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RCD for use with DC leakage

Mspark

Proposed installation of EV charge point with two socket outlets on same charger. Manufacturer claims maximum DC leakage current no more than 6mA from charger.

Installation is a small hill farm with multiple armoured submains to outbuildings. Whole site is TT earthing system with an existing 100mA (s) Type A RCD main switch.

One outbuilding has 4kW Solar PV with inverter no simple separation manufacturer claims maximum DC leakage current no more than 6mA.

With the addition of an EV charge point to an existing submain on a remote building there is the possibility of EV leakage 6mA + PV leakage 6mA =12mA of DC leakage current which may blind the RCD main switch. I have tried to locate a 100A single phase time delayed type B RCD suitable for operation by an ordinary person but have failed however I have found a Schneider A9R35291 100A 300mA  (s) type A super immunized which is suitable for use with DC currents up to 60mA.

The Schneider information says it has proposed another possibility with the use of this product and does fit with my installation requirements.

I'm not sure where I stand when the wording says proposed another possibility.

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    I was under the impression that the DC leakage happens under normal operating conditions

    We debated that a while ago - and I think didn't come to a complete conclusion. Certainly it's easy to see how larger d.c. residual currents can occur during some simple faults (e.g. shorts between power and pilot conductors in the EV lead), it's less clear how we'd get d.c. residual currents in normal operating conductions - e.g. the 'leakage' due to capacitors (e.g. noise filters) that we're familiar with on a.c. systems presumably wouldn't pass much in the way of (pure) d.c. (I suspect we'll end up replaying the debate from last century about direct current vs continuous current, i.e. where currents vary cyclically over time but not to the extent of reversing polarity). If anyone has any definite knowledge of the d.c. leakage characteristics of EV chargers in ordinary operation, I'd be very interested...

              - Andy.

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  • 0

    I was under the impression that the DC leakage happens under normal operating conditions

    We debated that a while ago - and I think didn't come to a complete conclusion. Certainly it's easy to see how larger d.c. residual currents can occur during some simple faults (e.g. shorts between power and pilot conductors in the EV lead), it's less clear how we'd get d.c. residual currents in normal operating conductions - e.g. the 'leakage' due to capacitors (e.g. noise filters) that we're familiar with on a.c. systems presumably wouldn't pass much in the way of (pure) d.c. (I suspect we'll end up replaying the debate from last century about direct current vs continuous current, i.e. where currents vary cyclically over time but not to the extent of reversing polarity). If anyone has any definite knowledge of the d.c. leakage characteristics of EV chargers in ordinary operation, I'd be very interested...

              - Andy.

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