NopeShould preface this by saying I’m not fully qualified yet - just waiting for nvq 3 from my employer!
But rcd discrimination would ensure garage trips first if there’s a fault there no? Correct me if I’m wrong !
Why would any particular rcd go?
In effect you have two devices in series, both operate at 30mA with the same time setting.
If anything, the upstream one is likely to operate first.