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Balanced 3 Phase Supply for EVC

Hi,

Please could someone advise on the following regarding EV chargers on a balanced 3 phase supply. 

We are proposing to install 3 x 75kw DC rapid chargers from a new DNO connection solely for the EV chargers. The chargers themselves only require 3 phase & earth and the only 230v supply from the new connection is a small anti-condensation heater within the feeder pillar (20w). 

Can I therefor still use the rule of thumb from CoP J4 as Regulation 722.411.4.1 (i) has now been removed from amendment 2? 

When I calculate using Regulation 722.411.4.1 (ii) I end up with a minus number so I assume this shows an earth electrode & PME supply is not suitable?

Thank you in advance.

Mark

  • Can I therefor still use the rule of thumb from CoP J4 as Regulation 722.411.4.1 (i) has now been removed from amendment 2? 

    Not if you want to comply with BS 7671:2018+A2:2022.

    When I calculate using Regulation 722.411.4.1 (ii) I end up with a minus number so I assume this shows an earth electrode & PME supply is not suitable?

    See Note 1 to A722.3 - you may be able to use 200 ohms as the answer if you have calculated the load imbalance neutral current correctly and it meets the criterial in Note 1.

  • sounds like there is no neutral current from the ev at all, and if a 400volt frost heater had been specified it would have been omitted totally.

  • sounds like there is no neutral current from the ev at all, and if a 400volt frost heater had been specified it would have been omitted totally.

    Im is the neutral current of the installation, not the single piece of EV charging equipment (see Part 2, symbols, p46 in BS 7671:2018+A2:2022)

    BS 7671 A722 recommends the worst-case imbalance possible in the installation is considered - see Note to A722.1

  • As the whole installation from the DNO cut-out consist of only 3 x 75kw DC chargers & 1 x frost heater, if we were to specify a 400v heater, could we therefor assume the installation to be balanced?

    The reason I ask is could we therefor remove the need for an O-Pen device on the PME installation or the need to covert to TT as O-Pen devices over 100A are still not readily available?

  • When you say 400 V heater, is that connected between two lines, or all 3 lines?

    Also, are the DC chargers Mode 4 only, or are they combined Mode 3/Mode 4 (so that if someone turns up in a Mode 3 only vehicle, they can still charge)?

  • The chargers are all Mode 4 only. 

    I have just tried searching for a anti-frost heater rated at 400v but haven't found one so installing a 230v one would cause the imbalance, albeit under 1A.

  • Indeed, though here is a shiny new DNO connexion solely for the chargers isn't it?  - I presume that means that  the transformer is spoken for by the chargers, or at least a large chunk of it. This is not a small extra load on a big factory  installation.
    mike

  • Yes, it will be a new connection solely for the chargers.

  • I wonder if Mike was thinking that if it's from a dedicated transformer you might be able persuade the DNO to give you a non-PME supply (TN-S or PNB).

       - Andy.

  • So, even with 1 A of imbalance neutral current Im, I get 97 ohms from the formula in A722.3 for three-phase installation.

    BUT, this illustrates the importance of correctly estimating the neutral current.