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Double wound safety transformer for EV supply.

SL1
Hi everyone, I have only posted once before so thanks to anyone who replies!


I am following on from the earlier "70 volt PEN conductor not allowed to exceed post", and looking into supplying a client with an electric vehicle power supply from a three phase isolating transformer BS 7671 722.413 (1.2): " The circuit shall be supplied through a fixed isolating transformer.."


The general consensus seems to be that an external IP box with an RCD (Type B) and a tethered lead is the standard to follow, and this may be the only option with a 230 volt domestic supply, but why not use a 3 phase 400 volt step down or tapped, safety double wound isolation transformer in a standard 100 -200 ampere or above industrial units/sheds?

( Subject to load and diversity).


The answer often stated when I have asked sparks/engineers is that in-rush current are too high but a type D CB BS 60898 will 'let through' the in-rush ( the transformer manufacturer agrees), and will still give at 5 seconds- (final circuit exceeding 32 A) 0.44 ohm EL ( 10oC) , so is achievable in many situations local to Birmingham.


I was then going to run a fused cable out to an external isolated IP 65 box with a Type 2 socket to IP44 or above ( 722.55.101).


Isn't it better to engineer a solution to the upcoming electric charger deluge, rather than buying (insert well known manufacturer name here), and lots of single phase loads usually dumped onto L1?


I would be interested in any thoughts or problems you may consider....





Parents
  • 0

    gkenyon:




    SL1:




    gkenyon:




    The situation that does arise, however, is high inrush current of the rather sizeable transformers. Yes, this can be overcome, but of course costs are now increasing, and we're competing against "forget it, I'll just plug it in to a socket-outlet", which of course is far less practical, and far less safe, but doesn't have the price tag attached.



     




     



    Just a thought on this ... Regulation 722.411.4.1 provides other options for three-phase installations. However, I guess such an approach would not be precluded, provided the requisite RCDs are used as indicated in the IET Code of Practice and to meet the requirements of section 722 of BS 7671.


     




    Thanks for you comments.






    However, isn't it the case that if you follow Section 722.413.1.2,  and use a Safety double insulated transformer Section 413 Electrical separation is in use.

    Therefore would the additional RCD's be required and isn't the RCD built into the manufacturers lead sufficient anyway? Surely a risk assessment could easily acknowledge that the separation system used, along with the manufacturers vehicle building-in RCD with purpose built lead and Type of socket.


    The point of the exercise was to use the transformer  protective measure rather than have the RCD so adding in the RCD on top would then defeat the idea of needing the protective separation measure, and introduce the CEN PME 70 volt rms etc problems.

     Isn't it an either/ or situation offered by Section 722?



    Regards


    Simon




     




     

Reply
  • 0

    gkenyon:




    SL1:




    gkenyon:




    The situation that does arise, however, is high inrush current of the rather sizeable transformers. Yes, this can be overcome, but of course costs are now increasing, and we're competing against "forget it, I'll just plug it in to a socket-outlet", which of course is far less practical, and far less safe, but doesn't have the price tag attached.



     




     



    Just a thought on this ... Regulation 722.411.4.1 provides other options for three-phase installations. However, I guess such an approach would not be precluded, provided the requisite RCDs are used as indicated in the IET Code of Practice and to meet the requirements of section 722 of BS 7671.


     




    Thanks for you comments.






    However, isn't it the case that if you follow Section 722.413.1.2,  and use a Safety double insulated transformer Section 413 Electrical separation is in use.

    Therefore would the additional RCD's be required and isn't the RCD built into the manufacturers lead sufficient anyway? Surely a risk assessment could easily acknowledge that the separation system used, along with the manufacturers vehicle building-in RCD with purpose built lead and Type of socket.


    The point of the exercise was to use the transformer  protective measure rather than have the RCD so adding in the RCD on top would then defeat the idea of needing the protective separation measure, and introduce the CEN PME 70 volt rms etc problems.

     Isn't it an either/ or situation offered by Section 722?



    Regards


    Simon




     




     

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