Here's an email we got from one of our Instructors:

I just purchased a portable generator from Harbor Freight and was reading my operating guide for the machine.  The instructions said to ground the generator prior to use and this seemed strange to me, since I would be using the 4-prong 240V connector to my house.  I asked an electrician at work, and he recommended that I not add a ground, and to watch your video on grounding.  Very informative video.  As advised by the instructor in the video, you, I am informing you that there is another manufacturer that is recommending grounding their machine.  Attached are the instructions.

Thanks for the education,

Stewart

Mike Holt's Comment: See my Electrical Safety Fundamentals [1hr:13min] video on Grounding.