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RCD Types for EV Chargers on TT systems

Former Community Member
Former Community Member

On a TT install, where the supply for EV chargers comes from a feeder pillar. If the EV charger has a 30mA Type B RCD, is there a requirement for an upstream 300mA Type B RCD or can it be a different type? 
Can I specify 300mA RCDs as the main switch (is this type B?), and what would the solution be if I wanted a 250A incomer, would I then need an additional upstream type B RCD for each charger between the distribution board and the charging unit. This is a very expensive component if needed.
Siemens and an article from Voltimum have indicated that the upstream RCD needs to Type B and the code of practice shows a 300mA RCD upstream on a diagram but not which type. 
Looking for some guidance on this and an explanation if possible.

Thanks

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    Assuming we are talking about Mode 3 chargers, then upstream RCDs don't need to be Type B as a result of the charger in all cases … provided of course the electronics in the EVSE itself doesn't generate DC residual currents.

    The issue that requires DC residual fault current protection to be in place, is a fault between a live conductor and PE downstream of the charger (e.g. in the charging cable or car), because of the pilot currents returning via PE from the vehicle to the EVSE.

    If the EV charger is protected by a Type B RCD, or a Type A or F with an RDC-DD, any DC residual fault currents downstream of that protection will be disconnected by those devices, and therefore upstream RCDs not affected.

    One issue regarding RCD protection upstream of EV charging equipment, is the requirement for all live conductors to be disconnected, as there is often no guaranteed selectivity between cascaded RCDs, even of higher residual current rating - the only way to ensure selectivity is to use an S-Type time-delay upstream of a non-delay RCD.

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  • 0

    Assuming we are talking about Mode 3 chargers, then upstream RCDs don't need to be Type B as a result of the charger in all cases … provided of course the electronics in the EVSE itself doesn't generate DC residual currents.

    The issue that requires DC residual fault current protection to be in place, is a fault between a live conductor and PE downstream of the charger (e.g. in the charging cable or car), because of the pilot currents returning via PE from the vehicle to the EVSE.

    If the EV charger is protected by a Type B RCD, or a Type A or F with an RDC-DD, any DC residual fault currents downstream of that protection will be disconnected by those devices, and therefore upstream RCDs not affected.

    One issue regarding RCD protection upstream of EV charging equipment, is the requirement for all live conductors to be disconnected, as there is often no guaranteed selectivity between cascaded RCDs, even of higher residual current rating - the only way to ensure selectivity is to use an S-Type time-delay upstream of a non-delay RCD.

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