House Earthing and copper pipework corrosion

Dubh Geannain

Estate built in the year 2,000.

I've looked for the earth rod for my house a few times but can't find one. I'm not an electrician by trade so am not overly familiar with the wiring regs. Is it possible that a common earth is used for the entire estate? Is that normal practice?


The reason I was looking for the earth rod was I wanted to check the continuity of the entire earth circuit in the house. I've verified that the copper pipework is bonded to the house earth but wanted to check that the house earth itself is well bonded to the actual earth and that and earth leakage current running through the earth circuit is directly to the ground rod and not via the pipework itself.

I performed a test for copper in the house's water supply last night.
At the mains coming in (cold tap at kitchen sink): 0 ppm.
Hot tap at the kitchen sink: 1 ppm
Cold tap from attic tank: 0 - 0.25 ppm (probably closer to 0)

My wife hasn't used the shower to wash her hair for the last year as her highlights were getting a green tinge which we assumed was copper in the mains supply. It now appears some of the pipework is corroding or the hot water tank perhaps which would explain the elevated copper levels in the hot taps. This will lead to a leak somewhere eventually.


Possible causes of the elevated copper include:
Use of dissimilar metals (galvanic corrosion)
Unearthed copper pipework
Housing electrical supply earthed via the pipe due to poor connection/no connection at the earthing rod (corrosion by stray currents)
Leakage current from the shower pump which is connected to both the hot and cold supplies

Fyi: We have a shower pump feeding the ensuite shower. I didn't test the copper levels there yet but would expect the same result as the kitchen sink. A water filtering company measured 1.7 ppm from the shower head last year but they said it was within their allowable limit and couldn't recommend any remedial fixes.

2011

Dubh Geannain wrote: »

Is it possible that a common earth is used for the entire estate? Is that normal practice?

No and no.

The reason I was looking for the earth rod was I wanted to check the continuity of the entire earth circuit in the house.

I think what you mean is that you want to measure the resistance between the extraneous accessible conductive parts (such as pipework) and the general mass of earth? This should of course be a low resistance. However you do not need to locate the earth rod to do this. Remember the resistance between the pipework and an earth rod is of little use if there is too a high resistance connection between the earth rod and the soil. An earth rod installed in very dry stoney ground can provide a very high resistance connection to earth when compared to an identical earth rod driven into damp soil.

It would be best to get a Registered Electrical Contractor to assess the situation properly.

I've verified that the copper pipework is bonded to the house earth

How?

earth leakage current running through the earth circuit is directly to the ground rod and not via the pipework itself.

Any earth leakage current should be so tiny that it will not matter. These currents will take multiple parallel paths to earth, there is no practical way to ensure that all of these currents will flow down the earth rod.

I performed a test for copper in the house's water supply last night.
At the mains coming in (cold tap at kitchen sink): 0 ppm.
Hot tap at the kitchen sink: 1 ppm
Cold tap from attic tank: 0 - 0.25 ppm (probably closer to 0)

I would think that it is more likely that the water itself is acidic and this is causing the copper to corrode.

Possible causes of the elevated copper include:

Leakage current from the shower pump which is connected to both the hot and cold supplies

I would think that these stray currents are of sufficient magnitude to cause issues they should be addressed immediately as there are more serious electrical issues.

Dubh Geannain

Thanks 2011. The funny thing is, since it was initially a water issue I talked to multiple plumbers. None provided me with any further insight. It only dawned on me last night that an electrician might be the better call, hence why I posted in this forum.

I verified the pipework is bonded to the building earth by connecting a multimeter between a power outlet earth and the pipework in the hot press. I have access to a megger though and have measured the earth rod resistance of my own work place as an audit corrective action so have access to Megger too. Have you any thoughts on where the earth rod may be? I'm going to ask a couple of the neighbours anyway.

On the water acidity level. I had the water tested last year. PH level is 7.2 which I think is a safe level.

So the water pump may need further investigation.

I think what you mean is that you want to measure the resistance between the extraneous accessible conductive parts (such as pipework) and the general mass of earth? This should of course be a low resistance. However you do not need to locate the earth rod to do this. Remember the resistance between the pipework and an earth rod is of little use if there is too a high resistance connection between the earth rod and the soil. An earth rod installed in very dry stoney ground can provide a very high resistance connection to earth when compared to an identical earth rod driven into damp soil.

I want to make sure the pipework isn't better bonded to earth than electrical earth of the house. My fear is that the house is earthed through the pipework. I know its not likely since a lot of the plumbing is not conductive, but I want to find that earth rod.

It would be best to get a Registered Electrical Contractor to assess the situation properly.

I'm heading that direction as my head is almost fried at this stage.

Final thought:
Could it simply be a dodgy old tank in the hotpress.

