Grounded conductor (neutral) and earth voltage

Thank you so much Jonathan. You have been a blessing. Along with the other members of the forum. I can’t tell you how much I appreciate the time and thought you put into informing me and teaching me. I feel much more confident although it took years to gain some of these basic concepts. I’ll give you my word I will use this information for good purposes.

If you ever have any plumbing questions or need any code references I feel like I can help you in that area. And hopefully return the favor somehow. I am sincerely grateful for your teaching and guidance.
 
winnie said:
Yes. A bad open neutral without a metallic alternative path would make it self quite apparent to the homeowner.



Yes. I recall when we last discussed this topic, we suggested having suitable jumper cables available when you were cutting pipes where this was a risk.

-Jonathan
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Hey Jonathan. I have one more question. If I put an amp clamp around a pipe to determine if there is a serious amount of current on it before opening it up, how many amps would I be looking for?

I know it varies but how much would be considered an indicator that an unsafe amount of neutral current is flowing on the pipe?

Thanks
 
Bro8898 said:
Hey Jonathan. I have one more question. If I put an amp clamp around a pipe to determine if there is a serious amount of current on it before opening it up, how many amps would I be looking for?

I know it varies but how much would be considered an indicator that an unsafe amount of neutral current is flowing on the pipe?

Thanks
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Any current large enough to be detected by a clamp on amp meter means you have a potentially lethal voltage difference between the two ends of the pipe once you cut or disconnect.
 
retirede said:
Any current large enough to be detected by a clamp on amp meter means you have a potentially lethal voltage difference between the two ends of the pipe once you cut or disconnect.
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Correct, 30mA can be fatal so if your clamp on is seeing even a 1/2A watch out. This is why proper bonding so necessary, if that level of potential is present likely due to a fault condition proper bonding should produce a response from a properly operating system to eliminate by breaking the power source to the fault.
If the source for the high potential on a piece of water pipe is an "open" or weak neutral back to the source, it is usually indicative of the systems grounding is a higher resistance that the water pipe is presenting and allowing a higher percentage of the return to the source to use a non-electrical system metal as the return path. The current present can widely be variable from 0 to ? (depending on system voltages) and depending on the load imbalance present on the L-N. Seen it fluctuate L1,N-L2,N from as little as a couple of volt to as much as 60 or 70 volts. L1 60V L2 180V. And the difference if given a lower impedance path it will use that as first choice return (higher percentage of the current) and if that is You and the plumbing watch out.
 
Fred B said:
Correct, 30mA can be fatal so if your clamp on is seeing even a 1/2A watch out. This is why proper bonding so necessary, if that level of potential is present likely due to a fault condition proper bonding should produce a response from a properly operating system to eliminate by breaking the power source to the fault.
If the source for the high potential on a piece of water pipe is an "open" or weak neutral back to the source, it is usually indicative of the systems grounding is a higher resistance that the water pipe is presenting and allowing a higher percentage of the return to the source to use a non-electrical system metal as the return path. The current present can widely be variable from 0 to ? (depending on system voltages) and depending on the load imbalance present on the L-N. Seen it fluctuate L1,N-L2,N from as little as a couple of volt to as much as 60 or 70 volts. L1 60V L2 180V. And the difference if given a lower impedance path it will use that as first choice return (higher percentage of the current) and if that is You and the plumbing watch out.
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Thank you for the detailed response. This is all good information for me. And especially important to understand that no current should be detected by a clamp on meter before working on a pipe.
 
This meter looks interesting for checking current on pipes prior to cutting them:
www.kleintools.com

Clamp Meter, Digital AC Electrical Tester with 18-Inch Flexible Clamp - CL150 | Klein Tools

This clamp meter is easy to use, stand-alone, and features an 18-Inch flexible clamp that allows access into panels and hard to reach areas (bundled wires, awkward conductors, and PLC cabinets). True RMS readings with CATIV 600V or CATIII 1000V safety rating. Features backlit LCD display...
www.kleintools.com www.kleintools.com

Does anyone have experience with this meter? Will it work well on steel conductors? The spec says it will measure down to 0.01A; is this realistic?

-Jonathan
 
winnie said:
There is one scenario that IMHO is quite plausible, especially for someone in a shower.

Metal supply pipes are pretty much universally bonded to the electrical system.

But I think people generally ignore drain pipes.

Lots of old houses have cast iron drain stacks leading to underground cast iron pipes, and these don't get bonded.

I could imagine someone standing in the shower, with their feet in water that is in contact with a grounded metal pipe, feeling a jolt from a metal shower head connected to an electrical system with a broken neutral.

-Jonathan
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Something I thought about in all this. Let’s say there is an open neutral and no return path so the all the current is flowing between the two 120v hot conductors. If I went to a plug outlet and measured between neutral and ground would I see a voltage potential? My guess is that there would be zero volts because both are still tied together at the main panel. But if I measured neutral or ground to a neutral that is in the circuit (ie an appliance is connected and turned on) then I would see a voltage difference. Also I would have a voltage difference between the two broken ends of the “open neutral”. Does all this sound correct?
 
It would depend where the neutral break is located.

If the panel has a proper ground to neutral bond, and the neutral break is on the utility side of things, then all the home neutrals and grounds are connected to the series circuit. You would have low neutral to ground pin voltage all over the house.
 
