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RCD Types for EV Chargers on TT systems

Former Community Member
Former Community Member

On a TT install, where the supply for EV chargers comes from a feeder pillar. If the EV charger has a 30mA Type B RCD, is there a requirement for an upstream 300mA Type B RCD or can it be a different type? 
Can I specify 300mA RCDs as the main switch (is this type B?), and what would the solution be if I wanted a 250A incomer, would I then need an additional upstream type B RCD for each charger between the distribution board and the charging unit. This is a very expensive component if needed.
Siemens and an article from Voltimum have indicated that the upstream RCD needs to Type B and the code of practice shows a 300mA RCD upstream on a diagram but not which type. 
Looking for some guidance on this and an explanation if possible.

Thanks

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    I thought the problem was that 30mA B-type RCDs might not trip until the d.c. residual current reaches 60mA - whereas 6mA d.c. might be enough to interfere with the operation of A-type RCDs.

    In some ways the RDC-DD solution is better as it limits the d.c. residual current (from that one charge point at least) to 6mA rather than 60mA - thus allowing A-type RCDs to be used upstream.

    Hence the general rule that if you need a B-type at some particular point, then likely you'll need B-types upstream of that.

    It gets even more complicated where you have multiple charge points fed from a common upstream RCD (individually each charge point might have a d.c. residual current <6mA but that might add up to something well above 6mA). Also the 6mA and 60mA figures might not hold true for higher rated RCDs … but what the equivalent numbers are seems to be hard to find.

       - Andy.

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  • 0

    I thought the problem was that 30mA B-type RCDs might not trip until the d.c. residual current reaches 60mA - whereas 6mA d.c. might be enough to interfere with the operation of A-type RCDs.

    In some ways the RDC-DD solution is better as it limits the d.c. residual current (from that one charge point at least) to 6mA rather than 60mA - thus allowing A-type RCDs to be used upstream.

    Hence the general rule that if you need a B-type at some particular point, then likely you'll need B-types upstream of that.

    It gets even more complicated where you have multiple charge points fed from a common upstream RCD (individually each charge point might have a d.c. residual current <6mA but that might add up to something well above 6mA). Also the 6mA and 60mA figures might not hold true for higher rated RCDs … but what the equivalent numbers are seems to be hard to find.

       - Andy.

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