No trains south of London during cold weather? Blame a pair of Herberts for choosing the wrong electrical system

Empty Southern lines into Clapham Junction, during a strike. Image: Getty.

As is often the case when the weather is below freezing, commuters around London are having a terrible time this week. The blizzard has hit services on all lines around the capital. Trains running towards the south and southeast have had the worst of it, with services cancelled on Monday before the full impact of the storm really hit.

It’s frustrating to compare the UK’s lack of readiness when extreme weather hits with services in Switzerland or Sweden, which cheerfully run in heavy snow conditions.

It’s also not really a fair comparison: you build a system to deal with the weather conditions you’re expecting, and a Swiss railway that couldn’t handle snow would be useless for half the year. Building southern England’s rail network to Swiss weatherproofing standards would add a lot of extra cost for only a couple of days’ benefit per year.

Some commuters have a much better reason to be grumpy, though. The 750V DC third rail system used on railways south of the Thames is particularly vulnerable to cold. Because of its thickness and relatively low voltage, the conductor rail tends to have ice form on top of it, whether from snow or just moisture in sub-zero conditions. Once there’s an ice layer on the rail, the train can no longer pick up electricity.

Which is a bit of a problem if you want it to go anywhere.

It didn’t have to be this way. In the early 1900s, the London, Brighton and South Coast Railway (LB&SCR) began its electrification programme. It used the latest German technology from AEG to provide a high voltage 6.6kV AC overhead electrical pick-up system – very similar to the 25kV system now used on high speed main lines in the UK and the rest of Europe.

Many of the 25kV systems in use today were converted from similar systems. The electric trains in Glasgow and the ones running out of Fenchurch Street and Liverpool Street in London were converted to 25kV from 6.25kV in the early 1980s, after the quality of electrical insulators improved to allow lower clearance.

High voltage overhead electrification is cold-resistant; it’s what the Swiss and the Swedes use for their systems. Snow tends to fall off the narrow overhead wires, they run hot enough to avoid icing, and the high voltages involved make it easier for the train to pick up power.

It’s also better in general: the higher voltage makes power distribution more efficient, with fewer expensive substations required. The pickup design allows overhead electrified trains to run at up to 400km/h, compared to just 160km/h for third rail trains. Since 1956, 25kV overhead electrification has been specified as the only system allowed for new mainline railway electrification in the UK.

A map of the LB&SCR network, at Victoria station. Click to expand. Image: Oxyman/Wikipedia.

By 1913, the LB&SCR’s high voltage overhead electric lines stretched from Victoria and London Bridge to much of outer south London, covering what is now the Southern Metro network. The company was preparing to electrify the main line to Brighton and the Sussex Coast – effectively the whole present-day Southern rail franchise.

But World War I disrupted equipment supplies and used up manpower, putting electrification on hold. Then came 1921’s ‘grouping’, in which all the commuter railways south of the Thames were combined into the Southern Railway.

Unfortunately for today’s commuters, the Southern Railway wasn’t interested in the overhead system. The merged company’s general manager was Herbert Walker, who had previously run the London & South Western Railway (L&SWR), which had just electrified its own suburban tracks using the low-voltage DC third rail system.

Walker and his chief electrical engineer, Herbert Jones (Herbert was a popular name in the Edwardian railway industry, apparently) picked up their experience of electric railways in the USA, where commuter lines used DC third rails. While the LB&SCR was electrifying its London lines with the German-derived high-voltage AC overhead system, the L&SWR did the same with low-voltage DC.

This had the advantage of being cheaper to install, avoiding the need to build supporting pylons and their foundations. It also allowed the L&SWR to run up a greater length of electrified track faster than its neighbour, despite being otherwise inferior. 

The new Southern Railway needed to electrify its whole network: steam trains couldn’t support the high-intensity commuter operation that it needed to become. And it needed to adopt a single system rather than have complicated switching or incompatible routes. So, although ex-LB&SCR managers lobbied to roll out their system across the network, the Herberts’ pet project unsurprisingly won out.


By 1929, the last AC train ran on the Southern Railway. The masts were unceremoniously torn down and replaced with third rail. Subsequent electrification south of the Thames was also carried out using third rail, continuing through the British Rail period as late as 1988, despite the ban on ‘new’ third rail electrification. 

And so, trains in the south still run slowly all year round, and not at all when it’s icy.

In the long run, there may be hope for commuters. Former Network Rail head of electrification Peter Dearman (now at engineering consultancy Bechtel) says that there is no long-term future for third rail for speed and efficiency reasons, and the Office of Rail Regulation believes it is unsafe for track workers. The current electrification programme includes a pilot scheme to convert the third rail between Basingstoke and Southampton to overhead AC.

