Current Measurement on Water Line

[Handy hank]

In acting as my daughter's agent following a home inspector check out a prospective home purchase, he measured 4.6 Amps on the main water line at the point where it entered the home. He wrote this up as needing an electrician to inspect. The electrician pooh-poohed the reading but did check things out and found a ground clamp on the gas line to be not to code.
I have been unable to find any reference to what a nominally acceptable level of current might be. The home inspector writes everything up if it exceeds 300 ma. This seems a bit low threshold. Are there any rules of thumb readings?

 

[don_resqcapt19]

I approved this thread as it is not asking for any DIY installation instructions. If it turns to that type of thread, it will be closed.

That being said, is there a common metal underground water piping system...that is one that may have connections to grounded conductors in othe buildings? Without know the current on the grounded conductor no one can say that the current the HI read is excessive. All grounding electrode systems provide a parallel path for grounded conductor current and the current will divide based on the impedances of the parallel paths.
It is not unusual to find 20% or more of the grounded conductor current flowing on the water pipe if the pipe is part of a common undergound system with connections to other buildings.

 

[tom baker]

If its served by a continuous metallic water line to the water main in the street, as Don says, this is not unexpected. The neutral current from this house is returning via the metallic water line to the source (transformer). The way to verify is to determine if the water service line is metallic, and then have water company pull the water meter (with insulating gloves). If the current goes away you have found the source.

The other possibility is a loose neutral at the service, meter or pole, again only an issue with a metallic water line.

The solution is to install a section of non-metallic pipe next to the meter. The AC current will not cause any corrosion on the water line.
The 300 mA number your home inspector came up with has no basis from the electrical code and I would like to know where he/she came up with it.

And on a related subject, if the report shows that you have GFCIs that don't work, thats because the home inspector does not know how to test them.

 

[templdl]

If its served by a continuous metallic water line to the water main in the street, as Don says, this is not unexpected. The neutral current from this house is returning via the metallic water line to the source (transformer). The way to verify is to determine if the water service line is metallic, and then have water company pull the water meter (with insulating gloves). If the current goes away you have found the source.

The other possibility is a loose neutral at the service, meter or pole, again only an issue with a metallic water line.

The solution is to install a section of non-metallic pipe next to the meter. The AC current will not cause any corrosion on the water line.
The 300 mA number your home inspector came up with has no basis from the electrical code and I would like to know where he/she came up with it.

And on a related subject, if the report shows that you have GFCIs that don't work, thats because the home inspector does not know how to test them.

I'm intregues with this 300ma came from also.
Also, it would be interesting to see which way the currect is flowing. There could be an outside chance that it could be originating from an outside source taking a path to ground through the SE panel's ground. It may not be a SE grounding issue at all.

 

[Handy hank]

Thank you to all that have replied so quickly.

To answer the questions posed, the house is a single family with a detached garage built about 12 years ago as a teardown/rebuild on the same foundation. As far as I'm aware at this time it has only one water line and one natural gas line coming into the house, both meters are outside. There is a power feed out to the garage but no water. It has a 200A service, no backup generator. It has a ground rod installed along with the water line and gas line ground paths all bonded to the service panel ground bus. The lot is rather small, with homes quite close on each side. The house has been purchased and they take occupancy in about 3 weeks. I can feel myself doing some additional measurements with different loading. One measurement I plan on is to measure the water line amperage when the main disconnect is off to see if there is any feedthrough from water utility and/or next door neighbors.

To add additional info, I attended the second contractor electrician's inspection ( a second opinion, as it were) of the grounding and watched his process for checking all the grounding/bonding. He only found a loose screw in the outside telephone's service entry box that was bonded to the GEC leading to the ground rod nearby. He also disconnected the GEC to the water line and looked for arcing initially, then measured the voltage differential ( only a few millivolts). He checked all the ground and neutral bus bonding screws and found none loose.

He warpped up the inspection declaring it one of the better grounded homes he's seen. We still measured 1.6 Amps at the water line entry. There were much different (fewer) set of appliances running at this visit vs. the first visit.

I fully understand the presence of current at this spot and know that readings can vary quite bit. I have to believe for this house, with significant loading turned on, over 20 Amp reading would not be good, a 10 Amp reading somewhat alarming, and maybe even 5 Amps cause for followup. All I hoped to get with this post was a rule of thumb, but it appears to depend a lot on the home's setup. I also plan to advise this home inspector.

