Mike, will you explain the problems that may occur (if any) if somebody were to use a generator for the main power source and also using an outlet from the house power at the same time? Is that a bad idea?
Thanks
I'll add more to this later, but for all the reasons that TJ has noted, there's lots of potential audio noise and life-safety issues if both house and generator power grounds aren't tied together properly. And that ground/bonding wire needs to be as heavy as any of the potential mains currents. So a piece of #8 or even #6 wire is the traditional gauge required. I've done outdoor gigs with generators and wondered why my XLR cables were getting hot. Now I realize there was probably a LOT of grounding current flowing between various pieces of ungrounded/unbonded gear.
Of course, any ground loop currents flowing through the shields of an XLR cable can cause hum due to the pin-1 problem which still exists on a lot of modern gear.
So the short answer is this. Unless you know exactly how both generator and house power is grounded, then it's safest to pick one or the other. I can also visualize a really crazy ground-loop condition that would have very low frequency currents from the non-phase locked systems. For instance, if the generator was running at 61 Hz and the house power was at 60 Hz, then there could be a 1 Hz loop current created that could do some crazy stuff like resetting computers, making light dimmers slowly shift intensity, and heaven only knows what other kinds of problems.