Interesting Ground Experiment

[ddawg16]

I was disconnecting some wires in my load center yesterday in order to cover up a hole in the wall. In the process I had to temporaily disconnect my ground wire....that 4awg wire comes from the front of the house where it is connected to a ground rod and my water pipe.

Well...while I had the wire off I thought I would measure the voltage between ground and neutral...

0.14 VAC

And that is without my house being grounded. What does this mean? It means that all of the outher houses around me on the same transformer are properly grounded. That is a good thing.....It means that I'm not the sole reference for neutral to ground....

 

[MrMark]

The transformer is referenced to Earth at the neutral (center tap) at get around 0V. Your neutral just floated a hair, no biggie. I don't understand the last part of your comment. Why do you think your experiment proves that the other houses are properly grounded?

 

[MrMark]

Many of the houses around where I live (Compton Ave.) never had any ground rods and they all work. The system does not depend on the ground reference at the houses to work. A little float never hurt anyone.

 

[mrb]

when disconnecting the water pipe bond its smart to throw a clamp on ammeter before detaching, and dont become a path between what you disconnected.
Here's a scenario: neighborhood has metallic water piping. You have a bad (open, or loose connection) neutral between your service and the poco transformer. The current that should be flowing on your neutral is now traveling out your water line, across the water main, back up your neighbor's water line, across his water line bond and out his neutral back to the transformer. You disconnect your bond you didnt know was carrying current now you have a high potential difference where you disconnected it posing shock hazard not to mention potentially damaging electronics in your house due to voltages increasing and lowering without the neutral connection.

 

[MrMark]

Truer words have rarely been spoken. I always do the above. Even do that with metal conduit before taking it apart.

 

[mrb]

Even do that with metal conduit before taking it apart.

yeah, i almost killed myself with that one....

 

[Alchymist]

when disconnecting the water pipe bond its smart to throw a clamp on ammeter before detaching, and dont become a path between what you disconnected.
Here's a scenario: neighborhood has metallic water piping. You have a bad (open, or loose connection) neutral between your service and the poco transformer. The current that should be flowing on your neutral is now traveling out your water line, across the water main, back up your neighbor's water line, across his water line bond and out his neutral back to the transformer. You disconnect your bond you didnt know was carrying current now you have a high potential difference where you disconnected it posing shock hazard not to mention potentially damaging electronics in your house due to voltages increasing and lowering without the neutral connection.

You lose the neutral connection to the POCO and you got more problems than worrying about disconnecting the ground - things will start popping as soon as that neutral is lost. The neutral is what provides the 0 reference for the split 240 volts - holding it at 120 each side. Lose it, and the "ground" system won't hold the neutral at the panel at 0. How much it deviates is a function of how good the ground system is, but it's never good enough to avoid some damage. This is particularly true in areas where houses are farther apart, or don't share a common metallic water system. Many houses today don't have metallic water lines - all plastic. GFCIs will start tripping also, as the line/neutral balance is disturbed. And if you should choose that moment to disconnect the ground wire - you are right on that point, it will carry a high potential.

All the more reason for getting the POCO or an electrician involved when things start acting weird.

 

[mrb]

You lose the neutral connection to the POCO and you got more problems than worrying about disconnecting the ground - things will start popping as soon as that neutral is lost. The neutral is what provides the 0 reference for the split 240 volts - holding it at 120 each side. Lose it, and the "ground" system won't hold the neutral at the panel at 0. How much it deviates is a function of how good the ground system is, but it's never good enough to avoid some damage. This is particularly true in areas where houses are farther apart, or don't share a common metallic water system. Many houses today don't have metallic water lines - all plastic. GFCIs will start tripping also, as the line/neutral balance is disturbed. And if you should choose that moment to disconnect the ground wire - you are right on that point, it will carry a high potential.

All the more reason for getting the POCO or an electrician involved when things start acting weird.

in dense neighborhoods like the OP and I live in (provided there is metallic water piping) you can lose the neutral and never notice until the water pipe bond is removed or the water pipe is seperated. There was a plumber killed by this once.