The previous (pretty old) thread on this subject didn't really answer the question, so:

I just disconnected a ground wire that runs between my main breaker box and the cold water (copper) line. The disconnect was at the water line, and significant sparks fly every time I touch the ground wire to the pipe. And, when connected, it cause the lights in the house to dim appreciably.

I measured the voltage between this ground wire and the water pipe and it's running at about 9.6VAC.

Would this explain why I've thought for years that my electric bill was too high?

How do I go about isolating the source of this faulty ground?

No, this current will not affect your electric bill, you paid for the power once, and that's all you pay for. Your electric bill is too high because of the appliances, lights, etc you have. Time to get this under control. Change to compact fluorescent lamps, adjust water heater settings, shut things off that are not needed, etc.

The fault current is from most likely a refrigerator or fluorescent fixture. Can be from anything, but those are the popular devices that normally have fault currents.

You need to keep the ground wire on the water line until your ready to trouble shoot this situation, or it is possible someone can feel this voltage when using any applaince and touching the water lines, like a faucet.

To troubleshoot this, first you need to shut off one breaker at a time while testing the voltage, then once you have it tracked down to one or more circuits, then find the device or appliance that is causing the fault current.

What to then will depend on what is causing the current.

One breaker at a time doesn't do it. The problem doesn't go away until I turn off ALL the breakers. Then, turning on ANY ONE breaker causes it to resurface. So, there's somethng very fundamental here that I'm missing.

Ok then the problem may be a neutral wire is connected to the equipment ground someplace, either by a short or mistaken/intentional. Or the grounding is loose or not done correctly in the panel, meter, or even a loose connection outside at the utility connections.

I suspect the main neutral conductor is loose somewhere, causing the ground to carry some of the return current.

You know, there is a possibility the water line has the voltage on it, due to a problem with some appliance or a neutral/ground short.

This troubleshooting is beyond the ability of a layperson. Involves opening the panel and possibly the electric meter to check for all proper wiring and loose connections, and may need the utility to check their equipment.

You should call in a qualified electrican that is proficient at service and troubleshooting. Have the source of the ground voltage checked and corrected. Good time to have all your equipment checked for proper torqued connections.

Let me know what is found.

All good possibilities, except the water line being hot. It's not connected to anything at all at the moment.

I'm in a deadline crunch to get the walls bared back to the studs but as soon as that's done I'll investigate this more and let you know.

There is only one answer to explain this. The sparks that you notice are caused by current. Current flows in the most direct path back to the source (which is the outside power supply).

The copper pipe is grounded but is connected to the outside supply by earth which is resistive (between 5 and 20 Ohms).

Normally, the neutral is grounded but is connected to the outside supply by a connection that has negligible resistance. Thus, current will take the neutral connection back to the supply and the copper pipe will carry no current.

So the Neutral connection from the panel to the outside supply must be faulty (and be resistive). This is how I would troubleshoot the problem:
1) Remove and reterminate the supply neutral conductor to the neutral bus at the panel. Make sure the connections are clean and tight. Measure voltage at copper pipe (better yet, measure the current).

If no change, call the electrical utility to check the problem.

This is a serious problem and will lead to pre-mature failure of electrical equipment and possible shock and death to people in the house.

Please get it fixed.

As a side note, I believe that this ground current will affect your electricity bill. Appliances will be running less efficiently, at a lower voltage and higher current. Your electricity bill is based on current at the meter. The more current, the larger the bill!

This would only apply to 120V appliances and should not be that much of an increase. The main worry is the shock hazard and electrical devices burning out.