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Selectivity of RCD types

Former Community Member
Former Community Member
In this Voltimum article https://www.voltimum.co.uk/articles/could-rcd-type-s-be-used-upstream-rcd, it discusses some aspects of selectivity of RCD's with regard to different types as follows:

1. A type ‘A’ RCD should not be fitted upstream of a type ‘F’ or ‘B’ RCD.



2. A type ‘AC’ RCD should not be fitted upstream of a type ‘A’, ‘F’ or ‘B’ RCD.



3. A type ‘F’ RCD should not be fitted upstream of a type ‘B’ RCD.




What is the danger of fitting a type A or AC RCD upstream of a type B RCD?

It talks about the smooth DC current blinding of the Type AC, but surely thats the point of the Type B RCD? If a smooth DC current appears from down stream of the Type B, then the Type B will open, leaving he rest of the installation safe? What am i missing?


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    You can have a DC leakage current which is too small to trip the B or whatever, but is still large enough to blind the AC or whatever.
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  • 0
    You can have a DC leakage current which is too small to trip the B or whatever, but is still large enough to blind the AC or whatever.
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