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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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  • My understanding from IET presentation is that they can can create up to 5mA DC leakage under normal operating conditions and the value can change depending on what car is connected. Therefore it can't be considered a fixed value. If we are looing at multiple charge points it's likely to be a commercial install and extra costs accepted.

    But for private residential the industry is creating an expectation of  installation costs in the region of £300 to £400. Then I come long and say because of over head lines, TT earth and submains I need an extra £300 for type 1 spd, £250+ for type B RCD etc. I am sure many of the big companies will just chuck a EVCP in, no spd and single type A RCD/RCBO if you are lucky.

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  • My understanding from IET presentation is that they can can create up to 5mA DC leakage under normal operating conditions and the value can change depending on what car is connected. Therefore it can't be considered a fixed value. If we are looing at multiple charge points it's likely to be a commercial install and extra costs accepted.

    But for private residential the industry is creating an expectation of  installation costs in the region of £300 to £400. Then I come long and say because of over head lines, TT earth and submains I need an extra £300 for type 1 spd, £250+ for type B RCD etc. I am sure many of the big companies will just chuck a EVCP in, no spd and single type A RCD/RCBO if you are lucky.

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