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How much DC leakage is allowed on 100mA or 300mA type A RCD, impact on submains supplying EVCP's and other circuits on TT earths

Alan B

Just thinking about EV installs on TT earths where I have a 100mA or 300mA type A RCD protecting a submain, how much DC leakage can be applied before they are blocked.

There is a lot of discussion about EVCP not sharing a 30mA type A rcd with other circuits. But when that RCD/RCBO is then protected by an upstream 100mA or 300mA type A rcd along with other circuits, is it more tolerant to DC leakage current and by how much. Or should we be installing very expensive type B or type F RCD's.

Had a bit of a look around this and from what I case see the 100mA and 300mA devices can only tolerate 6mA DC leakage (Edited). This means that from my thinking at least a type A RCD can not be used to protect a submain or DB supplying an EV and any other circuit. I and I suspect many other electricians haven't been thinking about this.

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  • If the upstream RCDs are used to supply only charging points (and/or other loads) in which DC residual currents are unlikely, or if DC residual current protection is included in the charging points, then they also might be OK to be Type A or Type F

    Do we yet know if the d.c. components from EVs result from only faults, or could arise in normal service too? I'm thinking that if the EVSE incorporate 6mA RDC-DDs then we're protected from >6mA d.c. from that charge point - but if the submain is feeding say 3 charge points, and if the DC could arise from normal service, then the submain could be exposed to something just less than 3x 6mA and we're back to needing B-types again.

       - Andy.

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  • If the upstream RCDs are used to supply only charging points (and/or other loads) in which DC residual currents are unlikely, or if DC residual current protection is included in the charging points, then they also might be OK to be Type A or Type F

    Do we yet know if the d.c. components from EVs result from only faults, or could arise in normal service too? I'm thinking that if the EVSE incorporate 6mA RDC-DDs then we're protected from >6mA d.c. from that charge point - but if the submain is feeding say 3 charge points, and if the DC could arise from normal service, then the submain could be exposed to something just less than 3x 6mA and we're back to needing B-types again.

       - Andy.

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