I just returned from a call where the complaint was intermittent shocks being received from the plumbing. I proceeded to amp out the neutrals and GEC. When the air handler is running there is 7 amps returning from the sub panel to the main neutral bus. However, 2 amps of the 7 leave thru the GEC which is bonded to the water pipe. The other 5 leave thru the main service neutral. I re made all the neutral connections in the panel, meter base and weatherhead. There was no change. My thought is a high resistance connection at the pole mounted transformer, so I called the utility to check.
I ruled out any interior connections as the full 7 amps appears in the sub panels neutral, it does not divide till the main.
Barring a hot wire touching a pipe somewhere, am I on the right track here?
Just a shot,is the house fed by a well?If so is there a water softener? If so check to make sure the outlet for the water softener controls is actually 120 volts from a true 120volt circuit. Water softener companies around my part like to do their own electrical and steal a leg off the 240volt well circuit and use the ground for their neutral. Just a shot but it might be as simple as that.
I know the dirt is not supposed to be a current path but there is really no way to stop it. When the ground is wet around here I have a few amps on my GEC too. If I go out to the pole and look at the ground wire coming down to their rod it is carrying a similar current.
If this buiding is served by a metal underground water pipe system and there are other buildings in the area, it may be normal. Under these conditions the metal underground water pipe is connected in parallel with the grounded conductor per the code rules. Don
Don, I understand how there are parallel paths here, I just thought that 30% of the return current seems high. But if I really think about it, if the water piping system was in great shape electrically, it could conceivably carry half the neutral load! This seems a bit scary to me! But the only reason I can think of why the current would back up into the house plumbing is a bad connection at the service neutral. Sure maybe 2 amps is acceptable at the GEC, but not at the kitchen sink!
Jon, I did pull the meter and the neutral current dropped to zero on all conductors. That is how I verified the current was from the dwelling in question.
Once the POCO re splices I will have to go from there. Maybe I will have to start looking to see if someone lost a neutral and tagged on to a water pipe to fix it. The whole house is two wire, no grounding conductors.
There are three common items I know of that cause this problem
1. Metalic water pipe between houses/buildings with a common transformer serving them and one house has a high resistance grounded service conductor.
2. A high resistance grounded service conductor, simular to # 1.
3. A very low ground electrode impedance.
First thing I would do is turn off all the breakers and determine if the current is from an outside sources (like comming via water pepe) or generated within. That would give you a good starting point.
I did turn everything off, the current disappeared. Current appears whenever any load is turned on at the home, indicating it is from within that home. I am going back next week after the POCO has been there. Maybe like Don said this current is normal, but if the neutral connection was bad wouldn't this cause it to back up into the house plumbing since the water pipes are most likely also high resistance from all the connections/meter etc?