I had an inspector come out to a house and met with one of my guys on a final.
He plugged into a 1/2 switched outlet (switch in off position) with a real fancy Ideal arc fault/GFI tester. The neon lights on the tester glowed dimly and he made the statement that there seemed to be voltage on the neutral. The regular GB outlet tester had no lights glowing at all.
I went back to the house with my guy and we started checking out the circuit. We put the digital meter across the switch leg and the neutral and across the switch leg to ground and got about 40 volts. We went through the whole house checking the same way and found this to be true on every 1/2 switched outlet.
We took a piece of 14/3 NMB about 20' long and hooked the black and white to 120 volts and what do you know? The red wire had about 40 volts on it.
The last couple of days we've been checking every 1/2 switch that we ran across just to see. It always has about 40 volts on the switch leg with the switch off.
As this does not seem to be due to any sort of wiring defect such as too tight on the stapling or a tab on the receptacle not cut all the way I'm assuming that the red wire gets partially energized by induction or something. I'm no engineer. Just a guess.
There is no real potential present as you can touch the wire to the ground or neutral and there is no indication of a spark or anything.
I was looking for some input from others who may have experienced this occurence.