You need to be able to measure very low resistances and with some decent current flowing, to stress the teminations. Your multimeter will be struggling to measure tens of Ohms, with any accuracy, at a few milliamps.
Copper Corrosion on incoming main
- Thread starter DIYinBerks
- Start date
You need to be able to measure very low resistances and with some decent current flowing, to stress the teminations. Your multimeter will be struggling to measure tens of Ohms, with any accuracy, at a few milliamps.
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I take your point Harry, however whilst I have worked in electronics in the security industry I don't have the particular knowledge to be sure of doing more detailed specialist testing. I could buy or hire the instruments but I'd be the chap with all the gear and no idea! Thanks for your interest though.
Let me say first that the OP's problem and your problem seem like they are the same, the lack of proper bonding. All your pipes need to be at the same potential or they will suffer the same fate. That means ensuring all the metal pipework in properly joined together, either by the pipework itself, or if there are sections of plastic installed to be linked around the plastic and overall bonded to the earth terminal.
Any electrically isolated bits can have a potential appear across them and it doesn't need to be much, a potential which can eventually erode away the pipe.
Lacking proper equipment, one way might be to use a volt meter, connected between the main earth terminal and any suspect pipework, on the 1000v ac range, gradually adjusting the meter's range down to one volt. There should be no potential difference.
It's by no means a substitute for a proper earth loop test, but it might show up an issue.
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There is one short length of plastic pipe and that is where the outside tap is tapped into a spur off the incoming main. Other than that all the pipework that I can see is copper. It will be a simple matter to connect the two copper lengths via a suitable length of earth cable.
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Not at all, John, I'm sorry if I have given that impression. As far as I can see the plumbing is already bonded to the main earthing point with the exception of the short length to the outside tap. The photograph of the meter cupboard that I added to my reply to your first post shows numerous earth cables going off to various parts. I assume they provide a common potential across the electrical and water system. As for this short length to the outside tap, I occurs to me that it would actually be easier to bond it direct to the main earthing point as it passes within a about 30-40 cm of the meter cupboard.
Having had a few 240Vac shocks over my lifetime and survived to tell the tale, I am all-for maximum safety!
that should do the trick
now I look at your photo, I see you have a handsome 8-way earth block available.
You should bond to the incoming metallic pipe at the point it enters the house, usually within 600mm
Although the pipework inside the house should be bonded, the outside tap, if it is isolated with plastic pipe, does not need to be separately bonded, and should not be.
see https://www.diynot.com/wiki/Electrics:main_equipotential_bonding
now I look at your photo, I see you have a handsome 8-way earth block available.
You should bond to the incoming metallic pipe at the point it enters the house, usually within 600mm
Although the pipework inside the house should be bonded, the outside tap, if it is isolated with plastic pipe, does not need to be separately bonded, and should not be.
see https://www.diynot.com/wiki/Electrics:main_equipotential_bonding
Thanks again John. 
p.s.
you appear to have a TNS supply, and a pipe clamp on the armour or metal sheathing of the supply cable. This is not very good, and if you ask your Distribution Network Operator, they might provide you with a better earthing point, possibly free.
The DNO is not the company you buy your electricity from, but will be shown on your electricity bill, probably near the bottom, near your meterpoint (Supply) number, which begins with an "S," which you should quote. It will say something like
"If you need to contact your local network operator, call
0800 nnn nnnn or write to
Bloggins Electricity Distribution PLC, 1 Streetname, Anytown, PC1 8XY."
If you mention the earth is by a pipe clamp on the cable sheath, an engineer will understand.
Don't touch the clamp yourself. It is possible (but unlikely) for the clamp to bite into the cable if it is too tight.
A short letter will be more effective than a phone call, because the call centre operators are often unfamilar with this work.
you appear to have a TNS supply, and a pipe clamp on the armour or metal sheathing of the supply cable. This is not very good, and if you ask your Distribution Network Operator, they might provide you with a better earthing point, possibly free.
The DNO is not the company you buy your electricity from, but will be shown on your electricity bill, probably near the bottom, near your meterpoint (Supply) number, which begins with an "S," which you should quote. It will say something like
"If you need to contact your local network operator, call
0800 nnn nnnn or write to
Bloggins Electricity Distribution PLC, 1 Streetname, Anytown, PC1 8XY."
If you mention the earth is by a pipe clamp on the cable sheath, an engineer will understand.
Don't touch the clamp yourself. It is possible (but unlikely) for the clamp to bite into the cable if it is too tight.
A short letter will be more effective than a phone call, because the call centre operators are often unfamilar with this work.
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Again John, thank you.
Looking through these two threads I cannot see if anyone has measured the AC voltage between the neutral and the house earth.
Ideally this will be fairly low but usually just 2 or 3 volts. It can also vary according to the current being used within the property.
Another test could be to measure the voltage between the house cable sheath earth and the real earth potential as defined by an earth rod in the garden.
While on holiday in the Seychelles I got a mild shock in the shower from the head earthed to the mains earth and the waste at the real earth potential. It was about 36vac difference.
