Metal street furniture without an electrical supply: can it be omitted from a simultaneous-contact assessment?

Sam Kindred said:

Can metal signposts, post boxes and bollards embedded in the ground within 2.5 m of a charging vehicle be omitted from the simultaneous-contact assessment, assuming no electrical equipment or connection to another electrical earthing system, even where they may introduce true-Earth potential?

Quite simply, yes.

Reasoning (italicised terms using the definitions in BS 7671):

These might be extraneous-conductive-parts, but they have no exposed-conductive-parts.

The 'simultaneous contact' issue of Regulation 411.3.1.1 applies to simultaneously accessible exposed-conductive-parts rather than extraneous-conductive-parts.

Further, from BS 7671:2008 to present, there is no longer a need to provide 'main' protective equipotential bonding to extraneous-conductive-parts outside buildings (although an indoor car park is an example of being within a building). Having said that,  supplementary local protective bonding, if and where specified, would extend to them from simultaneously accessible exposed-conductive-parts even outside buildings

Thanks, Graham, really appreciate you clearing that up. This has been a bit of a thorn in my side for a while.

What happens for crash barriers and other galvanised metal items, and those with stainless steel bolts and the like. It does appear to be a can of worms.

The well painted postbox and and the plastic sheathed sign posts do fit the no exposed-conductive-parts" rule, along with coated cabinets etc. 

Probably needs that extra bit of careful on-site observation for the unexpected...

I suspect there's still scope for confusion for things like steel lighting columns - are they exposed- or extraneous-conductive-parts? Modern setups use sheathed cables and enclosed equipment internally so the column itself isn't required to carry fault current in the way an exposed-conductive-part would, yet it's solidly bolted to the lighting "head" - normally Class 1 - so would tend to be raised to elevated voltages during faults etc in a similar way to an exposed-conductive-part.  I think by traditional definitions the column itself would be classed as an extraneous-conductive-part, but I can see an argument that it's more like an extension of an exposed-conductive-part. (But the same could be said of many bonded extraneous-conductive-parts - outside taps for example.)

Are we drifting towards two different kinds of extraneous-conductive-parts? One that can import any kind of voltage (Earth or from faults from elsewhere) and another which can import only a local Earth potential (and therefore carries less risk where nearby exposed-conductive-parts have precautions (e.g. open-PEN devices) to limit their variation from true earth (but not from other imported potentials).

  - Andy.

Philip Oakley said:

The well painted postbox and and the plastic sheathed sign posts do fit the no exposed-conductive-parts" rule, along with coated cabinets etc. 

Until you insert a bolt or screw.

Philip Oakley said:

The well painted postbox and and the plastic sheathed sign posts do fit the no exposed-conductive-parts" rule, along with coated cabinets etc. 

or an extraneous-conductive-part?

  - Andy.

AJJewsbury said:

I suspect there's still scope for confusion for things like steel lighting columns - are they exposed- or extraneous-conductive-parts? Modern setups use sheathed cables and enclosed equipment internally so the column itself isn't required to carry fault current in the way an exposed-conductive-part would, yet it's solidly bolted to the lighting "head" - normally Class 1 - so would tend to be raised to elevated voltages during faults etc in a similar way to an exposed-conductive-part.  I think by traditional definitions the column itself would be classed as an extraneous-conductive-part, but I can see an argument that it's more like an extension of an exposed-conductive-part. (But the same could be said of many bonded extraneous-conductive-parts - outside taps for example.)

A lot of the ones I see have a protective conductor connected ... but I do take this point, is this really necessary in all cases?

I think while one can see corner cases, there has to be a healthy dose of pragmatism - what we used to call EEBADS (Earthed, Equipotential Bonding) works indoors, but often becomes impractical outdoors, and we don't really have control of who plants what into the ground later and what the surface conductivity of the ground is. It also gets complex when folk do things like retrospectively screw security cameras or door entry systems to existing fence posts. 
It's also an argument for designing with double insulated outdoor mains kit where possible and certainly anything hand held for  long periods,
There is a small but unmitigable risk (*) from things like lost PEN or earthing systems that rise to high voltages during a remote fault, but  I think we sort of live with it.

Mike.

* I'm aware of the things like the o-PEN, but its only really intended for cars, and suggesting things like fuses or breakers in CPC earth paths is a big no-no (though functional earths for RF systems often have components in the earth path.)

I think while one can see corner cases, there has to be a healthy dose of pragmatism - what we used to call EEBADS (Earthed, Equipotential Bonding) works indoors, but often becomes impractical outdoors, and we don't really have control of who plants what into the ground later and what the surface conductivity of the ground is. It also gets complex when folk do things like retrospectively screw security cameras or door entry systems to existing fence posts. 
It's also an argument for designing with double insulated outdoor mains kit where possible and certainly anything hand held for  long periods,
There is a small but unmitigable risk (*) from things like lost PEN or earthing systems that rise to high voltages during a remote fault, but  I think we sort of live with it.

Mike.

* I'm aware of the things like the o-PEN, but its only really intended for cars, and suggesting things like fuses or breakers in CPC earth paths is a big no-no (though functional earths for RF systems often have components in the earth path.)