ELECTRICAL GROUNDING

Jackmartin

Hello from Winterpeg, it is 8 degrees for Easter and someone forgot to tell the weather station is is supposed to be spring, so Happy Easter anyway. Our eldest son, asked me to pop over to his house, as he had an interesting problem. He is an electrical engineer and he works designing transformers for the power industry so this is something he deals with on a day to day basis. He had borrowed my clamp meter so he could take some amperage readings and he found something that I had never heard of before. Now, I should state here, I have had a lot of experience with primary wiring as my old man was an electrical contractor and since I was free labour, I have been turning a screwdriver since I was ten. The nicest thing my old man ever did for anybody was die, please stay that way Dad.
However, I digress, my son takes me over to the earth ground for his house, in this case the cold water pipe coming in from the street, and puts the meter on the grounding wire and it shows 1.8 amps. I have a brand new Fluke, since my old Analog Amprobe gave it up, so we knew the meter was not at fault. I have never seen this much amperage at the water line ground, or should I say, I have never seen any readable amperage at this point.
He then tells me we are going to kill the power to his panel and test it again, with the main disconnect off, the amperage reading on the water pipe was 1.6 amps. I told him I had never seen this before and he started to explain it in Engineering terms which is all mathematics and I had to tell him I took Calculus forty years ago so speak in English. He says electricity will take any path available to it and that means of course the path of least resistance. The way this old transformer is hooked up at the pole [ he lives in a house one year older than ours 1912] the grounding of the transformer is no longer legal for new installations because you get back feed from the transformer grounding back into the panel, it is the nature if the beast. He told me he was so confounded at first, he asked the old guy at work, who as he puts it "knows everything" and the chap was nice enough to draw out what was happening. Now, we come to the reason for this post; his mentor at work told him if you removed the bare copper conductor at the water pipe the voltage would instantly spike to 120 volts because it was being back fed. In the event you think I have been smelling to much pipe dope, we shut the main off in the house and we took an amperage reading at the bare ground where the Hydro service comes into his house and it read 1.8 amps no draw from his panel, and of course we got zero amps on the two power legs.
The reason I am going to this length to explain what I have just seen; is about everyone going home when the day is finished. The point being, if for any reason you took the grounding wire off the water pipe and you were touching the copper pipe, you become the path to ground and your wife is a rich women. Please picture this in your mind, you have the ground wire in your dominant hand and you are in all likelihood going to to touch the pipe with your opposite leg or that part of your body; where does the path of electricity decide to go, it goes from right to left or left to right depending on your dominant hand and quess what is is in the direct path , YOUR HEART, can anyone say funeral home? I was reading on the internet, that they have at the least, two occasions, that electricians have been killed because of this anomaly. So much for the education we received at trade school. So be careful and have a Happy Easter, I hope the weather is warmer in your locality. All the best Jack

JUGHNE

My best guess is that the power company has bad connections on their primary side ground/neutral. Could be some distance away. IMO they should be informed that you are getting stray voltage with your power disconnected at the house.

jumper

One amp is a lot. Where can it be going?

Zman

@Jackmartin

Thanks for the story. I think you and your son's assessment is absolutely correct.

I warn people about the hazards of working around water line bonds all the time. I think every plumber I have told thinks I am crazy. Only old crusty electricians get it, they just smile and nod.

AnthraciteEnergetics

This was happening at my house except it was more like 5 amps. Water mains are metal, and most of the homes have a copper service line and the neutral bonded to the service line. It's current from the neighbors homes finding its way back to the source through the water mains and ground.

The voltage between the pipe and neutral bus in my panel was low, maybe 0.25 V, but the impedance of a 3/4 copper pipe and iron water mains is so low that little voltage drives a lot of amps.

Disconnect it and bond to a second ground rod outside. Current through the water service line can accelerate corrosion.

EBEBRATT-Ed

Several possibilities. I have had this happen.

Since you had current flowing with the power to your sons panel shut off most of the power is coming from a neighbors house.

Most likely an open, loose or corroded neutral. If the connections are good you should have no current on the water pipe/grounding electrode conductor. The fact that the amperage went down when you shut off your sons panel means his neutral connections should be checked as well.

Current traveling through the earth has high resistance to go through to get back to the transformer. Electricity takes the path of least resistance. It won't go through earth if the neutrals are tight.

HomerJSmith

The NEC requires a #6 cold water ground within 6' of the panel as, I remember, to the meter panel (service entrance) grounding buss. A separate grounding electrode is also required.

I don't trust the clamp meter's reading, I would want to put a meter between the pipe in series with the grounding wire with the power to the house shut off.

I assume it is a 3 wire service to the house.

