I am actually a pretty good electrician, but am baffled by what I found today.
During a remodel and adding a few new boxes for future lights, I received a shock from a neutral wire and a floating ground.
The house is old and there are no grounds on most of the circuits. I was confused for there is no ground except for about 20 ft going from one new box to another but not connected to panel ground. In fact the ground is terminated with a wire nut in each box but are not connected to anything. Yet when I tested the neutral to ground voltage, I found 48 volts.
Subsequently I tested a few other outlets in the house and also found neutral to ground voltage of 48 v. I then unplugged all devices. Voltage to ground disappeared. Only when I plugged in a device with a ground did the neutral to ground voltage reappear. I then went to the main panel thinking I had a bad neutral somewhere, and disconnected each circuit one at a time and found no neutral to ground issues at the panel and the neutral voltage only disappeared when I turned off hot to circuit.
Different circuits were found to have neutral to ground voltage only when a grounded plug was put into that outlet. I assumed that the ground of the device was allowing me to read neutral voltage. Hot to neutral is correct everywhere. I am baffled. Suggestions?
Best Answer
The AC input circuits of some devices use a power line filter circuit that works to keep high frequency stuff inside the equipment and prevent fast spikes from entering the product from the power lines.
The schematic of a typical power line filter looks like this.
The two capacitors that you see in the filter from line side to earth and from the neutral side to earth can form a voltage divider for AC voltage and place approximately half the line voltage on the earth wire. This would be the case for instances where the earth ground connection was open circuit.
Normally this is not a shock hazard issue because the neutral wire is shorted to the earth ground connection at the power panel.
The fact that you found this AC signal present demonstrates that some part of your house wiring has a open earth ground wire someplace. For the safety of your self and your family it is essential to get this fault corrected. The floating earth wire is an invite to it not performing its safety function when you least expect to need that safety feature.