T(or rather, on a recent day)IL: If you have an electronic device with more than one fuse, you should galvanically isolate (e.g. via optocouplers) signal lines between the areas powered via those fuses. Otherwise, if one fuse blows, you'll end up powering the part of the circuit behind the blown fuse via signal lines and ESD/overvoltage protection diodes (that are connected from the signal lines to positive power rail, to limit the voltage on the signal line).

You _can_ get away without galvanic isolation (e.g. by putting resistors in series and accepting the current that can be drawn through that resistor at ~your VCC), but that is harder to reason about, and potentially requires testing of many combinations of blown fuses.