The caveat with a SMM
is that the frequency has to decrease for it to work unless you are using the generator lockout function.
If the generator engine has more power available than the windings can handle, then it might never drop out.
I believe Generac has their generator's computer (which senses load digitally at the load wires) lower the frequency to 58 Hz on the latest iteration to force the SMMs to trip even if the engine still has enough power, if it sees an overload and wants to drop load.
Portables will not have this function, and may or may not drop load when appropriate, but when grossly overloaded, it should always drop fine.
I installed an EVSE last year, 50A circuit to a 40A EVSE (JuiceNet 40+). My generator (22kW) in my house should be able to take on the EVSE without a problem but because I overdo stuff I shouldn't overdo, I put the Generac SMM in, it's the 6873 model, I believe a 7000 is out now. My plan was to utilize the lockout switch (on) so that the EVSE was locked out under generator power. In my real world it never does. I do not have a Fluke with the proper lineage to measure Hz. But my meter does measure Hz and it shows 59/60 under generator and mostly 60 under utility. If I'm understanding my years on this forum, absorbing knowledge, then my SMM is operating as designed, and my generator is giving me power too close to utility. Again, based on a meter that is not to be fully trusted but it's all I have. Any thoughts? Is this something I should just live with and assume that if the generator gets overloaded it will shed the EVSE at that point? The SMM is under warranty, but I self installed so I don't know how Generac helps consumers working outside the realm of a dealer.