Risteard81

Dubh Geannain wrote: »

I want to make sure the pipework isn't better bonded to earth than electrical earth of the house.

It must be to the MET (Main Earthing Terminal). This will connect it to all exposed and extraneous conductive parts in the house, along with ESB's PEN conductor via your main protective conductor and true Earth will also be connected to this via the earthing conductor and earth electrode.

2011

Dubh Geannain wrote: »

The funny thing is, since it was initially a water issue I talked to multiple plumbers. None provided me with any further insight. It only dawned on me last night that an electrician might be the better call, hence why I posted in this forum.

That is surprising. I know someone that has corrosion issues with copper pipe due to issues with the water. I did not think it that this would be something new to most plumbers.

I verified the pipework is bonded to the building earth by connecting a multimeter between a power outlet earth and the pipework in the hot press.

Ok, assuming that the sockets were wired correctly (therefore connected to the main earth terminal) this should provide reasonable indication. What sort of readings were you getting? These readings would be higher than if you measured directly to the MET as it includes the additional resistance of the earth wire connected between the MET and the socket. Obviously the readings provided by cheap and nasty multimeters can be inaccurate.

I have access to a megger though and have measured the earth rod resistance of my own work place as an audit corrective action so have access to Megger too. Have you any thoughts on where the earth rod may be? I'm going to ask a couple of the neighbours anyway.

Meggar make an entire range of test instruments but are best known for making insulation resistance testers. These would not be suitable for this purpose. What type / model nunnery instrument did you use?

On the water acidity level. I had the water tested last year. PH level is 7.2 which I think is a safe level.

So pretty much perfect.

So the water pump may need further investigation.

Why?

I want to make sure the pipework isn't better bonded to earth than electrical earth of the house.

Why?

My fear is that the house is earthed through the pipework.

Remember if there is no earth fault then there is no earth fault current. Therefore no current flowing in the pipe work even if there was no earth rod or bonding.

If you suspect that you have an earth fault or are generally concerned about the wiring then you should get an electrician to assess the installation.

In the event of an earth fault the current will pass through every available path at the same time. The current will split according to the resistance/ impedance presented to it. Often a large portion of the current will flow along the earth cable to the MET and back to source along the neutral conductor that supplies the installation with very little current flowing through the earth electrode.

Dubh Geannain

2011 wrote: »

What sort of readings were you getting?

Can't recall exactly but less than 20 Ohms

What type / model nunnery instrument did you use?

Megger Met 3/2

I must have misread your point on the water pump. I thought you were suggesting it could be an issue.


I'm involved in safety testing products and a lot of domestic equipment will have earth leakage current. Most products, to meet safety standards, have an allowable leakage current limit of 3 mA and some (such as IT equipment) can get away with 10 mA. These don't equate exactly to the RCD trip level as it also involves an impedance circuit.

I want to make sure the pipework isn't better bonded to earth than electrical earth of the house.
Why?

I might not have clarified too well. So the MET and the pipework is bonded which is good. The next thing I want to check is that the MET is bonded to earth via a decent earthing electrode. If the electrode has a higher than normal resistance to earth then, since the MET it is also bonded to the pipework, I'd be afraid that leakage currents (which will exist at low magnitudes) are running through the pipes which have a lower resistance to actual earth. But as I said previously I don't the plumbing is entirely metallic so it probably is unlikely to be the case. It's just another thing I want to check.

If you suspect that you have an earth fault or are generally concerned about the wiring then you should get an electrician to assess the installation.

I probably will because I can't find the damned earth electrode anyway.

Often a large portion of the current will flow along the earth cable to the MET and back to source along the neutral conductor that supplies the installation with very little current flowing through the earth electrode.

Makes sense and I hadn't considered that.

Yes. I was surprised myself that the plumbers I talked to were not too insightful. The fact my wife's hair was turning green I think threw them a bit as none (out of 3) had ever heard of that happening. And don't get me started about the water treatment companies I spoke to. We had a softener installed when we moved in a couple of years ago too. Regardless of this issue that was probably a good investment though.

2011

Dubh Geannain wrote: »

Can't recall exactly but less than 20 Ohms

That seems quite high.

Megger Met 3/2

That will do it. Obviously if you can't find the earth rod you can't test it in isolation. However using this instrument you can measure the resistance of the MET to the general mass of earth.

I must have misread your point on the water pump. I thought you were suggesting it could be an issue.

My bad, I forgot an "if". What I should have said was "I would think that if these stray currents are of sufficient magnitude to cause issues they should be addressed immediately as there are more serious electrical issues".

Most products, to meet safety standards, have an allowable leakage current limit of 3 mA and some (such as IT equipment) can get away with 10 mA.

