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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
    Thanks Andy for the reply.


    Re: Earthing and double insulated:

    I have been trying to find different charging options for different cars. The Porsche charger ( not mine!) I installed ( early 2017), was a plug in unit which came with the vehicle and plugged straight into the mains, but we did it through an RCD and isolator, circuit, breaker, IP rated etc,.

    Admittedly it was a type A RCD, and not the DC sensitive Type B which is quoted in the 18th. I'm confident that the Porsche lead was two wire heavy duty cable ( no earth?), but I could be wrong.

    But your point that manufacturers have an intelligent charger that senses the earth is important, do they send a current down the earth and monitor it back, and is this the reason for the Type B RCD's, as they give back a small DC monitoring fault ?


    I wouldn't fancy being a cable jointer and finding during street mains connection alterations that several houses have EV's, and have just plugged them into wall sockets. The sum of the accumulation of potential  DC currents ( individually under 6 mA so the RCD Type B won't trip) in the PEN, when terminating, could be a major hazard. 


    I take your point about earthing and using the electrode or converting to TNS, but then you are back to using ADS with the Type B RCD, and all the load being put onto one phase often L1.

    Compliance with BS7671is a must, as you state, so losing the double insulated Electrical Separation cannot happen, but I am wondering why 722.413 has been left in ( Electrical separation). Perhaps just to allow future innovation or a separate rod just for the socket connection. The transformer and housing are yet to be priced but I would think they will be cheaper than the ( insert manufacturer) cost quoted at £ 375.00 for a wall pod with Type B RCD, plus the electrode.


    Many thanks for your comments.

    Simon 


Reply
  • 0
    Thanks Andy for the reply.


    Re: Earthing and double insulated:

    I have been trying to find different charging options for different cars. The Porsche charger ( not mine!) I installed ( early 2017), was a plug in unit which came with the vehicle and plugged straight into the mains, but we did it through an RCD and isolator, circuit, breaker, IP rated etc,.

    Admittedly it was a type A RCD, and not the DC sensitive Type B which is quoted in the 18th. I'm confident that the Porsche lead was two wire heavy duty cable ( no earth?), but I could be wrong.

    But your point that manufacturers have an intelligent charger that senses the earth is important, do they send a current down the earth and monitor it back, and is this the reason for the Type B RCD's, as they give back a small DC monitoring fault ?


    I wouldn't fancy being a cable jointer and finding during street mains connection alterations that several houses have EV's, and have just plugged them into wall sockets. The sum of the accumulation of potential  DC currents ( individually under 6 mA so the RCD Type B won't trip) in the PEN, when terminating, could be a major hazard. 


    I take your point about earthing and using the electrode or converting to TNS, but then you are back to using ADS with the Type B RCD, and all the load being put onto one phase often L1.

    Compliance with BS7671is a must, as you state, so losing the double insulated Electrical Separation cannot happen, but I am wondering why 722.413 has been left in ( Electrical separation). Perhaps just to allow future innovation or a separate rod just for the socket connection. The transformer and housing are yet to be priced but I would think they will be cheaper than the ( insert manufacturer) cost quoted at £ 375.00 for a wall pod with Type B RCD, plus the electrode.


    Many thanks for your comments.

    Simon 


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