LabVIEW setup for measuring Floating Neutrals

Below is an experiment looking at the voltage drop and floating neutral potential of a 100' extension cord.  Two HP34401 digital multimeters (DMM) are used; one connected from line-to-ground, and the other is connected to neutral-to-ground. 

The first takeaway from this experiment is the line-ground voltage.  At the wall, the line-ground voltage was 119.7VAC.  Looking at the end of 100' of extension cord we now have 118.7 volts, so we lost a volt due to line resistance.  This is actually pretty good, and probably has to do with the heavier gaged wire used in its manufacture.  The real problem here is the ground-neutral voltage.  At the wall, the ground-neutral was 0.65VAC.  As stated in my previous article about 'Floating Grounds', a voltage above 1.0VAC could present problems.  For measurements you'd see unexplained variations in the measurements, and for digital communications you probably see slower transmission rates or communications just stopping as the system struggled to find Logic 0. 

 There's more to this discussion which I'll go into when a get a few minutes.  For now, before setting any systems or taking measurements it is probably a good idea to go to your wall plug and measure what you are working with.  I've seen little things like this burn even the most seasoned engineer.  When dealing with a polynomial where everything is an unknown you solve the easiest variables first.