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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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    lyledunn: 
     

    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?

    Selectivity (or lack of it) may mean that if there's an issue downstream of the "EV RCD", the upstream RCD will trip first. If the RCD operation is required to disconnect all live conductors, where there is no selectivity, surely all upstream RCDs should meet the requirement?

    Whilst I accept this point of view could be a link back to the “general rules” as Andy has pointed out, in the discussion in this thread, I believe there is a world of difference … purely because the words regarding “protection against DC residual fault currents” is wide open to broad interpretation. That is, no performance requirement as to the level or type of “DC residual fault currents” is stated regarding the criteria for permitting Type A or Type F upstream … whether that's the right approach or not, is yet another question.

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  • 0

    lyledunn: 
     

    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?

    Selectivity (or lack of it) may mean that if there's an issue downstream of the "EV RCD", the upstream RCD will trip first. If the RCD operation is required to disconnect all live conductors, where there is no selectivity, surely all upstream RCDs should meet the requirement?

    Whilst I accept this point of view could be a link back to the “general rules” as Andy has pointed out, in the discussion in this thread, I believe there is a world of difference … purely because the words regarding “protection against DC residual fault currents” is wide open to broad interpretation. That is, no performance requirement as to the level or type of “DC residual fault currents” is stated regarding the criteria for permitting Type A or Type F upstream … whether that's the right approach or not, is yet another question.

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