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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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  • Glen,

    Sorry made a mistake on previous post.  Should have said the 300mA or 100mA devices can only tolerate 6mA DC, therefore if other circuits are included in the sub DB, presumably in most cases there is likely to be additional DC leakage from those circuits. Most common would be a garage with LED lights and possibly a granny charger plugged in to a socket (I am seeing this more often in multi ev households). 

  • in reply to Alan B

    In scenarios like these, it is wise to select Type B or Type F

  • in reply to Alan B

    The question now makes sense.

    This information, at least regarding smooth DC residual currents, is in 531.3.3.

    AMK said:
    In scenarios like these, it is wise to select Type B or Type F

    Perhaps not Type F, which can only cope with 10 mA smooth DC.

    But again, this is all in Notes in Regulation 531.3.3.

  • in reply to gkenyon

    Certain manufacturers offer these devices at around £150 for a Type B RCD rated at 300 mA. That’s 5 x more than the type A equivalent.

  • in reply to AMK
    AMK said:
    Certain manufacturers offer these devices at around £150 for a Type B RCD rated at 300 mA. That’s 5 x more than the type A equivalent.

    Agreed ... back in around 1988, I installed a single-phase 30 mA RCD (with rated current 63 A) in my Dad's (domestic appliance repair) workshop.

    That would perhaps be described be a "Type AC without current isolation tests and EMC tests, and without some endurance tests (etc. etc.)".

    The equivalent price today would, I believe, be around £300 inc VAT !!! Compare with the price of a current Type A !

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  • in reply to AMK
    AMK said:
    Certain manufacturers offer these devices at around £150 for a Type B RCD rated at 300 mA. That’s 5 x more than the type A equivalent.

    Agreed ... back in around 1988, I installed a single-phase 30 mA RCD (with rated current 63 A) in my Dad's (domestic appliance repair) workshop.

    That would perhaps be described be a "Type AC without current isolation tests and EMC tests, and without some endurance tests (etc. etc.)".

    The equivalent price today would, I believe, be around £300 inc VAT !!! Compare with the price of a current Type A !

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