But given the delays to the Great Western electrification and the government’s recent cancellation of multiple add-on electrification projects, it doesn’t seem likely that southern commuters will see the return of the LB&SCR’s AC masts any time soon. And the best plan for icy days will still be to work from home, well beyond the 100-year anniversary of the Herberts’ botched job.

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The mountain in North Wales that tried to stop the UK’s blackout

Elidir Fawr, the mountain in question. Image: Jem Collins.

Last Friday, the UK’s National Grid turned to mush. Not the official term perhaps, but an accurate one after nearly one million people were left without power across the country, with hundreds more stranded at train stations – or even on trains (which isn’t nearly as fun as it might immediately sound). 

Traffic lights stopped working, back-up power failed in hospitals, and business secretary Andrea Leadsom launched an investigation into exactly what happened. So far though, the long and short of it is that a gas-fired power station in Bedfordshire failed just before 5 o’clock, followed just two minutes later by Hornsea offshore wind farm. 

However, amid the resulting chaos and inevitable search to find someone to blame for the outage, a set of mountains (yes, mountains) in North Wales were working extremely hard to keep the lights on.

From the outside, Elidir Fawr, doesn’t scream power generation. Sitting across from the slightly better known Mount Snowdon, it actually seems quite passive. After all, it is a mountain, and the last slate quarry in the area closed in 1969.

At a push, you’d probably guess the buildings at the base of the mountain were something to do with the area’s industrial past, mostly thanks to the blasting scars on its side, as I did when I first walked past last Saturday. 

But, buried deep into Elidir Fawr is the ability to generate an astounding 1,728 megawatts of electricity – enough to power 2.5 million homes, more than the entire population of the Liverpool region. And the plant is capable of running for five hours.

Dubbed by locals at the ‘Electric Mountain’, Dinorwig Power Station, is made up of 16km of underground tunnels (complete with their own traffic light system), in an excavation which could easily house St Paul’s Cathedral.

Instead, it’s home to six reversible pumps/turbines which are capable of reaching full capacity in just 16 seconds. Which is probably best, as Londoners would miss the view.

‘A Back-Up Facility for The National Grid’

And, just as it often is, the Electric Mountain was called into action on Friday. A spokesperson for First Hydro Company, which owns the generators at Dinorwig, and the slightly smaller Ffestiniog, both in Snowdonia, confirmed that last Friday they’d been asked to start generating by the National Grid.

But just how does a mountain help to ease the effects of a blackout? Or as it’s more regularly used, when there’s a surge in demand for electricity – most commonly when we all pop the kettle on at half-time during the World Cup, scientifically known as TV pick-up.

The answer lies in the lakes at both the top and bottom of Elidir Fawr. Marchlyn Mawr, at the top of the mountain, houses an incredible 7 million tonnes of water, which can be fed down through the mountain to the lake at the bottom, Llyn Peris, generating electricity as it goes.


“Pumped storage technology enables dynamic response electricity production – ofering a critical back-up facility during periods of mismatched supply and demand on the national grid system,” First Hydro Company explains.

The tech works essentially the same way as conventional hydro power – or if you want to be retro, a spruced up waterwheel. When the plant releases water from the upper reservoir, as well as having gravity on their side (the lakes are half a kilometre apart vertically) the water shafts become smaller and smaller, further ramping up the pressure. 

This, in turn, spins the turbines which are linked to the generators, with valves regulating the water flow. Unlike traditional UK power stations, which can take hours to get to full capacity, at Dinorwig it’s a matter of 16 seconds from a cold start, or as little as five if the plant is on standby.

And, designed with the UK’s 50hz frequency in mind, the generator is also built to shut off quickly and avoid overloading the network. Despite the immense water pressure, the valves are able to close off the supply within just 20 seconds. 

At night, the same thing simply happens in reverse, as low-cost, surplus energy from the grid is used to pump the water back up to where it came from, ready for another day of hectic TV scheduling. Or blackouts, take your pick.

Completed in 1984, the power station was the product of a decade of work, and the largest civil engineering project commissioned at the time – and it remains one of Europe’s largest manmade caverns. Not that you’d know it from the outside. And really, if we’ve learned anything from this, it’s that looks can be deceiving, and that mountains can actually be really damn good at making electricity. 

Jem Collins is a digital journalist and editor whose work focuses on human rights, rural stories and careers. She’s the founder and editor of Journo Resources, and you can also find her tweeting @Jem_Collins.