One for the EV chaps

Discussion in 'Electricians' Talk' started by sparky Si-Fi, May 19, 2020.

  1. sparky Si-Fi

    sparky Si-Fi Screwfix Select

    Morning all

    Not up to speed with Tesla car charging, in the White Meter box, small three way CU for two EV charging points, with a spare way which I am hoping to use as a supply down to a garden studio.

    No room in the Meter box for a larger Cu (yes I know they arent supposed to be in there, but that aint changed in yonks)

    Now I cant find anything in 722 that says its a no goer, one thing I did notice is the supply is TN (via 30mA RCD and no sign of a rod so the point is basically a TT )is being used for the final circuit to the charging point (722.411.4.1)

    Now this I have always known as a no go using suppliers earth as loss of neutral and potential has a risk of making all your exposed metal work live, but thats common knowledge

    So the long and the short of it is , can the spare way be used to run a 6mill 3C SWA 32A supply to this Studio, Physics says, yaaas, Computer says?

    Cheers chaps,

  2. sparky Si-Fi

    sparky Si-Fi Screwfix Select

  3. Coloumb

    Coloumb Screwfix Select

    I'm not sure what it is your trying to do? The cu is already there and you want to run a sub main off it? Or it's not there and you want to add a cu with 2 x ev and a sub main? And this is PME?
  4. nigel willson

    nigel willson Screwfix Select

    Surely. PME ,cable sheath of armoured. Isolate and TT at other end ?!
  5. Active Member

    You really need to know what the supply is as well as the load on the existing install.

    Some chargers do not need any earth rod or TT as they have built in earth / neutral loss detection - I think the Wallbox Pulsar Plus has it built in.

    It has to be taken in to account that adding more load to the install will reduce the available Kwh to the car(s) being charged.
  6. sparky Si-Fi

    sparky Si-Fi Screwfix Select

    HI chaps

    OK thanks for replies,

    Supply PME, Three way CU in place, two ways used for EV car chargers, spare way left in place which I was going to use for a sub out to a cabin

    3C 6mm, 32A sub, in a duct, 22mts away

    Calcs all ok

    My question is/was sharing the same CU for a sub-cable which has been installed and intended for Car chargers, supply tails are 25mm with 100A sat in the carrier as the norm.

    As I am not up to speed with these vile eco-box vehicles, was there any issues in regs, none that I can see.

    So its my design to run it from this small spare way in the CU, disconnect the PME in the cabin and rod it down as the norm for outbuildings

  7. sparky Si-Fi

    sparky Si-Fi Screwfix Select

    How would this reduce the demand to the car charger, increase in load yes (not by much) there still going to pull whatever they need with or without the loading to the cabin ?
  8. Banallsheds

    Banallsheds New Member

    One day when the powers that be decide to tax electricity for cars you are going to find you cabin expensive to run.
  9. Active Member

    Car chargers are usually set by installers to prevent overloading the main fuse- for example if the load is estimated at 40A existing then a 100A supply may have 60A left
    When you look at a charger that can pull 40A on a single phase you may need to set the total load available to 60A between them- when the cat charges tom 80% the load drops off dramatically.

    Each charger can be set to a maximum output (they can also be paired to allow load sharing),if installing a significant extra load then it can be problematic

    Some chargers have a current transformer on the main incomer to prevent over load, the charger reduces for a period if a shower / cooker is turned on.

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