The Downing Street problem

Perhaps the lamps/railings are an anti-terrorism device? Genuine visitors are briefed to not touch the railings under any circumstances, leaving terrorists to get zapped?

In the days when the police officers outside No. 10 were dressed in serge tunics and trousers complete with a helmet and kept their 38 revolvers concealed in their pockets or in a holster under their tunics they would get very bored during the early hours of the morning. I have been reliably informed that they would play football in Downing Street and apparently on one occasion the Prime Minister of the day opened an upper window and asked them to keep the noise down during one game.

I remember 10 Downing St before the gates. I saw Jim Callaghan behind us watching the crowds watching No 10.

Is there a No. 1 Downing St? ?


The north side of the street looks like a row of Georgian houses, but in reality is one government building. It won't be wired like any ordinary row of terraced houses, and anybody who does know about it won't tell.

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.

what does that reg say

That's the point of this post really - the regs say quite a few things - not all would seem appropriate for a situation like this - and then there's 'usual interpretation' like the presumption that the main 'equipotential zone' only needs to exist inside a building so often we don't think of bonding metalwork outdoors - which the regulations don't (clearly) say.


I guessed that the first thought of many (at least those used to normal domestics) would be to earth the light as if it were any other class I device (so a c.p.c. of say 1mm² or even 0.75mm² if the final connection is done in flex) and not to worry about bonding anything 'cos it's all outdoors to outside of the equipotential zone anyway. You could probably find sufficient words in BS 7671 to justify such an approach.


My worry then would be that the c.p.c could be pressed into doing doing the job of a main bonding conductor - i.e. carrying significant currents perhaps for a long duration (especially if there's PME in the vicinity) - which perhaps suggests we should bond the railings after all. 714.411.203's allowance to allow 6mm² is actually for earthing and bonding conductors for PME systems, not c.p.c.s, and in effect allows a reduction in size from the normal sizes in table 54.8 - so isn't really a minimum for c.p.c.s. In this case where the railings might be the only extraneous-conductive-part shared by two installations - such a reduction doesn't seem obviously sensible, so perhaps we should bond with full size bonding conductors (as per table 54.8 if the installations are PME) after all.


   - Andy.

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.

Hi Andy, what does that reg say, I haven't any books with me, and are both properties PME?

Ah, I've just realized I mis-read your comment (I read it as 'what do the regs say') - sorry!  714.411.3.1.2  is the one that says, for outdoor lighting systems, you can omit bonding to things like fencing that are close to but not part of the lighting installation.

  - Andy.