It doesn't appear that I can edit my first post, so I will add this:
I'm not a licensed electrician. I haven't done apprenticeship or gotten a license, and I certainly don't know the code as a licensed electrician should. I'm a career Navy electrician, which is different. I learned to work safely with electricity in the Navy, but our work was more often on nuclear propulsion related motors and controllers, valve controls and valve position indications, turbine generators, diesel generators, DC motor driven AC generators, some of which could reverse mode of operation and charge the main battery from the main AC bus from turbine generators, diesel generator or shore power, and on submarines we also owned the ship's main battery, galley equipment, laundry equipment and lighting wiring.
On ship, the electrical system is technically "ungrounded", but you have "Earth" ground all around you. There is also 3 phase 450VAC, 120VAC, 270 VDC, 120 VAC 400 HZ... If we needed to measure resistance to ground we could just touch a meter probe to any nearby piece of metal.
In my old home though, I sometimes have to hunt for an "Earth" ground like the copper water pipe. I've also had to learn some nuances working on outlets and code compliance that are different.