I appreciate all the inputs, the forum has really impressed me.

 

[cadpoint]

There are some many things possible here. When or what the second electrician measured verses the home inspector, first what was the difference in the time of day? If the service lateral is corrupt and the shared neutral is sharing the amps from other's well it's other. If... interal factors of age or wiring has been corrupted inside the house well yes, the Ground can sing that. It's not a one size fits all.

The Poco needs to release the service circuit for a clear reading (testing) of their lines and possible others, one skilled electrician could test the house lines with a meggar, otherwise the exact answer is not presenting.
JMO

 

[don_resqcapt19]

Hank,
Is the water pipe part of a common underground water piping system that feeds other buildings in the area?

Also as a note, it can be dangerous to disconnect the grounding electrode conductor from the grounding electrode if there is current on it, unless you are very sure that there is no problem with the service grounded conductor. If the service grounded conductor is open, you will have line voltage beteen the grounding electrode conductor and the grounding electrode.

As far as checking to see if there is any arc, that doesn't tell you much...it does not take much voltage difference to create a small visible arc.

 

[Handy hank]

More info on this situation. I can get into the new house now anytime. The original current reads are still there and vary from 1.7 to 5.2 amps on the main incoming water line next to where it enters home.
Switched off all branch CBs, verified they indeed shut off all loads, and still read 0.54 amps on main water line and I read 0.52 amps on the service neutral. Therefore we're getting feedthrough and I'm deducing there's a problem with a neighbor's service. Comments?
I also don't read any amperage on GEC to the ground rod in any case. I mean ZERO, no microamps, nothing. The ground rod looks good as do the connections to the rod and panel's ground buss. The ground rod should have no more than 25 ohms resistance to earth ground so a small current should be present. I think there's a problem here too.

 

[dereckbc]

More info on this situation. I can get into the new house now anytime. The original current reads are still there and vary from 1.7 to 5.2 amps on the main incoming water line next to where it enters home.
Switched off all branch CBs, verified they indeed shut off all loads, and still read 0.54 amps on main water line and I read 0.52 amps on the service neutral. Therefore we're getting feed through and I'm deducing there's a problem with a neighbor's service. Comments?

That does not indicate the problem is real or not. If the water pipe system is metallic from your house to your neighbors house, the the water pipe is in parallel with your service neutral and is normal.

Since you are not a pro i am hesitant to say more. If it were me I would call the water department and ask them if a dielectric bushing is installed on your water meter and go from there. If it is not installed what you are seeing is normal. If it is installed call an electrician to inspect service lateral connections and your main panel.

My two cents worth is hope the Water company does not use dielectric bushings. You get the best of both worlds with an excellent ground and redundant service neutral. That is the way the old school designed work until the Water Department caught on and put a stop to it. For some strange reason plumbers and water utility workers did no like being electrocuted when working on water lines.

 

[GoldDigger]

I also don't read any amperage on GEC to the ground rod in any case. I mean ZERO, no microamps, nothing. The ground rod looks good as do the connections to the rod and panel's ground buss. The ground rod should have no more than 25 ohms resistance to earth ground so a small current should be present. I think there's a problem here too.

You have to be careful in how you interpret such a reading (although it may well be that there is an open circuit somewhere).
The ground rod theoretically presents a 25 Ohm or lower impedance connected to the average potential of the dirt surrounding it, which may not be a true earth ground potential if there is substantial current flowing through the dirt in the vicinity of the electrode.

So when you have five amps of neutral current flowing through the water line, that can indicate that the service ground potential (at the POCO neutral at the box where bonded) is not the same as the average "dirt" potential surrounding the water pipe for whatever reason, while the dirt in the immediate vicinity of the ground rod actually is at the same potential as the POCO neutral.

This sort of neutral/ground current is an area where a lot of home inspectors (and even electricians who follow the "rules" without understanding the actual physics behind what they are seeing) can be misled. Hence the high volume of posts on this forum in the Grounding and Bonding topic!!!

PS: The home inspector writes up anything greater than 300ma because he is not qualified or paid to analyze the situation in detail to determine whether there really is a problem or not. Under some circumstances (like an insulated water connection) even 300ma could be an indicator of a potential problem. (See Dereck's post for more info there.)

