Shore power and generator

lj2654 wrote:
Isn't it possible for a transfer switch to fail causing dual power from the shorepower source and the genset source potentially starting a fire. For that reason I always disconnect from shore power before turning the genset on hot.

No. The transfer switch is designed precisely to make that impossible; that indeed is its primary mission in life. A transfer switch that allows both inputs to be connected simultaneously under any circumstances--including ordinary sorts of failure modes--is a dangerous device and likely would be recalled, just as a circuit breaker that fails to trip under overload conditions would or at least should be.

More likely than a fire hazard is severe damage to the generator and possibly surrounding parts of the RV as it self-destructs. The generator's alternator works equally well as a large electric motor, and if the phase of the generator and the shore power are not synchronized (and they almost certainly would not be), the shore power will nearly instantaneously shift the generator's rotating parts to match it. This causes huge stresses and things breaking and flying off. There are cases of unsynchronized hydroelectric (and other) generators being improperly switched into the grid and causing their rotors to fly through the walls or roof of the generator house. The same thing could easily happen, on a smaller scale, if the generator and shore power were connected together.

Even if the generator were not running, there's a very good chance that connecting shore power to it would cause it to spin and work a good deal of mischief.