Simultaenous Contact

My view is that the hierarchy you have outlined is sensible and follows a reasonable risk-based approach.

Where the recommended 2.5 m separation distance cannot be achieved, the first consideration should always be whether the risk can be eliminated through relocation, increased separation, or the installation of suitable barriers to prevent simultaneous contact. If these options are not reasonably practicable, then layered protection appears to be the next most appropriate measure.

Provided the installation includes a compliant O-PEN device, a double-pole 30 mA Type A RCBO, and the charge point’s integrated 6 mA DC protection (or equivalent), the risk of electric shock is significantly reduced through multiple protective measures operating together. In these circumstances, I would agree that the installation is unlikely to place the customer in a substantially worse position than existed prior to the EV charger installation.

That said, each installation should still be assessed individually, with the rationale for proceeding clearly documented within the risk assessment and design records. Particular consideration should be given to the accessibility of conductive parts, the condition and ownership of the lamp post, and any site-specific factors that could increase the likelihood of simultaneous contact.

Based on the information provided, I believe the proposed hierarchy and layered protection approach represents a pragmatic solution where physical separation cannot be achieved.

Certainly 230v is  entirely possible - it was one of the early arguments for not using PME supplies to things like bus shelters and lamp posts. although for a long time now, this has become the accepted  thing. Phone boxes (remember the old red ones) were always wired as double insulated in cases where they had a mains supply for lights or anything, as the old GPO standards were written by folk very nervous of introducing stray currents onto the phone network, and earth problems were considered a probable risk.

Arguably in the UK, a PEN fault can only occur on the network outside the customers control, as the NE bond is not on the consumers side of meters
mike

mapj1 said:

Certainly 230v is  entirely possible

Actually more than that ... possibly up to over 350 V ... if you take into account that the loads on the phases are not unity power factor. The chances of real-world conditions that might create such an unbalance are quite slim ... but possible nonetheless.

Would a 30mA RCBO in the lamp post for a UK residential street be a good idea maybe or would/should it also have some kind of OPEN fault device.  RCBO being quite cheap and not much more expensive than an MCB.  On a motorway I could see that the RCBO might not be a requirement and in fact it could be argued less safe if the lights went off.  

Sergio Fernandez said:

Would a 30mA RCBO in the lamp post for a UK residential street be a good idea maybe or would/should it also have some kind of OPEN fault device.

An a conventional RCD wouldn't provide any protection from hazardous voltages due to a broken PEN - as it's wired to L & N downstream of the N-PE link and the problem appears on the PE and so it'll neither detected the problem nor disconnect PE it even if the RCD does trip.

There are unconventional ways of using an RCD to see and disconnect on open-PEN faults (generally needing a local electrode that's outside of the influence of the PEN) - but in effect that's just re-inventing an open-PEN devices - you'd probably be better using a proper open-PEN device instead.

As you suggest, disconnecting the supply to street lighting isn't without its risks either - obviously increased risks to road users from collisions (especially those road users not expected to carry lights - e.g. pedestrians) and often a more general risk from other dangers that can more easily lurk in the dark (from thieves to worse). So often the choice to to pick the least worst risk overall.

The chances of a broken PEN are still relatively small - figures from a while ago IIRC put it very roughly at once chance in a million for any given installation - or to put it another way, it happens on average something like once per day across the UK - almost all of which end up causing no actual loss of life at all. Supplies dedicated to lamp-posts are reasonably safe as they have a low demand and have for a long time have been equipped with an additional electrode with is normally quite capable of keeping touch voltages down to safe levels.

Probably the simplest option is to make lamp posts Class II (and EVs too come to that).

   - Andy.

Morning Andy,

In my arena of work on fuel filling stations, and given small plot size and where EVSE been installed. And I appreciate its on the Duty Holders land, then traditional metal lighting columns been replaced with composite ones where the separation distance between the EV being charged and the existing column cant be increased.

Where there is possible issues with local authority lighting columns or other street furniture, of course we cant dictate for those parties to do something, then we simply install either a screen, fence panel or some sort of other suitable item that would protect from simultaneous contact.

Obviously as the designer, we do our best to keep those things separated, but this scenario should be picked up on scoping visit/feasibility study and the survey as recommended in the appropriate COP's for EVSE. 

I totally sympathise with the original enquirer on this post, but domestic installs will have far more of these situations than retail, commercial plots of land and installations.

Regards GTB 

I agree LA lighting columns will be out of the control of individual installers - but they're not entirely out of the control of the IET (or rather JPEL/64). Columns will be installed according to BS 7671 section 714 so a simple change to recommend the use of Class II in situations where the column would be within reach of other property might go a long way to mitigate the problem in the longer term. It might not even mean a move away from steel columns - I gather the internal wiring is normally sheathed these days, and connections enclosed so it might be as simple as swapping the lighting "head" to a class II version and removing the bond to the column. Class II equipment with a conductive outer case is hardly unknown.  It would need proper consideration though - perhaps the higher risk of impact damage means the ordinary double/reinforced insulation approach might not be considered adequate - but even then there might be possibilities short of relying on the column for earthing - maybe using screened cables (e.g. BS 8436) and earthed metal-clad equipment held away from the column would do.