Bro8898 said:
Something I thought about in all this. Let’s say there is an open neutral and no return path so the all the current is flowing between the two 120v hot conductors. If I went to a plug outlet and measured between neutral and ground would I see a voltage potential? My guess is that there would be zero volts because both are still tied together at the main panel. But if I measured neutral or ground to a neutral that is in the circuit (ie an appliance is connected and turned on) then I would see a voltage difference. Also I would have a voltage difference between the two broken ends of the “open neutral”. Does all this sound correct?
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As Jon said if the open neutral is on the service and the main bonding is okay you would not see voltage there.

But if you have an open neutral on a feeder or branch circuit — to be precise, if the break is upstream of where you are measuring measuring to the neutral, but the EGC to the same point is okay — then you'd expect to see voltage between neutral and ground if any load is connected.
 
I got a call from a plumber friend last week, her pipe wrench sparked when it bumped a dryer in the laundry room, she was replacing a valve at a washer in a old building and got a very good tingle from it. Turns out the dryer was running and the old 3-wire had a loose noodle, not sure how it was still running. But those old 3-wire circuits are something to be aware of if you do service work.
 
winnie said:
It would depend where the neutral break is located.

If the panel has a proper ground to neutral bond, and the neutral break is on the utility side of things, then all the home neutrals and grounds are connected to the series circuit. You would have low neutral to ground pin voltage all over the house.
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Thanks. Yes the neutral break would be on the utility side. And neutral and ground are properly connected in the panel. When you say low neutral to ground voltage do you mean close to zero? It seems like since they’re both connected in the main panel that they’re both at the same potential.
 
jaggedben said:
As Jon said if the open neutral is on the service and the main bonding is okay you would not see voltage there.
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This is what I was thinking. I appreciate you confirming it. There seems to be no potential difference between them because there both connected in the main panel. But, there would be a potential voltage difference between any neutral/ground tied together in the main panel and the “open” side of the neutral leading back to the service right? Does that sound correct?
 
gene6 said:
I got a call from a plumber friend last week, her pipe wrench sparked when it bumped a dryer in the laundry room, she was replacing a valve at a washer in a old building and got a very good tingle from it. Turns out the dryer was running and the old 3-wire had a loose noodle, not sure how it was still running. But those old 3-wire circuits are something to be aware of if you do service work.
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Sounds like the pipe was grounded and the case of the dryer had some hot current on it and when the wrench touched between them current was able to flow. And a 3 wire dryer uses the same wire for ground and neutral so maybe there wasn’t a path of low enough impedance back to the breaker to trip the breaker. Or maybe there wasn’t enough current to trip the breaker. Maybe you can explain it better than how I’m trying to.
 
Bro8898 said:
This is what I was thinking. I appreciate you confirming it. There seems to be no potential difference between them because there both connected in the main panel.
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...

You asked about testing voltage between neutral and ground blades on a receptacle.
If there is any current flowing on the neutral, then there is theoretically a voltage difference, which will be equal to the voltage drop on the neutral between the receptacle and the main bonding jumper. In normally 120V circuits it's highly unlikely to amount to more than a volt or two even if it's a very long branch circuit. Jon was just being precise calling it "low" instead of zero. 'Negligible' might be more precise. For the situation where the neutral is open upstream of the main bonding jumper, it won't really be meaningfully different from what it is under normal load operation.
 
Bro8898 said:
Sounds like the pipe was grounded and the case of the dryer had some hot current on it and when the wrench touched between them current was able to flow. And a 3 wire dryer uses the same wire for ground and neutral so maybe there wasn’t a path of low enough impedance back to the breaker to trip the breaker. Or maybe there wasn’t enough current to trip the breaker. Maybe you can explain it better than how I’m trying to.
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Yeah the neutral on the dryer was loose, but the neutral lead of the 120V motor was bonded to the frame of the dryer, since the heating elements are 240V somehow the 120V dryer motor was able to run without a neutral. It was a mystery to me, perhaps one of the people smarter than me on here can explain it.
Years back my boss measured about 5 amps flowing on a gas pipe, it was a fancy combo gas / electric range on one of those special old 3-wire circuits and the neutral pin was broke off and stuck in the receptacle, so the neutral path for the range was via the gas pipe.
 
The Earth is basically a big battery. A bunch of chemicals in the soil with water. The earth potential is considered 0 but it reality it could be anything because it is only voltage in reference to another point.
 
jaggedben said:
For the situation where the neutral is open upstream of the main bonding jumper, it won't really be meaningfully different from what it is under normal load operation.
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This is what I was thinking. Thank you for confirming this. My main question in understanding all this was if was touching something grounded like a kitchen sink (because the plumbing pipe is bonded to the neutral bar) and I touched something else grounded like the case of a metal toaster that had three wires and was plugged in, and there is an open neutral condition where the service neutral is open as you described, then nothing would happen right? Because I’d be touching two things at the same potential, the open service neutral doesn’t change anything from normal conditions in this scenario.
 
Bro8898 said:
This is what I was thinking. Thank you for confirming this. My main question in understanding all this was if was touching something grounded like a kitchen sink (because the plumbing pipe is bonded to the neutral bar) and I touched something else grounded like the case of a metal toaster that had three wires and was plugged in, and there is an open neutral condition where the service neutral is open as you described, then nothing would happen right? Because I’d be touching two things at the same potential, the open service neutral doesn’t change anything from normal conditions in this scenario.
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Yes.
 
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