances but is recognised globally as a standard method of balancing electricity supply and demand.

Read more about load shedding in the following Frequently Asked Questions.

  • What causes Load shedding to happen?

    It is the responsibility of the System Operator Northern Ireland (SONI) to keep the electricity system “balanced” - enough electricity generated to meet customer demand.

    The balance of the electricity system could be at risk if there is a shortage of electricity supply. A number of other factors can impact the balance including extreme weather and planned or unplanned infrastructure outages. To restore the balance, the System Operator Northern Ireland (SONI) will instruct NIE Networks to reduce load for a period of time – this is called load shedding,

    It's important to note that load shedding is different to planned local outages, such as for maintenance, and unplanned outages caused by damage to wires and cables for example during storms.

  • How does it work?

    SONI decides when load shedding is needed in Northern Ireland.

    Before it turns to load shedding, SONI has other measures it takes to try to overcome a power shortfall, such as importing more power from other regions such as Scotland and the Republic of Ireland. 

    It can also appeal to consumers to voluntarily reduce their energy consumption — for example by postponing their use of dishwashers and washing machines or asking industrial electricity users to power down for a period of time

    But after exhausting these options, if it still needs to reduce demand, SONI will instruct NIE Networks to carry out load shedding.

    SONI will confirm how much power needs to be saved, and then NIE Networks will work out how to achieve those reductions.

    NIE Networks has a plan for how load shedding should be carried out, including a schedule or a “rota” for the sequence in which particular loads will be shed and restored.

    The plans are drawn up by specialist engineers within NIE Networks. The plans can then be implemented immediately when a load shedding event occurs.

    This plan seeks to spread the inconvenience equitably: a limited disruption to many, rather than more significant disruption to a smaller number of customers.

  • How is the rota devised?

    Each postcode area across Northern Ireland is split into 18 blocks which are each made up of a number of discrete geographical areas.  Each of these blocks is assigned a letter between A and U. The letters F, I and O are not used.

    Each day of the week is split into a number of three-hour slots. The first planned slot of the day starts at 07:00 and the last slot ends at 00:00. If possible load shedding would not happen overnight as the system demand should naturally be much lower, however if required the three-hour slots could continue between 00:00 and 07:00.

  • How does NIE Networks decide whose power gets disconnected?

    NIE Networks will disconnect certain areas from the power supply by switching off the substation serving that area.

    A substation could supply anywhere from a few hundred to many thousands of customers.

    Which substations get switched off depends on a number of factors, including how much power needs to be saved.

    This decision is made by specialist NIE Networks Control Engineers.

  • Are there special arrangements in place for critical customers (hospitals) or to protect critical infrastructure (sewerage, pumping stations, traffic lights)?

    A very limited number of sites are protected from emergency power cuts triggered by a civil emergency as set out in the Electricity Supply Emergency Code (ESEC). ESEC enables an equal distribution of electricity supply to customers as far as reasonably practicable, whilst ensuring that pre-designated “Protected Sites” maintain supplies for as long as possible.

    Protected Sites are typically locations which are deemed to be critical national infrastructure, such as air traffic control centres and major hospital facilities with accident and emergency departments.

    Organisations which are not already aware of their protected status will need to apply to become “protected” as this is not automatic. There are very strict qualifying criteria set out by the Government, and more information on this is provided via the ESEC procedures.

    To apply, the Application Form should be completed and sent to for NIE Networks to review.

    It is important to note that residential customers, including those on our Medical Customer Care Register and businesses without backup generation and which are not listed as “protected” by the government, would not be exempt.

    It is important to note that the actions described in ESEC are not used to handle sudden shortfalls in generation, or to deal with day-to-day repair and recovery of faulty or damaged parts of the transmission and distribution networks. During such events, sites included on the protected sites list may well still experience interruption to their electricity supplies

  • How do I know if my power will be switched off?

