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RCD Types for EV Chargers on TT systems

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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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    CameronElmtronics: 
     

    Thank you for the reply gkenyon. 

    I thought this was the case but I had been informed by Siemens and Deopke that both charger and upstream RCD had to be Type B.

    Thanks again for the guidance.

    That interpretation can't be true, otherwise BS 7671 would not permit a Type A or Type F RCD in cases where the EVSE has built-in protection against DC residual fault currents (effectively equivalent to an RDC-DD or Type B RCD internally). See Regulation 722.531.3.101.

    The only time a Type B would be required upstream of the EVSE, is where the electronics in the EVSE itself somehow generates conditions where DC residual fault currents are propagated upstream. In general, that should not happen.

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    CameronElmtronics: 
     

    Thank you for the reply gkenyon. 

    I thought this was the case but I had been informed by Siemens and Deopke that both charger and upstream RCD had to be Type B.

    Thanks again for the guidance.

    That interpretation can't be true, otherwise BS 7671 would not permit a Type A or Type F RCD in cases where the EVSE has built-in protection against DC residual fault currents (effectively equivalent to an RDC-DD or Type B RCD internally). See Regulation 722.531.3.101.

    The only time a Type B would be required upstream of the EVSE, is where the electronics in the EVSE itself somehow generates conditions where DC residual fault currents are propagated upstream. In general, that should not happen.

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