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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....





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    davezawadi:

    Graham

    It is easy to say that, but the car case is subject to a new(ish) standard, and some expect it to become common. I could treat it exactly like a caravan, but in reality it is probably more dangerous and TT is only a partial answer. The main difficulty is that cars are charged near PME earthed locations (garages, garden taps etc.), and at the same time the PME system is broken due to poor maintenance. Our answer is to make a fairly unsatisfactory set of regulations (I think most qualified people agree), and worry about the problems on a forum. Yes, the UK should permit only class 2 cars for new sales! The owners of the present vehicles would have the same problem that diesel drivers have, they changed the rules. They were changed to make the country safer, why not? CUs were changed to metal for "safety", why not cars?




    If you have a proposal to either standards committee, I'm sure they'd be grateful to receive it.


    The PME system is NOT simply "broken due to poor maintenance"- it's a casualty in the changing face of the "fortuitous earthing system" that was the network of metal service pipes and certain distribution cable types.


    I'm not sure what "regulations" are unsatisfactory - I know of no specific legislation which covers this?


    I understand the "class II only" argument, but I'm not in a position to answer whether that's possible for specific reasons (e.g. plug-in hybrids, whether a protective conductor connection is preferred for static control etc.). Certainly, it is well outside the scope of BS 7671, because it's simply something someone will plug into an installation, it's not part of the "selection and erection" process?

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  • 0

    davezawadi:

    Graham

    It is easy to say that, but the car case is subject to a new(ish) standard, and some expect it to become common. I could treat it exactly like a caravan, but in reality it is probably more dangerous and TT is only a partial answer. The main difficulty is that cars are charged near PME earthed locations (garages, garden taps etc.), and at the same time the PME system is broken due to poor maintenance. Our answer is to make a fairly unsatisfactory set of regulations (I think most qualified people agree), and worry about the problems on a forum. Yes, the UK should permit only class 2 cars for new sales! The owners of the present vehicles would have the same problem that diesel drivers have, they changed the rules. They were changed to make the country safer, why not? CUs were changed to metal for "safety", why not cars?




    If you have a proposal to either standards committee, I'm sure they'd be grateful to receive it.


    The PME system is NOT simply "broken due to poor maintenance"- it's a casualty in the changing face of the "fortuitous earthing system" that was the network of metal service pipes and certain distribution cable types.


    I'm not sure what "regulations" are unsatisfactory - I know of no specific legislation which covers this?


    I understand the "class II only" argument, but I'm not in a position to answer whether that's possible for specific reasons (e.g. plug-in hybrids, whether a protective conductor connection is preferred for static control etc.). Certainly, it is well outside the scope of BS 7671, because it's simply something someone will plug into an installation, it's not part of the "selection and erection" process?

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