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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....





  • 0

    Zoomup:

    Easy peasey, just use this method using the support pole as an earth electrode. You are all overthinking the matter. Run your three phase supply cable in a nice colourful buried plastic tube and all's well.

    https://www.youtube.com/watch?v=zSO9vrjmGZo


    Z.


     








    Zoomup- Er not sure of the Dutch method of installation. At least he had correct colours on the phases, CENELEC compliant? Still great music.


     

  • 0

    Zoomup:

    The IEEE has looked into this matter before.

    https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=8303690


    Z.




    Thanks Zoomup:


    Very interesting article from the IEEE. 


    WE seem to be heading down the RCD route though:


     I noted the Electrical Safety First comment:

    "If you are charging from a 13A mains socket in your home, ensure the wiring in your property has been checked prior to doing so. Old wiring may not be able to cope with the demand from charging your vehicle overnight and risk a fire in your property."  


    Most houses will have a Type A RCD if any, and these won't pick up the DC element that the NICEIC is staying as a must.  (ESF was once part of the NICEIC).  Shouldn't they just say get an electrician to install dedicated circuit?

    If we don't get the message clear from the outset we know people will just cut corners, this is the chance to get it right now.

    People need to view it in the same way Gas is viewed especially due to the direct/indirect contact and being 'outside the safety cage'.


    Thanks



    Simon

  • 0

    "If you are charging from a 13A mains socket in your home, ensure the wiring in your property has been checked prior to doing so. Old wiring may not be able to cope with the demand from charging your vehicle overnight and risk a fire in your property."  


    Most houses will have a Type A RCD if any, and these won't pick up the DC element that the NICEIC is staying as a must.  (ESF was once part of the NICEIC).  Shouldn't they just say get an electrician to install dedicated circuit?



    The main problem with using 13A sockets isn't so much the wiring as the sockets themselves - some brands have been found to be rather lacking when called on to carry the full 13A for many hours - they've been overheating ? (hence the new requirement for new "EV" marked sockets.)


    Where a 13A socket is used the EV connection lead will have to incorporate a box containing a protection system (like the contents of a wall pod) - some of these incorporate B-type RCD or other means of tripping if d.c. leakage exceeds 6mA - so protecting any upstream A-type (or AC-type) RCDs from being blinded - so in practice there might not be a too much of problem.


      - Andy.
  • 0
    Thanks Andy,


    What you say is true, most sparks/engineers have seen damaged sockets where kettles or heaters have been used at close to full load. The results are usually just damaged sockets but house fires kill as well as electrocution, and overloaded extension leads could lead to both.

    We are after all dealing with unskilled persons, and as Zoomup's newspaper articles show, accident are already happening.

    Surely it should be the case that "charging from a 13 A mains socket in your home" should be just outright stated as not possible/safe to the domestic consumer.


    I can just see the extension leads across the footpath of the rows of terraced houses now.....



    Thanks


    Simon.

  • 0

    SL1:

    Thanks Andy,


    What you say is true, most sparks/engineers have seen damaged sockets where kettles or heaters have been used at close to full load. The results are usually just damaged sockets but house fires kill as well as electrocution, and overloaded extension leads could lead to both.

    We are after all dealing with unskilled persons, and as Zoomup's newspaper articles show, accident are already happening.

    Surely it should be the case that "charging from a 13 A mains socket in your home" should be just outright stated as not possible/safe to the domestic consumer.


    I can just see the extension leads across the footpath of the rows of terraced houses now.....



    Thanks


    Simon.

     




     

    As EVs become more popular, there are going to be more occasions when people want to charge off a "granny lead" when visiting other people (that's where the nickname comes from).


    These leads usually limit the charging current to 10A, so the heating should not be excessive.  If we say that people shouldn't be plugging appliances into 13A sockets, where will it end?  No kettles, no lawnmowers?  The whole point of a 13A socket on an RCD protected ring circuit is that unskilled people can plug things into them.
  • 0

    Zoomup:

    Easy peasey, just use this method using the support pole as an earth electrode. You are all overthinking the matter. Run your three phase supply cable in a nice colourful buried plastic tube and all's well.

    https://www.youtube.com/watch?v=zSO9vrjmGZo


    Z.




