A tube train sized tunnel has started being dug under south London running between Wimbledon and Crayford.

It’s not for trains though, as it’s part of the London Power Tunnels project to upgrade the electricity supply across London, and this new tunnel will be around  20 miles long when completed.

(c) National Grid, London Power Tunnels

This new tunnel follows on from the original London Power Tunnels project, north of the Thames and will replace a maze of cables running under London’s streets which are wearing out and need replacing, but rather than digging up loads of roads, the National Grid has opted for a deep tunnel instead.

Tunnelling was due to start last year, but delayed due to you know what, and today the Tunnel Boring Machine was formally named Edith, to honour Edith Clarke, the first female electrical engineer and pioneer who used maths to improve the understanding of power transmission.

Now it’s been named, it will be lowered down a shaft at New Cross to start digging works in a few days time.

TBM naming ceremony (c) National Grid, London Power Tunnels

In addition to the tunnel, a number of shafts are also needed to be dug down, for access to the electricity tunnels, but mainly for ventilation to keep the cables cool. Once completed, the power tunnel will carry up to 400kV of electricity.


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  1. Paul Parkinson says:

    Do you know if they have published the specific route details?

  2. Melvyn says:

    Wonder if it’s going through chalk or clay given all the dangers anti HS2 brigade claim about damage to chalk aquifers boring HS2 will do !

    The one thing this country excels at is tunnels with even Crossrail tunnels being completed largely on time and budget.

    • Joy Godsell says:

      We have a long way to go before we’re a match for the Swiss and Austrian tunnelers…. :-]

  3. Grant says:

    Interesting stuff. Where is it starting in New Cross? I live about a mile away. World be interesting to take a look.

  4. Ben says:

    The cables only seem to take up a tiny bit of the tunnels, wonder if they can shove something else useful down there

    • Joy says:

      lt would have to be compatible with electricity – as Noel suggests… the mobile phone companies.

  5. Noel says:

    You will most probably find that they will rent out wall space for mobile phone operators as an extra income the same way the railways does

    • ianVisits says:

      The space is needed to dissipate the heat and prevent RF interference between the cables.

      They can’t easily put any other utilities down there as maintenance becomes more of an issue.

  6. Ian says:

    It is a pity that all that heat produced can not be put to good use instead of disappearing up a ventilation shaft into the atmosphere

  7. Uche Mick Chinonso says:

    So this is almost what I had in mind: a railway tunnel between Clapham junction and Lewisham, which would link Battersea with Lewisham calling at Clapham, Brixton, Loughborough Junction, Peckham, Brockley and Lewisham. Imagine if this became reality.

    • Uche Mick Chinonso says:

      If this works, this is how the Bakerloo Line Extension could be achieved more quickly.

  8. David Hanrahan says:

    Is there a gift shop?

  9. Gerard Burton says:

    This would make a nice train route.
    This is a good way of storing power.

  10. James+Reid says:

    Is this the equivalent of the high voltage lines that we see on the pylons across the country?

  11. Lionel Ward says:

    Poor old south London. Finally gets a long tube sized tunnel connect SE to SW and it get filled with lower cables

    Always heard that the clay soil made it hard to dig in the south, seems that where there’s a will there’s a way

    • ianVisits says:

      The clay soil is mostly north London, and lovely to tunnel through – but as the Northern and Jubilee lines in south London shows, it’s not impossible to drive tunnels through south-London, just a lot more effort. South London lacks tunnels more due to the higher availability of mainline trains and lower economic viability for tube trains at the time most of the tube network was constructed.

    • Lionel Ward says:


      I see, interesting. The economic viability aspect seems self-reinforcing. The north grew increasingly dense, and as the economic centre, it was viable to build more and more lines.

    • ianVisits says:

      Other way round – north was already more densely developed – remember most of south London was still fields in the 19th century when the tube lines were being planned to go under already developed urban areas.

      Mainline railways could develop south of the river as they were connecting rural towns across fields. No need to expensively tunnel under the fields.

  12. N Gineer says:

    Sorry to be pedantic but “Once completed, the power tunnel will carry up to 400kV of electricity.” is meaningless. The transmission voltage may be 400kv or 275kv but the actual power transmitted will be XX Megawatts (MW) or even YY Gigawatts (GW)

  13. JP says:

    Presumably it will have a railway in it, a monorail for the engineers to travel on to facilitate maintenance as do others not so very far away over the river.

  14. Paul Burchell says:

    Crayford is not the only tunnelling site they are also tunnelling from Kings Avenue.

  15. PW says:

    Would be good if the heat was recovered through heat pumps and used for district heating, as appears to be in progress for the Underground.
    Another way to reduce the heat would be to use HV DC for the main supply with inverters to AC distribution at surface; this is how most subsea power cables are now designed. DC does not suffer the inductive losses AC does. Sounds like Edison was right after all… to a point. With switching power supplies that don’t need a transformer AC is beginning to look a bit old fashioned, we may yet get LV DC ring mains in our homes for all the electronic gubbins we use these days.

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