Well, things like bus-stops and traffic lights may have an un-metered connection, and be billed on calculated consumption. This is likely to be fused at 10A or less in the cut-out, and the incoming supply cable may well be less than 10mm2

The more common case for lights around a building is an outside light that us one of many final circuits within the building, perhaps on its own CU but in practice still part of a larger installation, with a main fuse and supply cable sized to match the 100A supply or whatever so 25 or 35mm2 incomer - with potential for proportionally higher diverted neutral currents.

Mike

Correct

I am doing buildings so this is exactly the case

The lighting columns are final circuits and to me really the metal columns is no different than a cooker's metal cover.

Looks to me more like an exposed conductive part.

So am i right to understand that this regulation does not really apply in this case?

Looks to me more like an exposed conductive part.

Other than it's stuck in the ground, so provides some path to true Earth for diverted neutral currents...

That said, it's likely to have a ground resistance of several tens of Ohms, so the current flow is likely to be very restricted - so not a huge worry for a single column (but maybe you wouldn't want to rely on the 0.75mm² c.p.c. in a flex to the lighting head).

Maybe less restricted if you had many columns (long drive to a country mansion) - where the overall resistance of many in parallel could be reduced a fair bit.

Steel column have been debatable in terms of exposed- or extraneous- for a long time. Are they part of the electrical installation, or just supporting/enclosing it? If you had unsheathed singles inside it should be an exposed-conductive-part and therefore cannot be an extraneous-conductive-part (perhaps counter-intuitively, but that's what the definitions say). If sheathed cables inside, but the column in contact with a class 1 lighting head, then extraneous-conductive-part would seem to fit.

   - Andy.

Quite - it is not always clear what the risk is for which we need the CPC .. to carry a diverted neutral current needs a big one, comparing to the DNOC cable, while to blow a fuse doesn't need anything larger than the final circuit  supply rating,  and to trip an RCD probably does not need a CPC at all if the thing is planted in the ground.

The regs do not really make the distinction.

mike

Apostolos said:

If I have lighting columns at the back of a building and I am feeding them from inside the building, and the building system is a PME system, does this apply?

If you are after the consumer's meter in a building, this does not apply. As others have said, this is for unmetered supplies, such as those used for feeding street lighting direct from a distribution main in the street. The arrangement would be familiar to anyone who has done street/highway works, perhaps not so if you've only worked in buildings and on private land (perhaps give or take old MOD/government premises).

In some respects making the light head Class II (so no connection between c.p.c. and column) and ensuring that everything internal is sheathed or in insulating enclosures has something to be said for it.

   - Andy.

Although given the recent changes to 411.3.1.2 (main bonding now only required within buildings) - 714.411.203 & 714.411.3.1.2 might be due a bit of a re-think...

   - Andy.

AJJewsbury said:

Although given the recent changes to 411.3.1.2 (main bonding now only required within buildings) - 714.411.203 & 714.411.3.1.2 might be due a bit of a re-think...

Not sure what you're getting at Andy? 714.411.203 says "any main protective bonding conductors" (doesn't say there has to be some, just any if you have them) ... Just because BS 7671 doesn't mandate main bonding doesn't mean someone hasn't decided to provide them, but if you do, the sizing requirements are there.

Similarly, 714.411.3.1.2 supports the concept "need not be ..." - it all lines up, and provides clarity to an often-asked question?

or ... have you noted something else?

Similarly, 714.411.3.1.2 supports the concept "need not be

That was written in the days when 411 required bonding of extraneous-conductive-parts in general - so a 714 regulation was needed to "modify" the general requirements. Section 700 is all about supplementing or modifying general requirements. Now the general requirements no longer contradict, there's no need for such a regulation at all - its very presence suggests a difference from general requirements - which isn't the case. To my mind 714.411.3.1.2 should disappear (or keep some of the reassuring words as a NOTE as best).

714.411.203 says "any main protective bonding conductors" (doesn't say there has to be some, just any if you have them)

Agreed, although if there are no bonded extraneous-conductive-parts, why does the Earthing conductor have to be sized for PME?

Going off on a bit of a tangent, I still feel there's a bit of an elephant in the room with the change to 411 to only require bonding within buildings - as we've then lost the previous protection that c.p.c.s feeding Class 1 equipment that was in contact with extraneous-conductive-parts outdoors from being forced to carry potentially large diverted N currents (or other large currents, from faults or imported from outside the installation), that previously main bonding conductors would provided a low impedance by-pass for).

   - Andy.

I like the sound of Class 2 with double insulation of conductors