A pair of RIBS or similar will accomplish all of this and be a heck of a lot easier than a donut on the cable.
A RIB to supervise the loss of AC at the local outlet before the transfer switch and genset kicks in. Easy, the generator is NEVER going to be an instant switchover and start. Tie to a supervision point.
A RIB in a feed from the genset. Hell, if you have multi-phase, put one on each to see where an issue lies.
Leave the fault from the output panel as a general annunciator of issues. Generally a low oil, fail to start, low start battery or similar conditions on most generators.