Considering that your earth ground is completely separate from the isolated 120V circuit under test, I would not be surprised at practically any readings one might get, and I would not expect the two readings (L1 – G and L2 – G) to necessarily add up to exactly the L1 – L2 voltage (120V). And having L1 – G and L2 – G appear to split the 120V evenly seems a little suspicious. Could there be some inadvertent coupling going on?
That said – remember that by taking measurements, you are in effect making a connection that did not exist before the measuring operation - albeit a very high impedance connection.
Are you taking your readings on an open circuit? Or is there some load? Would it make any difference? I don’t know. Try it both ways and see.
I recall in Navy shipboard electrical systems, which are intentionally UNgrounded, you could still get a good jolt by touching a leg of the 120V system and any exposed metal around (i.e. – earth ground, so to speak), due I suppose to capacitive coupling.
Working with ungrounded (isolated) circuits can be fascinating – definitely a little different.
Thx.
