Bonding and Grounding Copper Pipes

[Bro8898]

Hey guys. I’m new here. I’m a master plumber from bham al and looking for some advice on metal water pipes. I’ve searched plumbing forums high and low for answers and cannot find what I’m looking for. Any advice would be greatly appreciated.

I understand a little about the difference between grounding and bonding and have watched many of Mike’s videos on it. You can give explanations of it as they apply but I have a practical question from a plumbing standpoint that I would like some feedback on.

At what point does it become dangerous to disconnect a metal water pipe? Not only dangerous as far as me getting shocked but dangerous as far as frying all the appliances in a house. Fortunately that hasn’t happened to me (yet) but I’ve heard stories about it. I want to know as much as I can to avoid this situation at all costs. Not only for my safety but for the safety of the occupants as well avoiding destroying any of their appliances.

I know there is a ground/bond wire where the pipe enters the house. What I’ve seen on jobs is when you’re working on the “yard” side of the wire you need some sort of jumper until you replace the copper pipe you removed to work on (in order to maintain the bond or continuity or whatever) and then the jumper can be removed. On the “house” side of the ground wire it seems safe to disconnect pipes and replace with plastic (pex) if necessary. But I’ve also heard horror stories of plumbers disconnecting water heaters and electricity arcing and frying all the appliances in the house. They said something about the “utility neutral” being lost and the house becoming the neutral and when the pipes get disconnected the plumber becomes part of the path if he is touching each end of the pipe that has just been broken.

Sorry for the long explanation and question. Again any help and advice would be very much appreciated. So here’s the question one more time:

At what point does it become dangerous to disconnect a metal water pipe? And if a section of metal pipe is cut out and replaced with plastic (pex), when will I be breaking the continuity and putting safety of the occupants and appliances at risk? This applies to both the “yard” side and the “house” side of the ground/bond wire.

Thanks in advance

 

[don_resqcapt19]

It is almost impossible to know when it will be dangerous.

Where there is a common metal underground water piping system, the service can lose it neutral and there will be no symptoms. The metal water pipe, as a result of required bonding at each building, will serve as the neutral and the building occupants will not have any idea that there is an electrical problem.

Opening the water pipe under that condition poses the risk of both "frying" equipment in the building and a serious shock hazard for the person cutting the pipe or removing a fitting>
I am pretty sure Mike has some videos on the effects of an open neutral. I think they are mostly about an open neutral on a branch circuit, but the same thing occurs where the service neutral is open, with even worse results because more equipment is exposed to the high and low voltages that result from an open neutral.

There should be no risk where you replace a section of the interior piping, assuming the bonding connection is at the water pipe entrance to the building as required by the code. If you are only replacing a small part of the interior metal piping, then a bonding jumper should be installed around the non-metallic section. Note there there could be some rare cases where there is a risk to you and building equipment when cutting an interior metal water pipe, but they would involve existing code violations.

Assuming that the service neutral is intact, there is no issue with replacing the outside water piping with nonmetallic. The code requires that where the metal underground metal water piping is used as a grounding electrode, that it be suplemented with an additional grounding electrode.

 

[Dennis Alwon]

Complicated question.

I always tell plumbers to use a jumper cable between the sections of pipe where you are going to cut the plumbing. There should not be a large amount of current on the plumbing line but there certainly can be.

Today plumbing pex or whatever is used breaks up most of the copper lines so in those cases it is not an issue. If there is copper lines coming in from outside with 10' or more in the earth then that copper pipe should be hooked up to a grounding electrode conductor.

The biggest issue is when you have community water and there is no dielectric fitting to separate the copper in the earth from the plumbing in the house. You could get current or at least voltage from house nearby. I have never seen a plumber mend the integrity of a metal plumbing system but you could run a grounding electrode conductor between the piece of pipe that were replaced.

 

[mikeames]

There's a lot to unpack here.

1. No current should be on metal waterpipe under normal ideal conditions, and very little in reality. If a utility neutral is compromised then it will start to carry current. If its totally lost its possible for it to all be on the water pipe back-feeding through other house services.

2. Water pipes (metal) in the past were dominantly used as the grounding electrode, now because of plastic concrete encased electrodes and ground rods as supplements are used more and more.

3. Grounding is a connection to earth, bonding is connecting things together. So the connection that ties the service neutral to the water pipe is the bond but the waterpipe or Grounding Electrode is the ground. When you bond something to the grounding electrode you are grounding it.

4. Generally if the water pipe is used as a grounding electrode, then the grounding electrode conductor will bond to it within 5 feet of point of entrance of the house to minimize the chance that the plumbing be disconnected and compromise the integrity. This is why you will see a grounding electrode conductor jumper around the water meter.

Perhaps the only way to tell how much current is on a pipe is to put an amp meter around it. If there is no current then you wont hurt anything if its disconnected. If there is current on it then its possible, but its because of a more serious failure or compromise on the service neutral.

