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The Downing Street problem

AJJewsbury
No, nothing to do with politics - just earthing and bonding - just recent events have perhaps given us an interesting example.


As I'm sure everyone has noticed of late, No.10 Downing Street has a nice electric lamp for its front door - supported by an arch from the iron railings. Similarly, immediately next door to the left (contrary to usual UK practice, designated No.11) also has lights fixed from the railings - two in this case, at least one of which appears to share the same railing system as No.10.


If pictures help: No.10 and No.11


For the sake of this discussion let's assume No.10 and No.11 have separate DNO supplies and the light fittings are all Class I.


If you had to do the design for feeding the lights outside either or both premises (and had no ill-intent to the occupants) what sort of earthing and bonding arrangements would you specify? (and would regulation 714.411.3.1.2 figure in your thinking?)


  - Andy.


Parents
  • 0
    I agree with all of that, and unlike the shared water pipes, being above ground, there is then a small risk of tingles from the railing when feet are on the ground. Actually as the railings are certainly out doors and probably form an electrode anyway, assuming they are in the ground, and if not they could probably be given an earth rod, then you may prefer to just cut the 1mm CPC, supply via an RCD and say it's TT.

    It is  similar to many problems of large areas of earthed and accessible metal outdoors, like the outdoors car charger, but made much worse when you have 2 sources of supply and it forms a parallel diverted neutral path as well.
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  • 0
    I agree with all of that, and unlike the shared water pipes, being above ground, there is then a small risk of tingles from the railing when feet are on the ground. Actually as the railings are certainly out doors and probably form an electrode anyway, assuming they are in the ground, and if not they could probably be given an earth rod, then you may prefer to just cut the 1mm CPC, supply via an RCD and say it's TT.

    It is  similar to many problems of large areas of earthed and accessible metal outdoors, like the outdoors car charger, but made much worse when you have 2 sources of supply and it forms a parallel diverted neutral path as well.
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