I know that what I am about to tell you can be dismissed as anecdotal but I have personal experience with getting a shock from a generator. While operating at a pier fire in San Francisco as a member of that cities Fire Reserves I was assigned to deploy a Circle D flood light down the side of the pier shed. As I was maneuvering around an obstruction at the edge of the pier deck I received a shock that prevented me from letting go of the flood light. I still had control of my other hand so I was able to hold on to the obstruction and avoid falling into the harbor. Once I had stumbled or fallen back to level pier deck I used my free hand to unplug the cord from the Circle D light. I don't want to think about what would have happened to me if I had fallen into the harbor with my left hand locked to the handle of a faulted flood light. The generator set was quite large as it was the departments special light and power unit. The neutral was bonded to the frame. The cord was two wire with no Equipment Grounding Conductor. The generator frame was not deliberately earthed but it may have been bonded to the truck frame. One possibility was that the other equipment deployed from the unit may have been the other side of the circuit but wouldn't that have meant that there were two complimentary faults in two different items. If one of the other loads had an Equipment Grounding Conductor that might explain the return path. Both the fireboat Frank White and the Fire Boat Phoenix were pouring thousands of gallons of salt water onto the pier. We had been operating for over six hours at that time and I was soaked to the skin. The conclusion I drew from that experience was that if the neutral is to be bonded then the equipment should have an EGC. Conversely if the neutral was not to be bonded then it should supply double insulated portable equipment only in order to insure complete isolation under real world conditions.
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Tom H