    If load shedding is necessary in your area, you may not get any advance warning as NIE Networks may only be given short notice by SONI that load shedding is required.

    However, NIE Networks will give customers as much notice as possible, as the circumstances allow.

  • How will you provide updates to customers in an event?

    A range of communications methods will be available.

    We will publish information on the NIE Networks website (, our social media platforms as well as informing local media outlets. Alternatively contact our helpline on 03457643643 for information.

  • How long will I be without electricity supply? Can the load shedding times be negotiated?

    Each block will be disconnected for a maximum of three hours at a time. The blocks are also rotated, so that once an area has been taken off supply, that block goes to the bottom of the list so all blocks are used in rotation before that block is used again.  Unfortunately, we cannot negotiate and arrange alternative times at an individual customer level.

  • How will I know which block my postcode is in?

    Your block letter is static and will not change during an emergency. It is based on where you live and how your electricity is supplied. In an event, we will publish block letters on our website.

  • How often will I be switched off?

    The electricity supply will be turned off to certain areas, or blocks, for three hours at a time, depending on the shortage of electricity. This could be affected by the weather, the time of day and the demand for electricity. Where practically possible, you will receive notice of load shedding being introduced.

  • My power has gone off at a time different to those published, why is this?

    The timing of the rota disconnections can change. If the situation deteriorates, NIE Networks may have to begin the rota earlier than originally required. If the situation improves, NIE Networks may be able to reduce the number of blocks affected or the duration of the disconnections.

  • What do I do if my electricity does not come back on when I expect it to?

    If your electricity supply has not been restored after four hours, please contact our helpline on 03457643643.

  • What about customers with medical needs?

    Customers who have signed up for the Medical Customer Care Register should contact our helpline on 03457643643 for advice from our specially trained team. Alternatively, information will also be available on the NIE Networks website (

  • How do we tell the difference between an electric fault and load shedding?

    It is important to determine if your interruption to supply is caused by the load shedding event or a network fault. Please visit the NIE Networks website ( or contact our helpline on 03457643643 for information on the areas affected by load shedding. If your area is not included in the load shedding please report this as a fault.

  • What advice do you have for customers during a load shedding event?

    When the power goes off, switch off electric heaters and cookers to avoid a fire risk when the power is restored.
    It’s always best to switch off and unplug equipment, including satellite receivers, televisions and computer equipment, but leave a light on to tell when the power is restored. It may help if you can turn off your central heating time switch while the electricity supply is off.

    • Check on elderly or vulnerable neighbours, family and friends and make them aware of the electricity supply interruption situation.
    • Listen out for information on local radio, check our website or social media platforms, or call us on 03457643643.
    • Fill a vacuum flask with hot water boiled in the kettle and recharge mobile phones and rechargeable batteries for torches before the supply goes off.
    • Cordless phones don’t work without electricity, so consider having a basic telephone in case of emergencies.
    • Keep fridge and freezer doors closed. Contents should be safe for many hours but, if in any doubt, dispose of the food if it appears to have defrosted.
    • To keep warm, stay in one room, or even in bed, and remember gas and oil central heating boilers generally won’t work without electricity to power their pumps.
    • When using an alternative form of heating or lighting - use it safely.
    • It may be necessary to adjust time switches and clocks when your power returns.
    • Back up your computer work before the power is expected to go off.
    • A battery back-up alarm clock may be useful for any overnight or early morning power interruptions

    We realise that a reliable electricity supply is crucial for our business customers. However, power cuts can happen and often they are due to situations out of our control. Business owners should think about risks to your business if you experience a power cut.  For example, consider your manufacturing processes, refrigerated items, data access, telephone lines, customer orders, accessing your building maintaining, key business processes that may be impacted by a power cut. Have you plans to manage staff wellbeing as water supply and gas may be affected by a power cut?  Can staff work from an alternative location? Would a back-up generator help and if you already have one, has it been serviced recently? It is worth having a plan in place and being prepared in the unlikely event of a power cut.