    - Andy. 

I agree if BS7671 and the relevant product stanards make them Class 2 for residential streets and for private car parks like the Harvester etc (Other brands are also available).  I would still like to see an RCBO in the lamp post rather than an MCB.   On the railways it may need to differ as some use large DC and soforth

Unless you wish to protect people who have opened up the street lamp to steal power, the RCBO won't really save many lives in a single fault state, such as either an open CPC to the lamp post body or insulation failure. I agree if both occur together it would guard against the lamp post body becoming an accessible live part, which does occasionally happen.

https://www.bbc.co.uk/news/articles/clyz0kper56o

I'm not sure if the aggro of testing the things every 6 months, and probably resetting a fair few after each thunderstorm, is outweighed by  that. Maybe most use for lamps in accessible places that may be prone to damage or tampering.

Mike.

Thank you for your detailed response. I understand and appreciate the concerns you have raised regarding simultaneous contact risk and the limitations of relying on the OPDD in this scenario.

My earlier comments were based on the specific circumstances described, where multiple protective measures are present, including the OPDD, a 30 mA Type A RCBO, and the charge point’s DC fault protection. My intention was not to suggest that the OPDD alone provides protection against simultaneous contact risk, nor that it should be relied upon outside the scope of its product standard.

I agree that BS 7671 does not generally permit simultaneously accessible exposed-conductive-parts connected to different earthing systems, and that any departure would need to demonstrate that the resulting level of safety is not less than that achieved by full compliance.

My view was that, where physical separation cannot reasonably be achieved, a layered protection approach may help reduce risk. However, I acknowledge your point that risk reduction alone does not necessarily satisfy the requirements for a departure if the fundamental BS 7671 principles concerning earthing arrangements and simultaneous accessibility are not met.

Your observations regarding the assumptions within EV charging product standards and their interaction with BS 7671 are also noted and are an important consideration when assessing compliance and overall safety.

• Thank you for taking the time to set out your reasoning.

Terry osifo said:

My earlier comments were based on the specific circumstances described, where multiple protective measures are present, including the OPDD, a 30 mA Type A RCBO, and the charge point’s DC fault protection. My intention was not to suggest that the OPDD alone provides protection against simultaneous contact risk, nor that it should be relied upon outside the scope of its product standard.

To be 100 % clear on my view in this regard, the 'multiple protective measures' listed here are all required by BS 7671 as it stands, in addition to (and separately, and jointly, dependent on) the condition in Regulation 411.3.1.1 that simultaneously accessible exposed-conductive-parts are connected to the same earthing system.

I therefore can't see at all, how provisions of BS 7671, that rely on Regulation 411.3.1.1, can be used (separately and/or jointly) as a proposed 'mitigation' in the event that Regulation 411.3.1.1 is not met.

Terry osifo said:

My earlier comments were based on the specific circumstances described, where multiple protective measures are present, including the OPDD, a 30 mA Type A RCBO, and the charge point’s DC fault protection. My intention was not to suggest that the OPDD alone provides protection against simultaneous contact risk, nor that it should be relied upon outside the scope of its product standard.

To be 100 % clear on my view in this regard, the 'multiple protective measures' listed here are all required by BS 7671 as it stands, in addition to (and separately, and jointly, dependent on) the condition in Regulation 411.3.1.1 that simultaneously accessible exposed-conductive-parts are connected to the same earthing system.

I therefore can't see at all, how provisions of BS 7671, that rely on Regulation 411.3.1.1, can be used (separately and/or jointly) as a proposed 'mitigation' in the event that Regulation 411.3.1.1 is not met.

Thank you for the clarification. I agree that Regulation 411.3.1.1 is a fundamental requirement and that the protective measures specified elsewhere in BS 7671 are designed to operate on the assumption that simultaneously accessible exposed-conductive-parts are connected to the same earthing system.

My earlier comments were not intended to suggest that the RCBO, charge point DC fault protection, or OPDD could be used as alternative means of satisfying, or mitigating non-compliance with, Regulation 411.3.1.1. Rather, I was referring to the overall level of protection present in the specific installation described, assuming compliance with BS 7671 requirements.

Where Regulation 411.3.1.1 is not met, I agree that it would be difficult to rely on protective measures whose effectiveness is predicated on that condition being satisfied. The key question, in my view, is therefore whether the arrangement under discussion genuinely results in simultaneously accessible exposed-conductive-parts connected to different earthing systems, or whether the installation can be shown to comply with 411.3.1.1 by other means.

If the conclusion is that 411.3.1.1 is not satisfied, then I would agree that the discussion should focus first on addressing that non-compliance rather than on the additional protective measures provided by the equipment.