You are correct, many devices have a small leakage current when operating properly. However as the device is functioning correctly these currents can not be described as "earth fault currents".

I might not have clarified too well. So the MET and the pipework is bonded which is good

Well the integrity of the bonding is questionable. It would be best to measure the resistance between the MET and the pipework.

The next thing I want to check is that the MET is bonded to earth via a decent earthing electrode.

Earthing and bonding are good, but lets not overstate the importance of an earth electrode. A "normal domestic earth rod" could be anything from 100 to 300 ohms resistance to earth from the MET. Where as the resistance from the MET to the star point of the supply transformer may be just an ohm or two (on a neutralised installation). The earth fault current will split accordingly. The earth electrode basically provides a local earth reference to the installation.

If the electrode has a higher than normal resistance to earth then, since the MET it is also bonded to the pipework, I'd be afraid that leakage currents (which will exist at low magnitudes) are running through the pipes which have a lower resistance to actual earth.

Well as you say these currents are small, so small in fact that they do not cause a problem (unless you have a fault). Besides no matter how well you bond the pipe work the current has to flow along the pipe to get to the bonding stars and from that to the cable.

Even an industrial style earth pit is unlikely to make any difference.
There is something else going on I would think. I have seen old houses with no earth rod or banding that have no issues with copper corrosion.

The fact my wife's hair was turning green I think threw them a bit as none (out of 3) had ever heard of that happening.

Funny, this happened to my mother many years ago :D We had no corrosion issues though. However I did read about acidic water causing this.

brightspark

Is your water "soft"?

Softened water can corrode pipes.

Tuco88

Why not do an earth fault loop impedance test on a socket circuit or DB if your happy enough too, it will soon tell you your earthing situation.

Wild thought..

What are the culprits for copper erosion/oxidation.
Electrolysis maybe?

If you have a very old house the water main is most likly lead and the used to attach an earth to this.

If you have an open vented heating system I have seen idiots pipe the expansion into the main water tank contaminating it.

2011

Tuco88 wrote: »

Why not do an earth fault loop impedance test on a socket circuit or DB if your happy enough too, it will soon tell you your earthing situation.

The earth rod could be disconnected in a TNCS installation and still have an excellent earth fault loop impedance. Why? Because generally the earth rod only provides a parallel return path for a small portion of the fault current.

Tuco88

Is he not trying to test to see what kind of earthing he has? I may have miss read it. Built in 2000 should be pretty decent.

He can carry out an earth fault loop at the Distribution board remove the main earth and test he will know if he has an Earth electrode present by the measurement.

2011

Tuco88 wrote: »

Is he not trying to test to see what kind of earthing he has? I may have miss read it. Built in 2000 should be pretty decent.

He can carry out an earth fault loop at the Distribution board remove the main earth and test he will know if he has an Earth electrode present by the measurement.

That is true, but even with the main earth disconnected there are likely to be a few more paths to earth than just the earth rod.

Dubh Geannain

brightspark wrote: »

Is your water "soft"?

Softened water can corrode pipes.

The issue was present before we decided to get the water softener. We gave the softener a bit of time to see if it made any improvement. It did not aside from reducing limescale buildup of course.

You've highlighted another possible candidate for the corrosion though. Pitting. But I'm not sure any of these conditions are present.

Copper (Pitting) Corrosion
There are many forms of corrosion, but pitting corrosion is most likely to culminate in pinhole leaks in copper plumbing.
Pitting corrosion is the non-uniform localized attack of the wall of copper tube, pipe, or fittings initiated on the inside surface of copper water pipes. Usually only small areas of the metal surface are attacked.
Pitting corrosion can be classified into three types:
Type I cause: Hard Water
Type I pitting is associated with hard or moderately hard waters with a pH between 7 and 7.8, and it is most likely to occur in cold water. The pitting is deep and narrow, and results in pipe failure.

Type II cause: Soft Water
Type II pitting occurs only in certain soft waters, with a pH below 7.2 and occurs rarely in temperatures below 140° F. The pitting that occurs is narrower than in Type I, but still results in pipe failure.

Type III cause: Cold, Soft Water High PH
Type III pitting occurs in cold soft waters having a pH above 8.0. It is a more generalized form of pitting, which tends to be wide and shallow and results in blue water, byproduct releases, or pipe blockage.

http://www.repairmyleak.com/about/failure-copper.htm

Although "Type I" may still be a candidate due to the water being still a little hard (I need to figure out how to tune our water softener settings) and having a pH of 7.2.

Dubh Geannain

@2011. I'm going to bring the Megger home with me this evening and check at the weekend. When I said less than 20 Ohms with the multimeter, I'm sure it was even less than 10 Ohms.

@Tuco88 - The earth fault loop test is probably something I'll need the Electrician for as I don't have a tester for that.

