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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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    Does Sect 714 apply to the light outside no.10? In my opinion yes. (714.1) It is a place open to the public, MPs are members of the public, and people and children visit.

    No.10 might also be considered a monument and is illuminated by the light, which is not fixed to the outside of the building (but, we assume, is supplied directly from the wiring of the building). Also if coppers play football there, it could be considered a sporting area.

    714.411.2.3.1.2 does not apply since the metalwork of the fence and the lighting enclosure are contiguous and form part of the outdoor lighting installation.

    If the supply is PME, and the "street electrical fixture" is class 1, then according to 714.411.203 the CPC should be 6mm minimum CSA.

    The glass lantern appears to be between 2.5 and 2.8M (1.6 x Theresa May), so as per 714.411.2.201 the door of the lantern requires a tool to open.

    If ADS is used as a protective measure, and the lantern is considered "street furniture",the door to the lantern "shall not be used as a barrier or enclosure".

    More to it than meets the eye.





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    Does Sect 714 apply to the light outside no.10? In my opinion yes. (714.1) It is a place open to the public, MPs are members of the public, and people and children visit.

    No.10 might also be considered a monument and is illuminated by the light, which is not fixed to the outside of the building (but, we assume, is supplied directly from the wiring of the building). Also if coppers play football there, it could be considered a sporting area.

    714.411.2.3.1.2 does not apply since the metalwork of the fence and the lighting enclosure are contiguous and form part of the outdoor lighting installation.

    If the supply is PME, and the "street electrical fixture" is class 1, then according to 714.411.203 the CPC should be 6mm minimum CSA.

    The glass lantern appears to be between 2.5 and 2.8M (1.6 x Theresa May), so as per 714.411.2.201 the door of the lantern requires a tool to open.

    If ADS is used as a protective measure, and the lantern is considered "street furniture",the door to the lantern "shall not be used as a barrier or enclosure".

    More to it than meets the eye.





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