The shore power should not run straight to the bus powering the circuits.
Ok, I'm not educated on what a PO did or your particular panel (post a pic?) but, generally, the shore power cable runs to the panel main breaker, which feeds the bus that feeds the various breakers/circuits/equipment (like water heater.)
That's "generally" - on my '84 panel for instance there's no bus; the 30a Main feeds to the Pos and Neutral terminal strips and individual fuses are wired to the Pos terminal strip.
Ok, I'm not educated on what a PO did or your particular panel (post a pic?) but, generally, the shore power cable runs to the panel main breaker, which feeds the bus that feeds the various breakers/circuits/equipment (like water heater.)
That's "generally" - on my '84 panel for instance there's no bus; the 30a Main feeds to the Pos and Neutral terminal strips and individual fuses are wired to the Pos terminal strip.