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EV Chargers with built in RCD and 537.2.2

Ian Cheek

I read 537.2.2, and wonder if this applies to our EV charge points which offer built in 30ma and 6ma DC RCD's. Im sure these RCD must be electronic in nature. 

Upstream is a traditional MCB, so the EV Charger could be isolated.

However looking at 411.3.2.1 it has the line "the protecticve device shall be suitable for isolation of at least the line conductor"

So as 411.3.2.1 uses the term isolation, and the RCD is a protective device, should the inbuilt RCD comply with 537.2.2?

I'll stop reading the regs and have a cup of T, Thank you for looking, and in advance of your advice.

  • 0

    411.3.2 is about ADS - so in a TN system the protective device is likely to be the MCB, with any RCDs providing only additional protection, rather than ADS.

       - Andy.

  • 0

    Isolation can be single pole in TN earthed installations, but not in TT earthed installations.

    Bearing that in mind, how can the EV charger be isolated for maintenance and repairs?

  • 0 in reply to AJJewsbury

    Thank you for your time in replying. I’m happy with the position of the RCD in the hierarchy of the installations regarding ADS, additional protection etc.

    More my questions is of the electronics. Electronic isolation can not be used, based on my experience with electronic isolation, in its off state, it is only off if it tries to pull current, you can often still measure the input voltage at the output when it is switch (driven) off.

    The device will have a let through current before its state is realised, although the let through current is very small.

  • 0

    Well, RCDs for EV charging equipment must disconnect all live conductors (722.531.3.1).

    In addition, the RCD must comply with at least one of the following standards (722.531.3.101):

    • BS EN 61008-1
    • BS EN 61009-1
    • BS EN 60947-2
    • BS EN 62423

    Devices to each of these standards may perform isolation function (see Table 537.4). "Electronic" RCDs must still comply with the standards, which includes constructional standards, and a requirement for a test facility, etc. - which means if the RCD doesn't have all these things, you need a physical RCD up-front.

    With respect to individual charging points, perhaps the best place to get the answer to the question is the manufacturer. I have seen charging equipment that does have physical RCDs to the above standards installed.

    Incidentally, the RCD may be "backed up" by an RDC-DD to BS IEC 62955 (see also 722.531.3.101) which is a whole other set of considerations.

  • 0

    More my questions is of the electronics. Electronic isolation can not be used, based on my experience with electronic isolation, in its off state, it is only off if it tries to pull current, you can often still measure the input voltage at the output when it is switch (driven) off.

    It could well be that the switching mechanism is still mechanical even if the detection system is electronic (not unlike most RCBOs these days). Most EV charge points have an in-built contactor (to switch the charging current and ensure the connectors are dead when not connected to a vehicle) - so the RCD element could well operate though that.

       - Andy.

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