I've been expanding Insteon throughout my house over a couple years.  I've had my Generac 20Kw with Auto Transfer for this entire time.  Only recently did I notice anything running on insteon switches (mostly LED but also incandescent) flash off/on in unison when running on generator power. 

 

I have a PLM (on a PC)  and hub and both are on a UPS so they can receive signals from wireless only devices while the power is off.  It did not occur to me that the flashing was a result of insteon traffic as suggested in this post.

 

After the blackout I tried to reproduce the effect (only once) by manually transferring to generator power.  I did not experience the flashing.  My previous theory was that somehow the transfer switch was still partly connected to the street, and only when street power was down would the problem exist, but I guess I need to try again and ensure there is insteon traffic to test for flashing.

 

Is everyone certain it's the insteon traffic that is causing the flashing?

 

If you have newer Insteon hardware you can enable the blink on traffic. At that point you can monitor a switch while on generator power and see if the lights flash. Keep in mind this is also very dependent upon the type, brand, and model of bulb in use.

 

If its any kind of LED bulb YMMV so keep that in mind . . . 

I'm 100% certain the flashing I see is Insteon traffic. I press a keypadlinc button, and as each device reacts I get flashing like mad, then it dies down. I trigger a program from ISY to do something, flashing begins again. Task ends, flashing stops. 

 

I'm going to go rent a Honda inverter generator I think, hook that up and power off the main breaker. And then compare. If that solves it, I need a new gen..