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Cable size for EV Charger

  • 17-11-2024 06:02PM
    #1
    Registered Users, Registered Users 2 Posts: 1,006
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    Hi all,

    Have a dedicated 6mm2 swa cable from house consumer unit to detached garage. Cable run is 42m.

    Will 6mm2 be sufficient to run a 7.4kw home EV charger over that distance? There will be no other load on this 6mm cable.


    thanks



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Comments

  • Registered Users, Registered Users 2 Posts: 2,203 drury..
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    It'll carry the load alright

    Afaik the installation voltage drops are 3/5 the english setup now which would be 11.5

    About 10v drop on that swa and then add voltage drop on tails and the voltage drop from shed to car charging unit

    So I reckon that would be tight and you'd be speccing 10s for that job

    Could be wrong there on some of that . Usually be over-engineering those jobs and probably going with 10 for spare capacity and reduced volt drop



  • Registered Users, Registered Users 2 Posts: 8,927 10-10-20
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    It being a detached garage, I'd guess that at some point in the future that wiring/lighting of it would then be required and the 6sq would no longer be suitable.



  • Registered Users, Registered Users 2 Posts: 2,203 drury..
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    Overnite car charging and general loads (lights and sockets ) could possibly be interlocked in theory so you may not always need additional capacity in this situation ,. depending on when exactly you're charging

    He seems to be on-the -limit there with the 7.4kw loading and installation voltage drop

    In practice that may or may not be ok depending on factors such as supply voltage , manufacturers specs, supply voltage drop etc



  • Registered Users, Registered Users 2 Posts: 8,927 10-10-20
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    Yep, 10sq to a sub-board would be a better option.



  • Registered Users, Registered Users 2 Posts: 1,006 Peppa Cig
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    thanks guys.

    I actually have a separate 10sq feed to separate garage sub-board to power planned garage conversion (lights/sockets/immersion/cooker/washing etc).

    So the existing 6sq will only ever supply the EV charger.



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  • Registered Users, Registered Users 2 Posts: 8,927 10-10-20
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    Then ask the REC to validate and test the existing cable and if all is well they should be happy enough to proceed.



  • Registered Users, Registered Users 2 Posts: 2,203 drury..
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    He'll need a REC out for a site survey with all that work potentially happening

    REC make a decision on those cables too.

    Hard to call that from here

    Overnite car charging and a GD load can usually be potentially interlocked so supply capacity may not not be an issue

    Adding a 2nd accomodation though means potentially extra supply capacity and mains etc upgrading. Would all need to be conformd onsite



  • Registered Users, Registered Users 2 Posts: 2,203 drury..
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    I wouldn't be buying or fitting any cables there unless all is confirmed



  • Registered Users, Registered Users 2 Posts: 8,927 10-10-20
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  • Registered Users, Registered Users 2 Posts: 2,203 drury..
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    Well hopefully his REC has confirmed all this and supply suitability/upgrade etc.

    There seems to be an awful lot of lads just adding up kva/kw numbers and checking fuse /mcb sizes

    And that's their version of electrical planning and design

    Not saying it's happening on this thread but it's rampant here and hazardous



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  • Registered Users, Registered Users 2 Posts: 8,927 10-10-20
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    Yep. At the end of the day it's the REC's prerogative based upon their education and experience to agree to use the existing cable or not. 👍️



  • Registered Users, Registered Users 2 Posts: 1,006 Peppa Cig
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    Cables already in situ. Just checking suitability of existing 6sq option that’s already there original build.

    Will upgrade if necessary but by the sounds of it it may be ok.


    Thanks



  • Registered Users, Registered Users 2 Posts: 2,203 drury..
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    Np

    By my rough calc (if correct(you may be just ok on the car charger

    There is a few variables though, existing supply voltage that sort of thing



  • Registered Users, Registered Users 2 Posts: 13,341 Calahonda52
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    I suppose painters could suggest they need to skim the walls before they paint them.

    “I can’t pay my staff or mortgage with instagram likes”.



  • Registered Users, Registered Users 2 Posts: 2,203 drury..
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    What is your point

    You're unaware that supply voltage could be a consideration if VD was tight or even if it's not



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