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Simultaenous Contact

Dom

Good afternoon all, 

I am seeking the collective views of the group regarding the issues we are currently encountering within the EV installation environment in relation to simultaneous contact.

In simple terms, we are seeing a significant number of installations where customers have lamp posts located within their driveways. In many of these cases, it is not possible to achieve the recommended 2.5‑metre separation distance.

My position is that, where physical separation cannot be achieved, the application of layered protection at the EV charge point and associated switchgear would leave the customer in no worse position than prior to the installation. It is accepted that the proposal only outlines protection on the vehicle, but there are no other solutions for industry, are we with the protection detailed taking enough measures to carry out an install and in affect leave the install without a subsantial increase in risk?

My proposed approach to managing simultaneous contact risk would follow a structured hierarchy as set out below:

  • Can the maximum separation distance be achieved?
  • Can barriers or enclosures be installed to prevent simultaneous contact?
  • If neither of the above options are achievable, can layered protection provide an acceptable level of risk mitigation?

With layered protection, the proposed measures would include:

  • Installation of a compliant open‑PEN (O‑PEN) protective device
  • Provision of a double‑pole 30 mA Type A RCBO
  • Use of a charge point - M3 21 mA protection

Based on the above, the assumption is that, if all protective measures are correctly installed and verified, the installation would incorporate:

  • Automatic disconnection within the required times
  • Residual current protection
  • Open‑PEN fault detection

This combination of protections would significantly reduce the likelihood of a fault condition persisting for any meaningful duration.

On this basis, the key question for consideration is:

Where physical separation and barriers are not achievable, would it be considered acceptable to proceed with installation relying on this layered protection approach?

Parents
  • 0
    Dom said:
    I also have issue with the 2.5 metre distance. I belive this may be taken from the placing out of reach measurement. The averge finger to finger span is around 1.75 metres - I think it would be good to get some clarity on this as well. 

    The clarity is provided in BS 7671 (and IEC/HD 60364 series, IEC 60364-4-41). It could not be more plain.

    Simultaneously accessible is explained quite clearly in Regulation Group 417.3, including Figure 417. The 2.5 m is clearly stated in terms of an interpretation of 'simultaneously accessible'

    The basic principle is in the NOTE to Regulation 417.3.2:

    We wouldn't ever use the 'average finger to finger span' but an arm span that a large percentage of the population is guaranteed to be under. The P95M (95th percentile male) value of arm span, means that 95 % of males will have an arm span less than the value, and that is 1.90 to 1.96 m ... hence, when calculations are carried out by DNOs for their earthing systems, which aligns with the approach for HV standard BS EN IEC 61936-1 and BS EN 50522, they will use a value of 2 m.

    However, the value in IEC/HD 60364-4-41 and BS 7671 is likely to be the P95M arm span, holding something conductive of length 250 mm ish in each hand, or holding something conductive of length up to 500 mm in one hand.

    Don't forget, HV standards for touch/step potential are usually mainly applied within the boundaries of substation fences (or similar) where only skilled, instructed or supervised persons, wearing appropriate clothing and footwear, are intended to be present. BS 7671 on the other hand has to be suitable for 'ordinary persons' for the most part.

  • 0 in reply to gkenyon

    Thanks Graham - I knew the note was present, the point I would challenge is the 2.5 metre. However you have clearly articulated where this figure comes from. I do feel there may be a case to look at this in terms of the additional 250mm-500mm hand held point however I also see the importance of the worst case sceanrio. What would be benficial is looking at the stats behind actual events and quantifying what we have seen over the years. Granted this does not elliminate the risk but like O-pen it provides detail into the level of occurence. 

  • 0 in reply to Dom
    Dom said:
    I do feel there may be a case to look at this in terms of the additional 250mm-500mm hand held point however I also see the importance of the worst case sceanrio.

    Since these are part of the fundamental requirements of BS 7671 and HD/IEC 60364-4-41, that will need to be proposed for work at international level, and agreed there, as well as in the UK.

    It is also worth noting that the principle of "arms' reach" and the values associated with it (1.25 m for 1 arm, 2.5 m for two arms or arm above head of someone standing), are not new either ... they were illustrated in Figure 1 of the 15th Edition of the IEE Wiring Regulations in 1981:

    The requirement in broadly its current form for simultaneously-accessible exposed-conductive-parts to be connected to the same earthing system where ADS is used has been in place since the 16th Edition of the IEE  Wiring Regulations was published in 1991 (Regulation 413-02-03).

    These things may be inconvenient for this discussion, but we need to be careful not to throw the baby out with the bathwater. They are key principles that have been in place for a substantial length of time - at least 35 years now.

Reply
  • 0 in reply to Dom
    Dom said:
    I do feel there may be a case to look at this in terms of the additional 250mm-500mm hand held point however I also see the importance of the worst case sceanrio.

    Since these are part of the fundamental requirements of BS 7671 and HD/IEC 60364-4-41, that will need to be proposed for work at international level, and agreed there, as well as in the UK.

    It is also worth noting that the principle of "arms' reach" and the values associated with it (1.25 m for 1 arm, 2.5 m for two arms or arm above head of someone standing), are not new either ... they were illustrated in Figure 1 of the 15th Edition of the IEE Wiring Regulations in 1981:

    The requirement in broadly its current form for simultaneously-accessible exposed-conductive-parts to be connected to the same earthing system where ADS is used has been in place since the 16th Edition of the IEE  Wiring Regulations was published in 1991 (Regulation 413-02-03).

    These things may be inconvenient for this discussion, but we need to be careful not to throw the baby out with the bathwater. They are key principles that have been in place for a substantial length of time - at least 35 years now.

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