 

[GoldDigger]

For some strange reason plumbers and water utility workers did no like being electrocuted when working on water lines.

Bringing a whole new meaning to hot water.

 

[dereckbc]

One more clue I can give the homeowner. Go around and turn every light and every gizmo you can. While in the process look at the lights and pay attention to what is going on. If you notice any lights getting dimmer or brighter, gizmos acting strangely, shut off the main breaker, call an electrician and tell him what you did and seen. He will know what is wrong and find the problem. Don't be surprised if he says call the Power Company and follow his directions.

 

[ActionDave]

One more clue I can give the homeowner. Go around and turn every light and every gizmo you can. While in the process look at the lights and pay attention to what is going on. If you notice any lights getting dimmer or brighter, gizmos acting strangely, shut off the main breaker, call an electrician and tell him what you did and seen. He will know what is wrong and find the problem. Don't be surprised if he says call the Power Company and follow his directions.

If he knows what an open neutral at the service does. Not all of them do.

 

[dereckbc]

If he knows what an open neutral at the service does. Not all of them do.

I guess I am just an ole fart because if I were to run into an EC that does not know that symptom tells me he/she is very inexperienced, or needs fired. I am not an electrician and I know it. Maybe I just expect too much.

 

[GoldDigger]

I am not an electrician and I know it. Maybe I just expect too much.

Possibly because with your orientation you like to understand the principles behind things rather than just applying rules by rote?
The instruction-follower can have large gaps in his practical as well as theoretical knowledge.
There have been other threads lately lamenting the fact that many electricians and ECs do not have a theoretical understanding of what they are working with.

 

[ptonsparky]

I guess I am just an ole fart because if I were to run into an EC that does not know that symptom tells me he/she is very inexperienced, or needs fired. I am not an electrician and I know it. Maybe I just expect too much.

I didn't think any of my guys would miss the symptoms but lately when one of them finally had to make the decision on his own he stumbled. I walked him thru the process, just the two of us and I hope it stuck.

 

[ActionDave]

I guess I am just an ole fart because if I were to run into an EC that does not know that symptom tells me he/she is very inexperienced, or needs fired. I am not an electrician and I know it. Maybe I just expect too much.

You would be surprised what a whole lot of electricians don't know. A fair number because they don't care no doubt, but many, even though they are not hacks, do little more than paint by numbers and cash their check on Friday.

 

[kwired]

I fully understand the presence of current at this spot and know that readings can vary quite bit. I have to believe for this house, with significant loading turned on, over 20 Amp reading would not be good, a 10 Amp reading somewhat alarming, and maybe even 5 Amps cause for followup. All I hoped to get with this post was a rule of thumb, but it appears to depend a lot on the home's setup. I also plan to advise this home inspector.

I appreciate all the inputs, the forum has really impressed me.

How much load is running is not what changes the current, it is how much imbalance between lines exists which is when we see an increase of current on the neutral. If you can load the house so there is maximum load on the neutral you very well may find anywhere from a few amps to most of the neutral being carried by the water pipe, and nothing is necessarily wrong with the installation. Whichever path has lower resistance is going to carry more of the current, that easily could be the water pipe in some cases.

 

[templdl]

Can it be determined if the current is originating from the SE of the structure or from an external source which is seeking the neutral/ground of your SE? If it is originating from an external source by trying to find the origins of your water pipe current from an internal source you most likely wouldn't find its cause to be internal.

 

[alder]

More info on this situation. I can get into the new house now anytime. The original current reads are still there and vary from 1.7 to 5.2 amps on the main incoming water line next to where it enters home.
Switched off all branch CBs, verified they indeed shut off all loads, and still read 0.54 amps on main water line and I read 0.52 amps on the service neutral. Therefore we're getting feedthrough and I'm deducing there's a problem with a neighbor's service. Comments?
I also don't read any amperage on GEC to the ground rod in any case. I mean ZERO, no microamps, nothing. The ground rod looks good as do the connections to the rod and panel's ground buss. The ground rod should have no more than 25 ohms resistance to earth ground so a small current should be present. I think there's a problem here too.

I'm new here and it's my first post. I'm wondering if you have a subpanel in the house that happens to have the ground and neutral bonded again and you are measuring a neutral current going through your grounds?