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Delivery Robots & Section 722 of BS 7671

Daniel Hickson

Hello all, 

My question is providing a compliant power supply to electric delivery robots that deliver food items from a Food Store. 

The power supply will be sourced from the stores electrical supply and an armoured cable installed below ground or clipped direct dependant on site specifics which then serves the delivery robots power supply unit. This PSU serves the charging hub which then provides a charging facility through induction. 

The supply is SP&N and has a maximum load of circa 10A. The equipment is classed as class 1 equipment that requires an earth connection. The PSU contains only a MCB as a protective device. The majority of the stores serving the delivery robots will be a TNC-S PME supply.

Regulation 722.411.4.1 is descriptive that a PME earthing facility is not permitted to be utilised to serve an outdoor charging point, unless suitable mitigation methods are introduced.

For EV charging, this is often achieved through the provision of O-PEN protection either within the EV chargers manufactures equipment or within the DB.  

To me, even though the risks are smaller than an EV charger and the Wiring Regulations are only descriptive for an and Electric Vehicle, they are still apparent if there is a loss of a PEN conductor within the network resulting in possible live metallic parts.

Would anyone be able to input on this to assess if this approach may be over engineered.

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  • +1

    I'm not sure 722 is in scope for your application - the PME precaution is based on the assumption that the body of the vehicle (being likely to be touched by by a driver or passengers) can be made hazardous live by a broken PEN event. Since you have only inductive connection to the "vehicle"  722.1 (i) would put it out of scope I think.

    Generally Class 1 equipment outdoors connected to a PME system can pose some risks, which you might consider mitigating, but that's above and beyond BS 7671 minimum requirements.

        - Andy.

  • 0 in reply to AJJewsbury

    Hi Andy, thanks for this. The robots are plastic, however, the PSU and charging hub are exposed ground mounted equipment. So I was highlighting a potential risk with the charging hub. 

  • 0 in reply to Daniel Hickson
    Daniel Hickson said:
    The robots are plastic, however, the PSU and charging hub are exposed ground mounted equipment.

    It's not the EVSE (charging equipment) that BS 7671 requires protection for in 722.411.4.1, but the charging point, i.e. the connection to the vehicle ... in other words, the vehicle (like a caravan, or mobile and transportable unit), if it is charged outdoors, can only be connected to a PME earthing arrangement if certain conditions are met.

  • 0 in reply to gkenyon

    It may be worth comparing the risks to other outdoor class 1 things, there are plenty of bus stop signs and lamp posts powered from TNC-s /PME supplies without too many dead bodies found around them in the morning. 

    You do not have to have a perfect system, just one that is justifiably safe. If anything an automated system is probably safer than a normal plug in car charger, as there won't be anyone there to get a shock anyway.

    The inductive part removes the thing that is most dangerous for an EV, namely the connection from the mains CPC to a large body of exposed metal that you can be sure someone will touch, leaving you only with the charger itself - which I suspect is no more or less dangerous than any other outdoor electrical item.

    Mike

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  • 0 in reply to gkenyon

    It may be worth comparing the risks to other outdoor class 1 things, there are plenty of bus stop signs and lamp posts powered from TNC-s /PME supplies without too many dead bodies found around them in the morning. 

    You do not have to have a perfect system, just one that is justifiably safe. If anything an automated system is probably safer than a normal plug in car charger, as there won't be anyone there to get a shock anyway.

    The inductive part removes the thing that is most dangerous for an EV, namely the connection from the mains CPC to a large body of exposed metal that you can be sure someone will touch, leaving you only with the charger itself - which I suspect is no more or less dangerous than any other outdoor electrical item.

    Mike

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