I had my neighbors wife tell me she had been shocked several times when touching her cooktop and sink when the water was running. Home built in the mid 1940's original GE pink appliances and still going. I went and discovered with the cooktop off and measuring the voltage to the metal drain pipe (after the plastic trap etc., not original) 3.4 volts. With the top on 74 volts.
Additional information: No main on the house two-wire typical wiring without ground, FPE panel. The water lines connecting the sink were also replace with plastic tubing.
Checking things out I found:
Several grounding style receptacles that had replaced original non-grounded receptalces with grounding conductors added but just loosely wrapped around metal water pipes. I added pipe clamps.
They added a new bathroom and the plumber changed the piping at the water heater to plastic tubing, thus breaking any bond between the hot and cold water. These are now bonded together, noting that the above receptacles wires had randomly selected either hot or cold piping.
I got into the panel and found all copper wiring, I was surprised and pleased. But I needed to go through and retorque everything. The worst was one of the service line conductors was so loose as a light pull would have removed it from the lugs. The family is living right though as there was no heat damage to the conductor. I exercised all the breakers and left the panel feeling that the FPE panel was in good condition.
Pulling the cooktop I found no option for pulling in an equipment grounding conductor as no bonding point was provided and the nuetral bonding point must of been located somewhere deep in the appliance or possible in the separate control unit which I did not desire to try to remove it from the wall (read as: I was not smart enough to figure out how). Well, giving up (and still with the problem) I start to put things back together. I pull out the noalox (conductive antioxident for AL conductors but works for CU) and individually coat the multiple (about 12) prongs in the connector in the hopes that a poor nuetral connection may possibly be improved. Finished up thinking I would need to tell them that they needed a new cooktop and found to my joy 3.4 V on the cooktop on or off.
It feels nice to save someone money, home, and possibly lives. Now to see how long this fix will last. They are starting a savings program for replacement.
When I moved into this house I was getting shocks from the cooktop to the terrazzo floor if I was barefooted. I fixed that by repairing the ground electrode system but along the way I found numerous other grounding issues. One thing I did figure out was that there was a ground wire in the 8/3 romex serving the cooktop, it just wasn't connected. They had the old style 3 prong plug and only connecting to the neutral. Once I got the EGC connected at the panel end I lifted the bonding strap in the cooktop and extended the EGC right to the top surface sheet metal. No more shocks.
I can't tell you how many times I've encountered this in the past. The frame bonding to the neutral that used to be allowed was always the culprit. Since the neutral isn't really needed in a typical range, oven or cook top for anything but the lights, clock, etc., the leaks were always strange voltages.
Since a cook top rarely has any 120 volt requirements, I often wonder why there is a need for a neutral to be provided at all.
My question here is where was that stray voltage to ground coming from? A failing element? That is the only thing that I can think of, especially in such an old cook top.
The best I could determine the leakage in my cooktop was from the large front element. That seemed to be the one that that was on when I got the buzz. I did not screw around with it very long and went right after the grounding. Shortly thereafter that element failed which further confirmed my suspicion. I certainly do not believe that simply because the utility is supposed to ground the neutral, that insures it is really at zero volts compared to the slab under your house. That is particularly true if you have wye distribution since the neutral on the pole is a current carrying conductor
The age of the house is suspect, not neccesarily another remodel. The stove elements all looked in excellent shape but I did not think to test them.
I do know that the contacts at the plug to the control panel were poor, otherwise I would not have seen the improvment. Could also be some leakage due to insulation breakdown elsewhere in the appliance. Like I said though, their savings plan now includes a new appliance plan.