Streetside metal feeder pillar with PME supply

Open-PEN Detection Devices (OPDDs) are only recognized in BS 7671 for disconnecting the supply to an EV charging point, not other equipment.

Why has identified EPR of the feeder pillar itself as a particular risk, especially if it's installed according to BS 7671 considering the recommendations of ENA ER G12/5,  given that Regulation 114.1 of BS 7671 says:

For a supply given in accordance with the Electricity Safety, Quality and Continuity Regulations, it shall be deemed that the connection with Earth of the neutral of the supply is permanent. Outside England, Scotland, Wales and Northern Ireland, confirmation shall be sought from the distributor that the supply conforms to requirements corresponding to those of the Electricity Safety, Quality and Continuity Regulations (ESQCR), in this respect. Where the ESQCR does not apply, equipment for isolation and switching shall be selected accordingly as specified in Chapters 46 and 53.

Jeff Saunders said:

The bonding conductor from the MET to the feeder pillar is before the O-PEN device, so under PEN fault conditions the outgoing circuits will disconnect but the feeder pillar will rise in potential and will not disconnect from the supply.

This is no different to any other feeder pillar or item of street furniture, or other outdoor equipment or machinery.

The difference with an EV (vehicle itself) is, the vehicle is separated from Earth by rubber tyres, whereas the feeder pillar is generally ground-mounted in itself.

Jeff Saunders said:

Regulation 411.4.2 talks about the recommendation of installing an additional earth electrode on TN systems at the MET. Is this a feasible option to reduce the touch voltage on the feeder pillar under PEN fault conditions, if you could get a low enough resistance on the electrode?

This is not practicable, because of the required earth electrode resistances that you can achieve in most situations. The exception would be a large steel-framed and steel piled building, where that can be used as an electrode.

Jeff Saunders said:

Or are there any other options other than replacing, or installing a GRP feeder pillar in the first place? Or a front-end type O-PEN device?

As above, I would not necessarily recommend a front-end OPDD (and depending on the rating of the supply, it might not be practicable in many installations). A GRP enclosure would do the trick.

So would TT ... BUT only where a simultaneous contact assessment shows there are no issues with simultaneous contact of other street furniture, street lamps, etc., that are not connected to the same TT system.

(Note, the Simultaneous Contact Assessment should also be carried out even if you are using PME supply ... it should be verified with the DNO that their earthing arrangements connected to all simultaneously-accessible exposed-conductive-parts of equipment are connected to the same earthing system - see Regulation 411.3.1.1). 

Or are there any other options

Or, in short, don't worry about it! It's little different from many other examples of outdoor metalwork connected to PME - from domestic outside lights and heat pumps to lamp posts, gas pipes running from external meter boxes or many outside taps - and it's rare to see any broken PEN precautions to be seen for any of those.

   - Andy.

Thank you for your reply Graham, very helpful,

One issue we found though during an EICR of an existing 100A, 3 Phase, streetside EV installation was that in the process of the lamp columns being upgraded, they had also been relocated, so there is now a simultaneous contact risk between the lamp column and the feeder pillar rather than the protected EV side of the installation. 

I'm not sure who the responsibility or cost would now fall too now that it's been recognized, hence my question about an upfront type of OPDD as a solution if a company were willing to make one.

As you say, they are only recognized for EV charging points but wouldn't this be a relatively cost effective solution for existing installations and ones that arise in the future where the pavements are just getting more crowded with equipment?

Many thanks

Are the lamp posts and so on fed from different substations ? - unless they are the PME earth will  be common. A wander lead and a continuity check is probably all that is required to verify. Assuming all parts that might be touched would get live together, if PEN was lost, that is considered to be just fine.

Mike.

Jeff Saunders said:

One issue we found though during an EICR of an existing 100A, 3 Phase, streetside EV installation was that in the process of the lamp columns being upgraded, they had also been relocated, so there is now a simultaneous contact risk between the lamp column and the feeder pillar rather than the protected EV side of the installation. 

I'm not sure who the responsibility or cost would now fall too now that it's been recognized, hence my question about an upfront type of OPDD as a solution if a company were willing to make one.

An OPDD is not intended to be used to protect against simultaneous contact (Regulation 411.3.1.1), only earth potential rise (EPR) associated with open-PEN faults (Regulation 722.411.4.1).

EPR from PME, and the sorts of issues from "simultaneous contact" of different earthing systems, are two completely separate things.

Thanks to all of you for taking the time to reply to my questions, it is truly appreciated.

Thanks

Thanks Mike,

So as long as we get a reading in the region of 0.01/0.02 ohms between systems, we could reasonably assume that both were fed from the same substation? Is there any other way we could expect to get such a low reading?

Thanks

At that level, certainly fed from the same transformer or at the very least transformers whose earths are very solidly connected to a common earth *. Anything much less than an ohm is likely to be solidly connected. And most of the resistance in a  field test is probably probe contact via lightly oxidised metal.
The other way to think about an acceptable resistance  limit it is how many volts apart at credible current level. 

Mike

(* London mesh for example has some street mains with a transformers at each end.)

mapj1 said:

Anything much less than an ohm is likely to be solidly connected.

I'd perhaps not make the statement for all urban arrangements ... the "solid" connection might be via a gas main, which is definitely not ideal. Yes, it will manage the risk  ... at least until the main is replaced with plastic, which is the "but" or "however" part.

The best advice is check with the DNO.

It is unusual to bond modern all-electric lamp posts direct  to gas mains however, so the resistance will be higher if the path is via the nearest buildings on two substations that both share a common gas main.  
I agree the DNO should know, and the gas main replacement folk should be careful what they disconnect, but in reality both might have incomplete records, so to be sure, checking and asking are both a good idea.  As is remeasuring every few years as a matter of course, as things below ground  rot off un-noticed sometimes.

Mike.