Leonard

I have similar current going down my city copper water pipe from the utility neutral. Possible it's a dangerous bad neutral connection in your neighbor's house , BUT typically It's because your neighbors ALSO have bonds from utility neutral to water pipe.

Basically water pipe is in PARALLEL with utility neutral, and so are your neighbors pipes. When your neighbors draw unbalance current from their 2 utility hots the current that you'ld expect to go down their utility neutral divides up among the parallel paths back to pole transformer based on resistance. If you opened the connection to pipe you'ld likely only see the IR drop of the utility neutral ( ~ 1 volt) IF all houses had good utility neutral connections back to street transformer.

However if someone had a bad or open connection you might see ~120 volts when you open the pipe connection. So good idea to first jumper the pipe connections your opening, for your safety.

EBEBRATT-Ed

@Leonard is correct but the earth has a high resistance and no current should pass to the water pipe if the neutrals are connected properly.

@HomerJSmith , the size of the grounding electrode conductor is based on the services over currant protection size. Minimum is #8 for 100 amp and #6 for 200 amp. there are other restrictions that may change that size

There is no distance given from the panel to any grounding electrode. A metal water pipe is used if available. Newer installations and upgrades for the past 35 years or so require 1 or 2 additional ground rods installed at least 6' apart. 2 ground rods negates ground rod testing

Mark Eatherton

What about the Ufer ground? When I was a young apprenti, I was cutting a tee into a 3/4" lead water service, and as soon as I cut the line, I could feel electricity pulsing through my body. I told my brother to go in the house and turn off the main breaker. The lady of the house wanted to argue with my brother telling him that we didn't need to get in the house, so he barged past her, shut the power off and came back out to check on me. I felt exactly when he shut off the power... A set of jumper cables would have been an excellent idea at that point...

Just when you think you've seen it all, Ma Nature jumps up and shows you something new

Work safely out there, or become a daisy pusher.

ME

Leonard

Some current can go thru the earth to end up back at the transformer neutral. (typically much much less than that going thru the pipe, maybe ~ 0.040 amp)

But that was not my point. My point was the water pipe connects all houses in a neighborhood, and all those houses connect that pipe to the utility neutral. And return current (neutral current) from each house splits between the utility neutral and the water pipe to get back to the utlity transformer neutral.

Depending current draw , some of your current goes into your water pipe to your neighbors pipe and back to transformer neutral thru THEIR utility neutral. Which way the current goes depends on the net neutral return current each house "makes". (and which utility hot the net current comes from)

clammy

I ran into this just a few weeks ago on a potable water line upgrade where the town required a increase in water main and water lines in the home being a new bath was being installed and inspector stuck to his guns .As my buddy was disconnecting the water meter he had sparks and the whole house lights dimed .I quickly advised him to reconnect and we advised the GC who contacted a lic electrician .Found there was no neutral from ulitilty pole and no grounding rod connected to panel .the panel had a passed inspection sticker .It was a lucky find only because of a hard inspector who is now enforcing a old code on water service and sizing espically where baths are being added to existing homes making services and hot and cold mains to be upgraded to 1 inch.In my area theres been alot more of this going on but in one town its just about every job ,good for u$ but bad for the HO and GC s who don t fiqure for it or except us to get some way around it lol can never make this stuff up .Just have to always remenber to keep on your toes have a meter and when it comes to electric chk it yourself with a real meter .Peace and good luck clammy

EBEBRATT-Ed

@Mark Eatherton Ufer is a lot better ground than a water pipe.

@Leonard , I don't agree about the current splitting. No current in a correctly wired job should go back through the water pipe ground. If it did that regularly all our house would be charred foundations.

In reality it will happen if the house has an open neutral. If you still have current flowing through the ground wire when the power to the house is shut down then your neighbor has a bad neutral and is causing current flow through your water pipe.

So even when you power is shut off your neighbor can burn your house down

Leonard

I agree that no current is intended to go down the water pipe. But when you have parelle paths for electricity you can not stop that from happening.

The IR voltage drop (normally maybe ~ 1 V max) along the intended utility neutral overhead wires back to transformer causes a current to flow thru ANY parelle path ( the water pipe to your neighbors utility neutral, and eventually back the source transformer's neutral terminal )

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"So even when your power is shut off your neighbor can burn your house down" .... YES I agree. Can also cause fire in your house if you lose the neutral and are using lot of net amps from one of your utility hots (unbalance amps).

Been thinking about upsizing my wire from breaker panel to water pipe to protect against this. Think NEC code only specs out a min wire size for that, not a max size. I've seen it very large in a 400 amp 3 phase restaurant service, maybe as large as the utility hots. (Ironically the wire had larger cross section than copper of the pipe, , guess they figure pipe is "water cooled")