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Melted Ground


Jerry Simon
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I'm the guy who always checks water piping with my clamp ammeter, and find a few amperes of current in the pipe coming from the panel ground wire (those homes with metal muicipal supply pipe).

Here's today's pic...this is the water meter ground jumper cable. It literally "fried" right off of the pipe clamp.

No current currently in pipe. Any thoughts on why this may have occured. NOte: vacant house, and neighbor volunteered to my Client that prior owners had been having some electrical problems.

Thanks!

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On my monitor it looks more like corrosion than burning.

BTW, in response to your past findings, I've been clamping ground wires every now & then for the past year or so(has it been that long?)

I almost never find anything though occasionally the strangest thing happens. My meter would show a small reading but it would come & go. After puzzling over it for a while I realized that it had to do with the physical orientation of the meter. Have you ever had that happen or should I just start shopping for another meter?

- Jim Katen, Oregon

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This wire over-heated...wasn't from corrosion. If you look closely at the end of the white wire insulation (may be hard to see well), it turned very brown from the heat, just like you'd see the end of a neutral wire turn brown at a bus bar connection that over-heated from sharing two hots on the same phase. In person, it is very obvious this was from heat.

Lightning? Don't know. This was the only thing with damage...nothing in the panelboard like I'd expect from lightning.

Again, neighbor said Sparkys have been to the home before 'cause of "problems"...don't know the nature of the "problems"...vacant house, neighbors hearsay.

Jim...I posted on ASHI about a year ago about current bleeding from ground to water pipe. I even posted a picture of my ammeter with a record finding of 23 amperes in the pipe! Have also seen current run into gas pipe that was lying on the water pipe. From the ground?...Yes...I disconnect the ground, current in pipe disappears.

Some local utility guy said the older utility co. infrastructure is undersized for the tear-downs(very common around CHi-Town) and resulting service size increases in the new, bigger homes...the utility co. older neutral is undersized, and can't handle all (increased) return current...thus, it bleeds to ground & into house water pipe.

Would love to hear Dougs thoughts.

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Originally posted by Rob Amaral

BTW, have any of you had experience with 'how far into the ground' this type of damage on the pipe can go?

Yes, here in central FL, lightning capital of the US, it's been known to cause pinhole leaks in the copper far removed from the connection of the grounding wire.

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Mike: I have no way of knowing how deep the pipe is wrapped. I advised them to have the town shut off the water at the curb valve, remove the meter, examine the pipe more closely and try to determine the 'depth' of the damage. Very brittle pipe. Thanks for the FL response. FL is indeed the lightning capital of the US. I'll pass that along.

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Originally posted by Douglas Hansen

The readings that you get confound my knowledge of electrical systems. I don't have a good answer.

I find current on the GEC on a regular basis and I can explain it. It's really quite simple. This occurs in neighborhoods where the water lines are all metal. In this case, every electrical system in every house is connected together. When resistance in the neutral goes up, some of the current flows over the GEC, to the metal water piping, to your neighbors house, over their GEC, to their neutral, and then back to the transformer. Or vice versa. Your neighbor can have a bad neutral connection that puts current on your water piping.

It’s really quite common in older neighborhoods.

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Hello Douglas:

In your response, and I’m paraphrasing, you stated:

Sure, the grounding electrode conductor is in parallel with the neutral, and is theoretically capable of carrying some current. However, simple Ohm's law calculations tell us that the amount of current should be negligible. If the resistance of the service neutral is relatively high, say .5 ohms, and the resistance in the earth is relatively low, say 20 ohms, we should still have 100 times as much current in the neutral. Add to that the fact that the current in the neutral should only be the imbalanced load difference between the two hot conductors, and I'm completely at a loss to explain some of the extraordinarily high readings you are getting. Let's try some examples in my theoretical 20 ohms and .5 ohms scenario:

You said that the service neutral is relatively high at .5 ohms and that the resistance in the earth is relatively low at 20 ohms.

Are these two numbers reversed? .5 ohms is less resistance than 20 ohms or am I missing something in your explanation?

Thanks!

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Mark Cramer...you make good sense...it is VERY common, and this "stray" earth current is ONE explanation. However, on more than a few occasions, I (& Seller's electrician in one instance), noted the current, then disconnected the panel ground, and voila!...no more current to the water pipe. None,..zippola. But like you say, other times current remains, so must be coming from the earth.

Doug...I too apologize for the other board comments, though I don't remember them. But knowing me, I most certainly contributed to the lack of humor. By the by, I use a SPERRY Model DSA 600 (digital readout).... & thanks for your input.

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Hi,

Most new construction around here the below grade pipe is wrapped with the equivalent of a wide black plastic electrical tape and padded like that with foam only where it passes through the concrete. Sometimes though, the foam goes farther. I though, given the frost depth in MA, that you guys there might wrap it further.

ONE TEAM - ONE FIGHT!!!

Mike

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Originally posted by Jerry Simon

Mark Cramer...you make good sense...it is VERY common, and this "stray" earth current is ONE explanation. However, on more than a few occasions, I (& Seller's electrician in one instance), noted the current, then disconnected the panel ground, and voila!...no more current to the water pipe. None,..zippola. But like you say, other times current remains, so must be coming from the earth.

It's not stray current coming from the earth. It's coming from a neighbor's service, over the common water piping in the neighborhood through your service, back to the transformer, where it originated. If they have a neutral connection with high resistance, some of their current will flow back to the transformer over your neutral.

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Originally posted by Jerry Simon

Mark...where does the stray current come from that's in the earth that shocks farmers cows?...seriously. And, sorry I mis-read your post and that I ASSumed you meant such earth stray current.

There's always some current flowing through the earth, because the entire electrical grid is grounded. Some of the current always flows through the earth back to it's point of origin. But those currents are usually in the milliamp range, not amps like we see on water piping. Here's an article that talks about that: http://www.mikeholt.com/documents/stray ... rrents.doc

There are also cases where the neutrals on the utility companies underground cables are deteriorating and allow higher levels of current to flow through the earth.

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