How dangerous is it to leave 35KVA diesel generator ungrounded?
This generator is connected to temporary metal buildings for workers, AC and other electrical devices.
"not grounding things" has been tried. Gets people killed. The problem is, what happens in case of a ground fault? That is where current leaks from one of the hot wires to a surface you can touch. What keeps a ground fault from energizing the entire side of the building?
Without a proper ground, you leave to Providence what happens next. And lots of people get electrocuted this way, and it starts fires. Your generator has a steel skid or landing gear, yes? What happens when it rains? Now the impedance between your building and generator case is much lower, and now electrocution risks exist that weren't there in the dry. With a ground,
Why not an isolated system? Two problems. #1, you need a maintenance program wherein staff electricians regularly checking for your first ground fault, or else you'll be blindsided by the second that completes the circuit. #2, you must engineer it to be an isolated system, which means you can't use common, off-the-shelf gear intended for grounded systems - it is disallowed to use gear contrary to its labeling and instructions (since it was only tested and listed for uses conforming to the instructions). The world of the Electrical Code is based on hard-won experience.
It depends on the generator but they do not recommend grounding 'for fun'
I would strongly suggest you ground it, so you don't get all kinds of random stuff happening, or worse, people getting killed.