Disclaimer- 2 others just replied while I typed this.

 

[winnie]

Electricity is always seeking a path back to its source. Not to 'ground', not to the 'Earth', but back to its source. Generally the local 'source' of electricity is the local utility transformer.

For various safety reasons, most electrical services are 'grounded', meaning that the electrical system is intentionally connected to soil, and making things like soil or metal underground piping a potential path back to the source of electricity.

In the situation that OP describes, one of the utility conductors has failed. This utility conductor is the 'grounded' conductor, commonly the 'neutral'. But because of the grounding connection to common metal underground piping, this failure is masked by current flowing back to the source via the piping.

Break the piping, and now there is no good path back to the source. You can see high voltage, arcing, or equipment damage.

A full evaluation to determine that there is no danger would require an electrician working at the main electrical service to determine if there is neutral defect or neutral current returning via underground piping.

A partial evaluation could reasonably be run by a plumber, simply using a large enough clamp on current meter on the pipe being cut. No current means very low risk. Not zero, because the measurements might be made when the current is low for other reasons.

Also, if current is measured on the water piping, the problem may not be with the building being services, but with a neighbor building, where current is returning via the intact neutral of the building in question.

-Jon

 

[hbiss]

If the house or building is served by a metallic water service line which connects to a metallic water main, the service lines and the mains are essentially electrically in parallel with the utility neutral conductor that runs from pole to pole and into each house. This is because at each house there is that ground/bond wire that connects the utility neutral through the electric service to the water service line. It's a big network. So, not only does neutral current flow through the utility neutral, it also flows through the water lines. It also means that because the whole neighborhood is electrically interconnected by both the water system and utility, there is no telling how much current there may be flowing from the utility out at the pole, through a particular service drop, through that ground/bond and back to the water system- or from the water system back to the utility.

Now, in the instance where a house has lost it's neutral utility connection the water system will take it's place which can result in additional current on the water service and ground/bond. And that's the case where, if you interrupt the water service line or remove the ground/bond wire, electrical equipment in the house can be damaged because now there is nothing. Thing is, if that situation does occur I can't see it as being your fault or what you could have done about it. You are a plumber, not an electrician. Just don't disconnect a water service line and grab both ends at the same time! The suggestion to use a jumper cable is a good one.

Keep in mind also that the instances of a completely metallic water system are few these days with service lines, additions and repairs made with PEX. Unfortunately in those instances where a house loses the neutral there is no "backup" and things get fried.

Consider houses on their own (well) system.

-Hal

 

[don_resqcapt19]

There's a lot to unpack here.

1. No current should be on metal waterpipe under normal ideal conditions, and very little in reality. If a utility neutral is compromised then it will start to carry current. If its totally lost its possible for it to all be on the water pipe back-feeding through other house services.
...

With a common metal underground water piping system in the area it is common to find 20% or even more of the neutral current on the water line, even where the service neutral is in perfect condition.

 

[drcampbell]

... Perhaps the only way to tell how much current is on a pipe is to put an amp meter around it. If there is no current then you wont hurt anything if its disconnected. If there is current on it then its possible, but its because of a more serious failure or compromise on the service neutral. ...

Even a direct measurement is of limited value. There might be no current at the moment you measure it, but that could change when something turns on.

 

[mikeames]

With a common metal underground water piping system in the area it is common to find 20% or even more of the neutral current on the water line, even where the service neutral is in perfect condition.

I can certainly understand the how, but I have never seen it. That don't mean squat though.

 

[don_resqcapt19]

I can certainly understand the how, but I have never seen it. That don't mean squat though.

A few months ago we has storms that took out a lot of trees. A few houses down from me a large branch fell on a service drop and broke the service neutral. The ungrounded conductors remained intact. There were no power issues in the house, and that house ran using the water pipe neutral for about 3 days before the utility got to them. I think that they were not even on the list because smart meter had not reported loss of power.

This is pretty much something that only happens in older areas and even there, water main replacement is almost always done with nonmetallic piping. But in the areas with metal lines (last year was the first time our city permitted anything other than copper as the service to a house) to the buildings and cast iron mains have a portion of the neutral current on the water line, and often, as in the case above, the building can function just fine without the service neutral.

 

[LarryFine]

For there to be an appreciable voltage across an opened connection, there must be current through it while it's closed.

The simplest check would be to test for current on the pipe with a clamp-on ammeter.

 

[don_resqcapt19]

For there to be an appreciable voltage across an opened connection, there must be current through it while it's closed.

The simplest check would be to test for current on the pipe with a clamp-on ammeter.

But if the service neutral is intact, there will be little voltage even though there is current. With the water pipe and the service neutral in parallel, the only voltage across an open on either one would be the voltage drop on the other.

