How to tell if your AC wiring needs an upgrade

 

The final 0.4V reading could be nothing more an induced voltage by the HOT 120V ungrounded conductor.

I suspect the 0.9V was not correct and was influenced by noise pickup. The 0.4 is likely the accurate measure.

@erik_squires understood your meaning now.  You are using the ground-neutral voltage as a crude ammeter.

The higher the neutral voltage the lower your outlet voltage (assuming you don't have something else wildly wrong).

Can you explain this above?

I did the test with a multimeter on kitchen outlets with nothing connected. I measured 0.9V. I plugged in a 25W incandescent lamp and the voltage dropped to 0.4. Was the 0.9 noise?

I am now down to <= 0.1  The poor old Fluke had been dropped one too many times.