Presumably you meant BS EN 61008 if you were referring to an RCCB. BS EN 61009 is an RCBO. (Both are 300mS though. It's the non-EN Standard ones which are 200mS, as you are obviously aware.)
I understood, but was coming from a different angle. If I ask can we have abc and they so no because of xyz then u can be confident it's a considered response based on some testing/investigation. however if they answer we usually do 123 not abc because it's quicker/easier/how we do things then it's not.
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