If there is no current, it is likely to be safe to cut the pipe, but even where there is current, it still may be safe to cut the pipe. There is no way to know if the current on the water pipe is a problem without also checking for current on the service neutral. If there is current on both, with more on the service neutral, it is likely to be safe to cut the pipe.

 

[Bro8898]

Wow. Thank you all for the informative replies. That was more in one day than I’ve learned in years. Based on your responses and to keep things simple how does this sound???

When working on the “yard” side of the wire attached to the pipe (the side in contact with the earth that should be within 5 ft of entering the house) it sounds like a good idea to put a jumper on while disconnecting the pipes and then replace the existing damaged metallic pipe with new metallic piping (for a repair situation).

But on the “house” side of the wire (the side coming in the house after where the wire is attached) it would be a good idea to clamp an amp meter around the pipe to see if there’s any current on it. If not it’s safe to disconnect and replace with pex. If there is current on it I guess I would put a jumper on it and replace with metallic piping.

In both situations I would plan to remove the jumper after completing the repair (because in that case I would just go ahead and replace existing metallic piping with new metallic piping). In the situation that I can use pex and there’s no current on the pipe then I would guess there’s no reason to install a jumper.

Is this what you all would do?

Again thank you everyone for your informative responses. Can’t tell you how much I appreciate your thoughts and effort in answering.

 

[LarryFine]

When working on the “yard” side of the wire attached to the pipe (the side in contact with the earth that should be within 5 ft of entering the house) it sounds like a good idea to put a jumper on while disconnecting the pipes and then replace the existing damaged metallic pipe with new metallic piping (for a repair situation).

But on the “house” side of the wire (the side coming in the house after where the wire is attached) it would be a good idea to clamp an amp meter around the pipe to see if there’s any current on it. If not it’s safe to disconnect and replace with pex. If there is current on it I guess I would put a jumper on it and replace with metallic piping.

I'm suggesting checking for current on whichever section of pipe you intend to open.

Any current seen there should match any seen on the service grounding wire.

 

[Bro8898]

Maybe the easiest way to say it is:

What would you do if it were you?

 

[Bro8898]

I'm suggesting checking for current on whichever section of pipe you intend to open.

Any current seen there should match any seen on the service grounding wire.

Thank you

 

[roger]

Bro, here is an illustration that shows current flowing through a group of houses when a metallic underground service is used and one house has an open neutral. The metallic piping is now carrying the current and cutting it anywhere in the group would be dangerous. Bridging the cut with your body would cause you to become a conductor for the current flowing.



Roger

 

[Bro8898]

Bro, here is an illustration that shows current flowing through a group of houses when a metallic underground service is used and one house has an open neutral. The metallic piping is now carrying the current and cutting it anywhere in the group would be dangerous. Bridging the cut with your body would cause you to become a conductor for the current flowing.

View attachment 2554697

Roger

Thanks Roger. That’s very helpful. Like a former poster said, there’s no way to know whether there’s an open neutral somewhere (at least not for me with the limited knowledge I have). So even if a pipe has current on it I can still touch it and not get shocked, right? It’s only when I open up the pipe and touch both sides that I become a part of the conductor and can get shocked (or damage electrical appliances), right? So the safest way to proceed is to clamp an amp meter around the pipe before breaking it and if it has current on it then I know there’s a fault somewhere. What kind of reading am I looking for if I do this?

Thanks

 

[Bro8898]

Interesting I just read this after googling current on a water pipe, which I think another poster made a point about:

• An open neutral in the electrical service line to the building will often result in very high, and highly variable, current on the water service line. This is universally recognized as a serious safety problem among electric utilities and electricians. It is very importantto note that the absence of any current measured on a water line does not confirm that an open neutral condition DOES NOT exist. There may simply be no loads operating in the building. Also, a measurement of many amps of current on the water line does not indicate that an open neutral condition DOES exist. Only structured testing under controlled load conditions will permit this determination. A major implication of this is that a plumbing contractor cannot use a simple current measurement as a singular indication that it is safe to cut into a pipe. A voltage of 120 Volts or more could appear across the two ends of a cut pipe without warning. With wet hands on a copper pipe, this could be a fatal mistake.
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  So what am I to do?!?!
  
  
  
  
  
  

 

[winnie]

As I stated above, an open neutral situation can only be confirmed by taking measurements in the main service, requiring the services of an electrician.

Measuring current on the pipe you are cutting will give you a good idea of if there is a problem present, but cannot give a guaranteed result because as noted a low current might be the result of low neutral load.

IMHO what you should do as a plumber is to have a good set of bonding jumpers which you use to bypass any section of metallic service pipe which you may be cutting, and use those bonding jumpers religiously. Use something which can't be knocked off by accident.

Also, if you measure high current (several amps) on a pipe that you are about to cut, you might request the customer bring in an electrician.