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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.


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    I don't see why the whole street should not be on one DNO supply, but each address could be on a separate phase. There may be special rules for the Whitehall estate. If the railings are continuous with the lamp supports then wouldn't they simply be earthed as exposed conductive parts?


    Did you notice what appears to be a waterproof commando connector on the end of a bit of SWA to the left of no. 10's front door? I assume that is what is currently powering the Christmas tree lights.
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    Same as you do when houses share a common water main but are on different substations - both will be bonded, the unusual thing here is that it is visible, but an equivalent connection exists in every housing estate large enough to support more than one substation.

    I strongly suspect that in this case however, there is also more than one source of supply to no10 alone. If the outside lights are backed up or not I do not know, but I'd expect a at least some of the equipment to be worth keeping on during a power cut.
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    I would think that no 10 and11 would have a 3 phase supply think of all the computer and security kit inside
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    I would wire the outside lights in accordance with normal practice, incorporating a CPC as with any class 1 light.

    I would consider a bonding conductor in addition between the metal fence and the MET of each property. If the two fences are not reliably continuous, I would also bond the two fences to each other.
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    46295262e54caf47348a0bfa9f6f6a80-huge-img-20140115-00048---copy.jpg


    I did not see any warning signs.


    Clive
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    Perhaps the lamps are Class 2


    or


    Isn't it just a fancy lamp post?
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    geoffsd:


    Isn't it just a fancy lamp post?




    No, it’s Clive.


    I visited Downing Street a few times before the gates went up, the last time was not long after I met my future wife, we just parked her Mini in Whitehall and walked in.


    I have been twice since the gates went up and you have to make an appointment, the last time I actually visited was as a registered helper of the Girl Guide Association and I stood by the door with the Girl Guides and their leaders wearing a Girl Guide baseball cap whilst a policeman took photos for us. After we got back out through the gates one of the dads announced he had left his bag behind and sure enough his rucksack was slap bang in the middle of Downing Street “being monitored”, the dads were more trouble during the day than their daughters!


    The idea that there may be a risk of electrocution due to how the lights are wired never entered my head.


     Andy B.


     

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    I remember the days when one could simply walk into Downing St. And there were none of those innocuous bollards, whose roots (I have seen them being installed) extend further than you would think.


    Yes, I think that the risk of electrocution would be the least of one's worries. ?
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    There's a policeman stood outside 24/7 and the buggers still get out to cause chaose
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    Kelly Marie:

    There's a policeman stood outside 24/7 and the buggers still get out to cause chaose




    ???

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