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  • Random electricity pylon transformer question!
  • meeeee

    Was camping at the weekend and while waiting for the wife to stop faffing I started looking at this pylon

    Hopefully pic will work!

    But why does the insulated cable come out the ground, then become bare wire, then into the transformer and finally back into the ground?

    Why does it lose the orange insulation (assuming that’s the bit going into the transformer) and why not just stick it all on the ground?

    Wife now thinks I’m even stranger than befoe9 for wondering these things and taking a picture of it.

    I know nothing about the grid electrical system. In the classic STW style, that’s not going to stop me having a go.

    At a guess, I’d say if it was underground it would be more difficult to keep it dry, cool, and serviced.


    why not just stick it all on the ground?

    The moles would get at it.

    Premier Icon TheGingerOne

    You need to wait for Onzadog to find this thread and educate you


    So basically it would get red hot, melt through the earth to Australia and we’d be overrun with giant electrified mutant super moles!

    I love STW I knew you’d have the answer, my 4yr old will love that as she was also asking me why I was taking the photo!


    Red cable in ground insulated,from moisture and damage, red for electrical cable,

    bare conductors above ground so they can be seen easily if damaged, to reduce heat build up and so as not to need seperate insulation on each feed, not on ground for safety although some are in caged pens, which require a base, planning permission,a fence, and lots of signs,but you still need the pole, to support cables, so why not bung a transformer up there out of the way.

    oh and its not a pylon its a pole mounted transformer.

    It looks like an 11kv/415v 3 phase pole mounted transformer.  Maybe 500KVA.  It could be historically that the site was fed via an overhead pole route and the orange/red cable is a new underground supply feed.  It could be easier to stick the transformer up on a pole to get it out the way than build a compound for it (space issues).

    Premier Icon igm

    Inverted pole equipment – probably a 200 or 315kVA.

    The red cable is 11kV. The black 400V.

    The transformer is designed for open wire HV connections so you can’t terminate the 11kV cable on to it.

    Basically it is a cheap way of putting a substation on to an underground network.  Circa £10k instead of £30-50k for a ground mounted substation.


    igm pretty much beat me to it.  Transformers are either ground mounted or pole mounted and due to the connections, you can’t mix and match.

    Sometimes, you need to connect a cable, rather than an overhead line to a pole mounted transformer like the one in your picture. There needs to be a point where underground network connects to overhead network and here, it happens just before the transformer.

    It may be that this location used to be fed by over head lines. Either because of price or permissions, the overhead line might have been replaced but they couldn’t/wouldn’t/didn’t build a ground mounted substation.

    It’s actually a pretty common arrangement and found on a lot of rural networks.


    Thanks, this place is great for answering questions that although seem simple to people who know the answer,  are a puzzle to the average man who is just curious as to how things work!

    My daughter will be a bit disappointed about my mole theory being wrong though.  Maybe I won’t tell her the truth just yet…

    Premier Icon cp

    Makes you wonder though…. What’s in that shed to need its own transformer?! 😉

    Premier Icon maccruiskeen

    But the real question is – what does it transform into? Theres maybe more than meets the eye.

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