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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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    gkenyon: 


    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.

    Graham, can I ask where the requirement for all live conductors of the upstream RCD to be disconnected comes from if the RCD in the EVSE does that?

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    gkenyon: 


    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.

    Graham, can I ask where the requirement for all live conductors of the upstream RCD to be disconnected comes from if the RCD in the EVSE does that?

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