But I'll report back what I find. If I'm getting unusually high resistances anywhere I'll be calling in the electrician. So I'm going to check using the Megger:
Pipework to MET again
MET to earth
Pipework to earth

aido79

Dubh Geannain wrote: »

@2011. I'm going to bring the Megger home with me this evening and check at the weekend. When I said less than 20 Ohms with the multimeter, I'm sure it was even less than 10 Ohms.

@Tuco88 - The earth fault loop test is probably something I'll need the Electrician for as I don't have a tester for that.

But I'll report back what I find. If I'm getting unusually high resistances anywhere I'll be calling in the electrician. So I'm going to check using the Megger:
Pipework to MET again
MET to earth
Pipework to earth

Make sure you understand how to use the meggar correctly and are aware of any damage they can cause to electronic/sensitive equipment connected to what you are testing.

Bruthal

An actual meggar or testers set for testing insulation resistance is not what is needed for low ohms testing. It would be like measuring the width of a pencil with a device designed for measuring in kms.

Dubh Geannain

deleted

Dubh Geannain

Bruthal wrote: »

An actual meggar or testers set for testing insulation resistance is not what is needed for low ohms testing. It would be like measuring the width of a pencil with a device designed for measuring in kms.

There is more than one type of Megger. Some for insulation and some for low resistance measurements like earth testing.

It's not quite this
http://www.megger.com/eu/products/ProductDetails.php?ID=882

I'm using a Megger DET 3/2 as I mentioned in a previous post.

Didn't get around to it at the weekend. But it's on my to do list.

Bruthal

Dubh Geannain wrote: »

There is more than one type of Megger. Some for insulation and some for low resistance measurements like earth testing.

It's not quite this
http://www.megger.com/eu/products/ProductDetails.php?ID=882

I'm using a Megger DET 3/2 as I mentioned in a previous post.

Didn't get around to it at the weekend. But it's on my to do list.

Notice I said a testers set for insulation testing. Never said a testers with an insulation resistance testing facility on it couldnt be used.

Dubh Geannain

Bruthal wrote: »

Notice I said a testers set for insulation testing. Never said a testers with an insulation resistance testing facility on it couldnt be used.

You said "an actual megger, or testers set for testing insulation resistance, is not what is needed for low ohms testing."

I'm using an actual megger

Bruthal

Dubh Geannain wrote: »

You said "an actual megger, or testers set for testing insulation resistance, is not what is needed for low ohms testing."

I'm using an actual megger

Meggar is now more of a multi test instrument. Previous times they were dedicated insulation resistance testers.

Such a meggar, or a multi test instrument set for testing insulation resistance, is not suitable for testing low ohms items. Low ohms as in relatively low. Insulation resistance tests are for testing cable insulation. Insulation resistance is hundreds of megaohms in value, when the insulation is intact. A 1 megaohm reading would be considered bad even though it is still a high resistance. Use the same tester set for insulation resistance testing on something that has for example 20 ohms resistance, and the resistance tester will say 0.

Now that does not say the tester is not suitable for your needs, just when set in insulation resistance mode, it is not suitable.

brightspark

Dubh Geannain wrote: »

You said "an actual megger, or testers set for testing insulation resistance, is not what is needed for low ohms testing."

I'm using an actual megger

Megger is a term used by a lot of electricians still use to describe an instrument designed to measure MEGA OHMS (millions of ohms), normally used to check insulation resistance etc., they operate at voltages of 250, 500 or 1000V.
If a motor is suspected of having problems you might "megger" it (check its insulation)

However as you rightly point out the company "Megger" now make a variety of test equipment, that can accurately measure both high resistances and low resistances.
Considering that Megger took over AVO more than 50 years ago it's a little surprising, but then many people refer to any vacuum cleaner as a Hoover.

2011

The Megger situation was raised in post #5 and answered by the OP in post #6.

Risteard81

brightspark wrote: »

Megger is a term used by a lot of electricians still use to describe an instrument designed to measure MEGA OHMS (millions of ohms)

To be pernickety it's actually Megohms (not Mega ohms).
As stated, Megger is often used generically to refer to an insulation resistance ohmmeter (aka an insulation resistance tester). Such a term should be discouraged. Megger manufacture all types of electrical test equipment (not just insulation resistance ohmmeters), including multifunction testers. In fact all of my test equipment is Megger equipment including multifunction tester; PAT tester; earth leakage clamp-on ammeter.
In the north for the inspection and testing qualification you would actually be marked incorrect for using any name for the equipment other than that used in the IET's Guidance Note 3 (Inspection and Testing). Therefore a "continuity tester" must actually be referred to as a low-resistance ohmmeter for example. It's better to be precise.