ground is not universal. it does not mean 0 volts. something is considered grounded if it has the same electric potential as "ground" or common or something like that. your tank could be carrying potential that turns into current when given a return pathway like you.
Would you believe I have a college degree in electrical engineering technology?
You are exactly right.
Which is why I bonded my meter back to the house main earth ground in the yard. There is no more zero than the Earth.
With that as my zero point I can detect voltage on anything, even the neutral.
The screw I am reading voltage on goes through a plastic cable tie and into wood siding and I know what is behind it because I put it up myself. It has to be induced voltage.
Now I will tell you something creepy. I have been shocked thousands of times on the job. I worked for the phone company. All sorts of circuits from POTS lines to high speed digital to control circuits for motor controllers for leasees
run in phone cables. When you go to repair a damaged cable on a rainy night they knock the snot out of you.
Nothing gets turned off. If you are up on a pole or ladder with your arm over the steel carrier that holds the weight of the cable that is grounded every live circuit you touch puts power in your fingers and it comes out your armpit. If you are sitting in a mud hole repairing a burried cable you get shocked in the butt or feet.
T-1 digital lines have +60 to -60 volts on them so you get hit with 120 volts. Ringing voltage is -48 volts. Everyone is calling their mom to see if the phone is back on yet.
And the best one was hooking up rural lines that run parallel to a power lead going to a house or barn in the country, sometimes for miles. The induced voltage in those lines rises to the value of the power line so 480 volts sometimes. You are trying to hook a wire up and it is arcing to everything it gets near. You can write your name on a piece of metal with it.
But after all that I am still here. I don't think my fish tank is going to get me.
Now that I think about it the screw is probably being induced by the transformer it is next to that it is holding to the wall.
I am not as quick in the head as I used to be.
they did show not too long ago...???
