I need to connect this to existing normal breaker of 30A.
I can't use a breaker panel because it would mess up the existing amperage. I just need the GFCI function of the above (especially its superior automatic self-test that isn't available in any 240v 2-pole receptacle). Any idea how to connect some kind of metal interface or adaptor to the plug-in conductor portion? I have to build one since a commercially available adaptor doesn't exist. Then I'd series it with existing 30A breaker load side (which is also 2-pole).