    Interesting. It looks to me that the earthing of the post was simply earthing it as an exposed-conductive-part, rather than as a TT electrode - he seemed to be using  the supply cable armour/screen as the main earth. If all the protective devices (including RCD) are built into the pod and the supply isn't PME then it really shouldn't be that much more complicated than that.


    The underground cable looked interesting - termination looked a lot simpler than SWA (although I might have preferred G/Y sleeving rather than tape)- I wonder if it was this type: https://www.nexans.nl/eservice/Netherlands-en/navigate_340594/VO_YMvKas_Dca_0_6_1_kV.html#description which seems to be a sort of cross between SY and CY and appears ro be designed for direct burial.


       - Andy.

  • 0
    Hi Andy,


    You are correct about the earthing as an exposed-conductive-part rather than using the pole as a TT electrode.



    Had a look at the cable and your link to the cable spec site.


    If the cable is a derivative of a SY cable the IET on-site guide specifically says that we couldn't use this type of cable: " every item of equipment must comply with a British or Harmonised Standard"   and " SY, YY and CY cables are not made to British or Harmonised standards."


    We had lots of emails from the NIC a few years back when a few contractors seemed tore using a black YY instead of SWA.


    Although I did notice that the cable was Nexus who do supply in the UK and it has an XPLE sheath so it would be worth checking.


    Regards


    Simon







  • 0
    Ah, I just said the cable was interesting - I wasn't suggesting you used it to supply your charge point. I always found it a bit odd that in the UK we mostly only seem to have a choice between T&E (which falls well below most world standards) and SWA (which seems overkill for most circumstances) - so I'm always interested in how they do things elsewhere.

     

    If the cable is a derivative of a SY cable the IET on-site guide specifically says that we couldn't use this type of cable: " every item of equipment must comply with a British or Harmonised Standard"   and " SY, YY and CY cables are not made to British or Harmonised standards."



    Ah, that old Chestnut again. The regulation they're referring to (133.1.1) actually goes on to say "In the absence of such a standard, reference shall be made to the appropriate International (IEC) standard or the appropriate standard of another country." (my emphasis). I'll let you work out if what the OSG says is an absolute truth or just a (over) simplification suited for a short guide book whose purpose is to avoid anything complicated like calculations or extra reading.


      - Andy.
  • 0
    Some of us are quite happy to specify and use SY and similar in situations where we think it is the best technical solution. It  is important to realise that the braid is really best used as an EMC thing and not intended either as armour against attack by sharp objects nor are the fine strands good as a high current CPC. But for flexibility and shielding, ideal.

    Equally there are those of us who consider BS7671 to be a guide, and not the last word in wiring standards, though I suspect to many others that is tantamount to heresy.  However, I mainly work in a research environment, and as that is always pushing at non standard solutions, it probably colours my thinking somewhat.
  • 0

    mapj1:

    Some of us are quite happy to specify and use SY and similar in situations where we think it is the best technical solution. It  is important to realise that the braid is really best used as an EMC thing and not intended either as armour against attack by sharp objects nor are the fine strands good as a high current CPC. But for flexibility and shielding, ideal.

    Equally there are those of us who consider BS7671 to be a guide, and not the last word in wiring standards, though I suspect to many others that is tantamount to heresy.  However, I mainly work in a research environment, and as that is always pushing at non standard solutions, it probably colours my thinking somewhat.




    Hi Mapj1:


    Yes innovation is not always the friend of set standards and on-site guides, and other standards may be good but not recognised yet.


    We use SY for local connections ( to machines, internal wiring etc).


    Good for shielding ( EMC), not a CPC, but the armouring or braiding is not very tough so I wouldn't use it underground as per the You Tube video ZoomUp posted.


    But still a good flexible cable for some uses, but not perhaps mains or sub-mains cabling as was the case reported a few years ago when we saw a few 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.



    Regards



    Simon.







     

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