Neutral current on a metal plumbing piping system

[Jpflex]

Your example of a neutral touching a metal box is an example of objectionable current. Current on a metal underground water pipe is a byproduct of a properly bonded electrical system.

Thanks for confirmation Dave

 

[winnie]

Your example of a neutral touching a metal box is an example of objectionable current. Current on a metal underground water pipe is a byproduct of a properly bonded electrical system.

IMHO this distinction is only true because of the different 'jurisdictions' involved. Inside each separate building the NEC gets applied separately. Between buildings the power company rules apply. This results in a legal requirement for multiple connections between the electrical system neutral and the grounded metal water pipes.

If the entire electrical system starting at the utility transformer were under the NEC, then this would all be 'objectionable current'. If this were all under the NEC, then 'service drops' would have a separate neutral and EGC, and the bond would happen at the transformer only. But these are not the rules that govern the entire system.

-Jon

 

[ActionDave]

IMHO this distinction is only true because of the different 'jurisdictions' involved. Inside each separate building the NEC gets applied separately. Between buildings the power company rules apply. This results in a legal requirement for multiple connections between the electrical system neutral and the grounded metal water pipes.

If the entire electrical system starting at the utility transformer were under the NEC, then this would all be 'objectionable current'. If this were all under the NEC, then 'service drops' would have a separate neutral and EGC, and the bond would happen at the transformer only. But these are not the rules that govern the entire system.

-Jon

I agree. That's why I have named it the Unavoidable Objectional Current.

 

[Fred B]

possible in a fluky or sketchy situation. Say, if someone deliberately used the pipe as neutral return, i.e. some awful DIY hack job that was completely unsafe but 'worked' at the outlet. Or some crazy fluke involving a combination of multiple errors and/or accident.

Seen it. Clamped on my fox & hound on the neutral and hot to trace a circuit, and the water line was ringing in. Fortunately this was during the process of a rewire anyway, so when the circuit was ultimately replaced the ringing waterline was gone. All blind fishing so some of the damage was not revealed so not sure of the exact contact point to cause the ringing waterline but it was ringing louder than the circuit wire so the trace was not easy.

 

[Bro8898]

The neutral is a 'grounded conductor', meaning that even with current flowing it is maintained at near soil voltage. The voltage between this neutral and soil is low, so if you touch both it doesn't shock you.

Thank you for the response.

Are you saying that the neutral can have a high amount of current on it but a low amount of voltage?
If you touch a hot wire it will shock you though right? What if you somehow grabbed a bare hot in an unbroken place on the wire? There would be no difference in potential because there aren’t two broken ends with current running between them. But is the difference between the earth and the voltage on the wire? As opposed to a neutral wire with no difference in potential to the earth?

 

[winnie]

Keeping in mind that I was trying to keep things simple, you understand what I was saying correctly.

The intact neutral can have high current with low voltage to 'earth'. Touching an intact neutral while in contact with other 'grounded' material usually has little shock risk. (Note: there are rare cases where the neutral can have enough voltage to cause problems.)

If you were to somehow grab an unbroken hot wire yet yet touch nothing else, you wouldn't get shocked. Think bird standing on a wire. The hot wire has high voltage to earth even with no current flowing and is a shock hazard.

Jon

 

[Bro8898]

Keeping in mind that I was trying to keep things simple, you understand what I was saying correctly.

The intact neutral can have high current with low voltage to 'earth'. Touching an intact neutral while in contact with other 'grounded' material usually has little shock risk. (Note: there are rare cases where the neutral can have enough voltage to cause problems.)

If you were to somehow grab an unbroken hot wire yet yet touch nothing else, you wouldn't get shocked. Think bird standing on a wire. The hot wire has high voltage to earth even with no current flowing and is a shock hazard.

Jon

Thank you. Very interesting. How cool. So the neutral has a low voltage to earth but the hot has a high voltage to earth? So this is also why generally you don’t get shocked when you touch the electrode grounding conductor that attaches to the ground rod right? I know it’s bonded to the same place in the box that the plumbing water pipe is. If you were to touch a service neutral with current flowing back to the transformer on it would you be shocked, like if you opened up the box and touched that one big aluminum wire only?

I’m starting to understand that if you were to somehow touch a pipe with current and also something else that’s bonded to ground like the electrode grounding conductor you would get shocked. I think.

Thanks again for the info

 

[kwired]

You can use a set of automotive jumper cables; split them to make two jumpers.

just don't buy some the cheap ones out there that have terrible clamping methods. Keep in mind many out there probably don't work so well on 1 inch and larger pipe size either unless you have some fitting in the system that is easier to clamp to.

 

[kwired]

Thank you. Very interesting. How cool. So the neutral has a low voltage to earth but the hot has a high voltage to earth? So this is also why generally you don’t get shocked when you touch the electrode grounding conductor that attaches to the ground rod right? I know it’s bonded to the same place in the box that the plumbing water pipe is. If you were to touch a service neutral with current flowing back to the transformer on it would you be shocked, like if you opened up the box and touched that one big aluminum wire only?

I’m starting to understand that if you were to somehow touch a pipe with current and also something else that’s bonded to ground like the electrode grounding conductor you would get shocked. I think.

Thanks again for the info

Ohm's and Kirchoff's laws are at play here.

The grounded conductor is grounded because it is referenced to earth, on a utility derived system it is referenced many times - like at nearly every structure in the distribution system as well as at each individual service.

That multi-grounded conductor does have voltage drop across segments of it, all conductors have a voltage drop across them if current is flowing. This drop is usually minimal but in right conditions even just 2 or 3 volts can be enough to shock you. That risk is about as high as it gets for us humans in situations involving swimming pools or other situations where you may be immersed in a body of water and is reason there is extra bonding requirements for some those kinds of applications.

Also misunderstanding is the myth that electricity takes the path of least resistance. Electrical current takes all possible paths, but the path with the least resistance does take the majority of said current. Even with a bonding jumper across the section of pipe you are working on, you possibly have a small current pass through you if you touch the work, but the resistance of the bonding jumper is so low in comparison to you and carries such a high percentage of the total current resulting in current passing through you being so low it is not enough to cause any concern for you. Add some kind of resistance to that bonding jumper and current passing through you rises, add enough resistance and you eventually get enough current passing through you that you can feel it.

 

[don_resqcapt19]

Thank you for the response.

Are you saying that the neutral can have a high amount of current on it but a low amount of voltage?
If you touch a hot wire it will shock you though right? What if you somehow grabbed a bare hot in an unbroken place on the wire? There would be no difference in potential because there aren’t two broken ends with current running between them. But is the difference between the earth and the voltage on the wire? As opposed to a neutral wire with no difference in potential to the earth?

The only voltage to earth on a neutral of a grounded system, is the voltage created by the voltage drop on the neutral conductor...typically not more than a few volts, and not a shock hazard.

For an analogy to your trade, voltage drop is the equivalent of friction loss. In both cases the loss increases with increased volume. Volume being flow rate or current as the case may be.

 

[SceneryDriver]

The bonding jumper with the pipe clamps is a good idea to keep you safe while working.

Do remember, however, that if you have a situation where you have current on the water line, and you install fitting(s) that are non-conductive, you have broken the neutral path. This means that removing the ground clamp setup can lead to you getting shocked. With the neutral for the building now unconnected, it may also lead to damage to customers' electrical devices due to a lost neutral.


SceneryDriver