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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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  • Alan B said:

    There is a lot of discussion about EVCP not sharing a 30mA type A rcd with other circuits.

    There is no discussion necessary here regards the 30 mA "sharing", it's not permitted by BS 7671 ... 722.531.3.101 says 'each charging point incorporating a socket-outlet or vehicle connector complying with the BS EN 62196 series shall be protected individually by an RCD of Type A, Type F or Type B and having a rated residual operating current not exceeding 30 mA."

    The requirement says it all.

    Alan B said:
    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.

    Upstream RCDs need to be installed with reference to the currents they are protecting against. 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.

    Alan B said:

    Had a bit of a look around this and from what I case see the 100mA and 300mA devices can only tolerate 30mA.

    Again, this information is included in BS 7671 - see Regulation 531.3.2.

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  • Alan B said:

    There is a lot of discussion about EVCP not sharing a 30mA type A rcd with other circuits.

    There is no discussion necessary here regards the 30 mA "sharing", it's not permitted by BS 7671 ... 722.531.3.101 says 'each charging point incorporating a socket-outlet or vehicle connector complying with the BS EN 62196 series shall be protected individually by an RCD of Type A, Type F or Type B and having a rated residual operating current not exceeding 30 mA."

    The requirement says it all.

    Alan B said:
    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.

    Upstream RCDs need to be installed with reference to the currents they are protecting against. 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.

    Alan B said:

    Had a bit of a look around this and from what I case see the 100mA and 300mA devices can only tolerate 30mA.

    Again, this information is included in BS 7671 - see Regulation 531.3.2.

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