Two dedicated AC combiner boxes are in the recommended configuration for running two EG4 18Ks in parallel. This seems to be different from a PV combiner box which I think operates at lower voltages. Is this just a box containing taps to split the 120v P1 and P2 on input side, and another box containing a tap to combine the neutral on the output side? Or is it an actual device one can purchase? My searches have only turned up PV combiners...