Backstory: I am running power (temporarily) to a workshop through a 25' and a 50' extension cords. I was worried about the voltage drop over this length so I was measuring voltage to see if it dropped below what the tools needed. As it turned out, there was almost no voltage drop, which really surprised me, so I connected another 50' cable to the end of that. Still no very little voltage drop.
The resulting daisy-chain looks like this:
Outlet -> [25' 10AWG] -> [50' 12AWG] -> [50' 14AWG]
Then I decided to measure neutral to ground to see if it was zero. I tested at each of the four locations, and had various readings from 8V to 0V. It seemed that the farther I got from the original outlet the higher the voltage. What can explain this?
Best Answer
Keep in mind that voltage drop in the wire is totally load dependent; when you measure voltage without load at the end of long wires, you won't see much if any voltage drop. If you use a splitter on the end of your chain of extension cords, and plug in your shop vac and turn it on, and test voltage on another receptacle on the splitter, you'll see voltage drop.
The small voltages you're measuring from neutral to ground could be induced voltages, and will disappear if any load is placed in the test circuit, or if you use a low impedance volt meter, which is in itself enough of a load to make the phantom voltage vanish.