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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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  • 0

    AJJewsbury:




    is not very tough so I wouldn't use it underground as per the You Tube video ZoomUp posted.



    Actually SWA isn't that touch either -  it's easily pierced even by a simple garden fork never mind any kind of mechanical excavator - it's read advantage underground is from a surrounding c.p.c. that'll activate ADS rather than its physical toughness. In some ways, a copper rather than steel 'armour' might work better - which is actually what most modern buried DNO cables have.

     

    Tyre Company workshops wired in a black version of YY cable. Not so much innovation as cutting corners I think, as they basically wired the place in flex.



    I suspect it's more a cause of someone using continental contractors and them just doing what they usually do - German factories are routinely wired in YY etc (submains and all) - all according to their standards (which are normally held in reasonable regard). It begs the question: what's wrong with using "flex" for fixed wiring. We used to have a reg that prohibited it - but that dated from the day when "flexible cord" was a flimsy unsheathed composition of fine wires, cotton and rubber and nothing like as tough as the fixed wiring cables of the day - but these days when flex is plastic insulated and sheathed and so almost identical to many types of fixed wiring cable, other than the conductors are stranded. The reg has long since been deleted, but the memory of it seems to persist in folk memory for some reason. If anything using flex is normally more expensive (because of the extra work drawing many more strands and then twisting them together) - so it's hardly as cost cutting measure. It can however be quicker and easier to install and often makes better & more reliable connections in some common terminal types (or can be ferruled for screw tunnel terminals). So I'd make the case for considering it.


       - Andy.

     




    Hi Andy,Re: Continental contractors-

    No the guilty party was a local company although they may have foreign workers.


    I ahem heard the argument before that you could -in theory- wire a house in flex, but would you do it?  The testing bodies frown upon using any flexible style cables until they are to BASEC standards, and although many may be in the pipeline until a cable is certified it shouldn't be used at least in a final circuit, at present they are listed as: "These cables have a wide variety of uses in construction and for powering appliances and equipment."  ( Basec) link - https://www.basec.org.uk/cables/.

    But they are not listed as distribution or final circuit cables (yet).


    I'm not sure about your comments that you can pierce a steel armoured cable as easily as a flexible SY etc. The outer seating of an armoured is much tougher, and then there is the steel armour itself and then the inner insulation and then the cable insulation. A pretty good cable by any standards. The SY has a thin over-plastic sheath, then the stranded braid, then the grey plastic, no match in my book.

    I'm not saying I wouldn't install YY and SY, we do for cabinet and motor tails, but not as a final circuit until it is allowed to be included on an EIC ( by IET, NIC or ECA approval I mean). At the moment it would be a non-compliance.


    As for connecting up and terminating circuits, a lot of the push fit connections that are now employed by manufacturers for terminations ( LED down lights etc) are made for solid conductors.

    Loose strands leaking from  terminations of flexible cables are not uncommon when I inspect installations.

    Would using flexible cables encourage, indirectly, unskilled electrical works?

    I know that PVC/PVC is available at DIY sheds, but using 'flex' is a further step down the line to legitimising non-skilled installations.


    Regards



    Simon

Reply
  • 0

    AJJewsbury:




    is not very tough so I wouldn't use it underground as per the You Tube video ZoomUp posted.



    Actually SWA isn't that touch either -  it's easily pierced even by a simple garden fork never mind any kind of mechanical excavator - it's read advantage underground is from a surrounding c.p.c. that'll activate ADS rather than its physical toughness. In some ways, a copper rather than steel 'armour' might work better - which is actually what most modern buried DNO cables have.

     

    Tyre Company workshops wired in a black version of YY cable. Not so much innovation as cutting corners I think, as they basically wired the place in flex.



    I suspect it's more a cause of someone using continental contractors and them just doing what they usually do - German factories are routinely wired in YY etc (submains and all) - all according to their standards (which are normally held in reasonable regard). It begs the question: what's wrong with using "flex" for fixed wiring. We used to have a reg that prohibited it - but that dated from the day when "flexible cord" was a flimsy unsheathed composition of fine wires, cotton and rubber and nothing like as tough as the fixed wiring cables of the day - but these days when flex is plastic insulated and sheathed and so almost identical to many types of fixed wiring cable, other than the conductors are stranded. The reg has long since been deleted, but the memory of it seems to persist in folk memory for some reason. If anything using flex is normally more expensive (because of the extra work drawing many more strands and then twisting them together) - so it's hardly as cost cutting measure. It can however be quicker and easier to install and often makes better & more reliable connections in some common terminal types (or can be ferruled for screw tunnel terminals). So I'd make the case for considering it.


       - Andy.

     




    Hi Andy,Re: Continental contractors-

    No the guilty party was a local company although they may have foreign workers.


    I ahem heard the argument before that you could -in theory- wire a house in flex, but would you do it?  The testing bodies frown upon using any flexible style cables until they are to BASEC standards, and although many may be in the pipeline until a cable is certified it shouldn't be used at least in a final circuit, at present they are listed as: "These cables have a wide variety of uses in construction and for powering appliances and equipment."  ( Basec) link - https://www.basec.org.uk/cables/.

    But they are not listed as distribution or final circuit cables (yet).


    I'm not sure about your comments that you can pierce a steel armoured cable as easily as a flexible SY etc. The outer seating of an armoured is much tougher, and then there is the steel armour itself and then the inner insulation and then the cable insulation. A pretty good cable by any standards. The SY has a thin over-plastic sheath, then the stranded braid, then the grey plastic, no match in my book.

    I'm not saying I wouldn't install YY and SY, we do for cabinet and motor tails, but not as a final circuit until it is allowed to be included on an EIC ( by IET, NIC or ECA approval I mean). At the moment it would be a non-compliance.


    As for connecting up and terminating circuits, a lot of the push fit connections that are now employed by manufacturers for terminations ( LED down lights etc) are made for solid conductors.

    Loose strands leaking from  terminations of flexible cables are not uncommon when I inspect installations.

    Would using flexible cables encourage, indirectly, unskilled electrical works?

    I know that PVC/PVC is available at DIY sheds, but using 'flex' is a further step down the line to legitimising non-skilled installations.


    Regards



    Simon

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