This was caused by the mains earth being connected to the neutral star point at the nearby transformer. However due to imbalance in the loads between the three phases the star point can vary significantly from the real earth..
I try to take a small multi meter with me on holiday. It was very useful there because the dentist had just had a new Japanese dental chair delivered and it would not move both up and down. I discovered that the limit switch had been wrongly connected. So much for maker's testing! Hate to think what he would have done if I had not been there to fix it for him.
Ideally this will be fairly low but usually just 2 or 3 volts. It can also vary according to the current being used within the property.
Another test could be to measure the voltage between the house cable sheath earth and the real earth potential as defined by an earth rod in the garden.
While on holiday in the Seychelles I got a mild shock in the shower from the head earthed to the mains earth and the waste at the real earth potential. It was about 36vac difference.
This was caused by the mains earth being connected to the neutral star point at the nearby transformer. However due to imbalance in the loads between the three phases the star point can vary significantly from the real earth..
I try to take a small multi meter with me on holiday. It was very useful there because the dentist had just had a new Japanese dental chair delivered and it would not move both up and down. I discovered that the limit switch had been wrongly connected. So much for maker's testing! Hate to think what he would have done if I had not been there to fix it for him.
Not just the current being used within the property, but other properties near by and on the same sub-station outlet.
Corroded copper metal and "stray" voltages can create some interesting results. Oxidised copper can create a diode that when an AC voltage is applied to it produces a DC current ( half wave rectification )
Take the case of a copper pipe in good contact with damp ground and corroded, this has the potential ( pun intended ) to create a diode between pipe and ground..
Apply the potential difference between the imported "Earth" ( from the PME Neutral ) and the true Ground potential across this diode and the resultant current will have a DC component. This DC current can then unpredictably affect other items in the electrical / plumbing / earthing system
How to make an intentional copper oxide rectifier ( diode ) http://halestrom.net/darksleep/blog/011_copper_diodes/ ( other methods are available ).
Take the case of a copper pipe in good contact with damp ground and corroded, this has the potential ( pun intended ) to create a diode between pipe and ground..
Apply the potential difference between the imported "Earth" ( from the PME Neutral ) and the true Ground potential across this diode and the resultant current will have a DC component. This DC current can then unpredictably affect other items in the electrical / plumbing / earthing system
How to make an intentional copper oxide rectifier ( diode ) http://halestrom.net/darksleep/blog/011_copper_diodes/ ( other methods are available ).
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Thread revival!
I have had another perforation of the incoming cold water main, just like the previous one and within only a couple of metres of it.
Having been through all the sage advice of contributors earlier in the thread, I have had a thought. This trouble coincidentally started soon after the water main buried under my front lawn was replaced. The original main was almost certainly installed when the house was built in about 1968, and was probably metallic - iron or copper. It is now HDPE and will no longer offer any earth connection. This means that the earth bonding clamp connected immediately adjacent to the incoming stop valve just inside my basement has no longer any electrical connection with the buried incoming main.
The earth cable from this earthing point goes eventually to the earthing terminal block in the meter cupboard. My question is would it be better to remove this earth clamp and bond the pipework from the opposite end which is near the incoming mains supply terminal?
Replacing the cold water mains from stop valve to the various places it serves would be a major plumbing job and if relocating the earth would help to reduce the risk of further leaks then I'm all for it! I can also reduce the incoming water speed without detriment to appliances as the house is on a very high pressure supply and speed of flow and turbulence could be negative factors too. If the isolating valve is throttled back the peak flow rate would be lowered by adding resistance. Pressure would of course remain the same in no-flow situations.
Any thoughts would be appreciated please, thanks.
I have had another perforation of the incoming cold water main, just like the previous one and within only a couple of metres of it.
Having been through all the sage advice of contributors earlier in the thread, I have had a thought. This trouble coincidentally started soon after the water main buried under my front lawn was replaced. The original main was almost certainly installed when the house was built in about 1968, and was probably metallic - iron or copper. It is now HDPE and will no longer offer any earth connection. This means that the earth bonding clamp connected immediately adjacent to the incoming stop valve just inside my basement has no longer any electrical connection with the buried incoming main.
The earth cable from this earthing point goes eventually to the earthing terminal block in the meter cupboard. My question is would it be better to remove this earth clamp and bond the pipework from the opposite end which is near the incoming mains supply terminal?
Replacing the cold water mains from stop valve to the various places it serves would be a major plumbing job and if relocating the earth would help to reduce the risk of further leaks then I'm all for it! I can also reduce the incoming water speed without detriment to appliances as the house is on a very high pressure supply and speed of flow and turbulence could be negative factors too. If the isolating valve is throttled back the peak flow rate would be lowered by adding resistance. Pressure would of course remain the same in no-flow situations.
Any thoughts would be appreciated please, thanks.
That looks like electrolytic erosion. I would suggest checking for voltage differences between that copper pipe, and your main electrical earth.
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