Power Cuts by Network: How Reliable Is Your Electricity Supply?

When the lights go out, most people think about their energy supplier. Their energy supplier has nothing to do with it.

The wires are run by a distribution network operator, decided entirely by where you live, and Ofgem measures how well each one keeps the power on. This page is those figures: how often supply was interrupted, for how long, and how each network did against the target it was set.

Your supplier does not run your wires

Britain’s electricity system splits the job in two. Your supplier sells you the energy and sends the bill. A separate company owns the cables, substations and poles that physically deliver it, maintains them, and turns out at three in the morning when a storm brings a line down.

There are fourteen distribution licence areas, run by six groups. You cannot choose yours and you cannot switch it — it is a regulated monopoly, which is precisely why its performance is measured and published. Competition disciplines your supplier; for the network, this data is the substitute.

It also means a power cut is not a reason to change supplier. Moving from one supplier to another changes who bills you and nothing about the wires. If you want to compare the companies you can choose between, that is our supplier complaints data and our supplier reviews.

The two measures, and why there are two

Ofgem publishes reliability as a pair, because one number on its own would hide the thing you actually care about.

• Customer Interruptions counts power cuts per 100 customers over the year. It measures how often supply fails.
• Customer Minutes Lost counts the average minutes a customer spent without power. It measures how long failures last.

A network could score well on one and badly on the other, and that tells you something real. Many brief interruptions suggest a system that faults often but restores quickly, usually by switching supply around an interconnected network. Few but lengthy ones suggest faults are rare and hard to reach when they happen. Only the pair distinguishes them, which is why nothing here combines the two into a single score.

One misreading is worth heading off: an interruptions figure of 40 does not mean 40 per cent of customers lost power. It is 40 interruptions per 100 customers, and one unlucky customer interrupted four times contributes four of them.

How each network performed

Both tables are sorted best first. Every figure is measured against a target set for that licence area, and Ofgem’s own red, amber and green rating is shown as given rather than recalculated here.

Why the targets differ by area

Each network is set its own target, and that is the single most important thing to understand before reading the tables as a league table.

Holding a Highlands network to the same standard as inner London would be meaningless: one runs overhead lines across mountains and moorland, the other a dense underground network where an engineer is never far from a fault. Ofgem therefore sets targets that reflect what each network is working with, and rewards or penalises it against its own.

So there are two different questions on this page, and they have different answers. Which network is most reliable? is the actual figure. Which network is doing best with what it has? is the variance against target. A rural network can miss the first badly and comfortably beat the second, and that is not a contradiction.

The targets also tighten over the price control period, so holding a figure steady counts as falling behind. That is deliberate: the scheme is designed to buy improvement, not maintenance.

Geography explains most of the spread

The gap between the best and worst networks is large, and most of it is not about competence.

Overhead lines fail far more often than underground cables. They are exposed to wind, lightning, ice and falling branches, and every one of those is more common in open country than in a city. Rural networks are also long and thinly meshed, so there is often no alternative route to switch supply through, and the repair crew has further to travel to reach a fault that took longer to locate.

Urban networks are the reverse: mostly underground, heavily interconnected, and short. A fault is often restored by rerouting within minutes while the cable is repaired at leisure. That is why the most reliable areas on this page are consistently the densest ones, and it says more about cable depth than about management.

Weather is the other driver, and it is why a single bad year is weak evidence. One major storm can dominate a network’s figures for a whole year. Ofgem makes allowances for exceptional events, but the honest way to read reliability is as a trend across several years rather than a verdict on one.

What actually causes power cuts

Everything above says how often supply failed and for how long. None of it says why, and why is what most people are actually asking after a bad fortnight.

Network operators report every fault to Ofgem with a cause attached, under a scheme called NaFIRS. Three of the six publish that return as open data, and it gives a straight answer to a question most people get wrong: the largest single cause of lost supply is not weather. It is the network’s own equipment wearing out. Deterioration through age or wear is the top cause at all three of the operators that publish, ahead of wind, trees, lightning and anything a third party did with a digger.

That fits the geography above rather than contradicting it. Overhead rural networks fault more often than urban underground ones, and what fails on both is mostly old kit — the weather decides how much worse a bad year is, not what the ordinary year is made of.

Three warnings before the figures. This covers three networks of six and five licence areas of fourteen, so it is not a Great Britain picture and nothing here should be read as one. The numbers are raw sums from the operators’ own returns and are notthe Customer Interruptions figures in the tables above, which are per 100 customers and adjusted — the two must not be compared. And each operator reports in its own words, so the causes are listed separately rather than merged into one league table of causes.

Satisfaction is a different question

Ofgem also surveys the people who have actually dealt with their network — after a power cut, a new connection or an enquiry — and scores each one out of ten.

It is worth keeping separate from reliability, because it measures something else: not how often the power failed, but how the network handled it when it did. Being told what is happening and when it will be fixed changes the experience of an outage a great deal, and a network can be good at that while still having more outages than most.

Two cautions on reading those scores. They sit in a narrow band near the top of the scale, so the gap between first and last is far smaller than it looks in a ranking — a table of positions exaggerates differences of a tenth of a point. And the survey only reaches customers who made contact, which is a particular group: it says nothing about the majority who never needed to.

What this means for you

You cannot change your network operator, but this data is still worth something.

If you are choosing where to live and depend on a reliable supply — working from home, medical equipment, running a business — the figures for an area are a genuine input, and the gap between the best and worst is not small.

If your supply is already unreliable, two things are worth knowing. Your network operator, not your supplier, is who to contact about power cuts, and 105 reaches yours from anywhere in Great Britain. And Guaranteed Standards of Performance mean you may be owed a fixed payment when restoration takes longer than the rules allow — those claims also go to the network operator.

It is also worth adding yourself to the Priority Services Register if you are of pension age, disabled, chronically ill or have young children. It is free, and it tells the network who to reach first when supply is lost. Our energy debt and support page covers what else the register does.