Voltage in pipework, why?

[Stevo99]

Cut a long story short I replaced a weeping tee piece in the cold water pipe at the weekend and as I tidying up got a tingle from the copper pipework when touching the damp concrete.

Measured the voltage (potential difference to earth (the damp patch)) at it was circa 9v DC 

Switched off each circuit at the consumer unit one by on but very little to no change on each circuit. 

Following day (raining) the voltage was only 1.5v DC but investigated anyway. Cleaned the earth clamps (3x) and tested but still the same, 1.5v.

Cleaned the earthing rod contacts outside only to find the 4' copper plated rod corroded down to a measly 150mm in the ground and wasn't solid in the ground. 

Brayed a 3' 15mm copper pipe into the ground and connected up the earth. 

Voltage on internal pipework to the "wet patch" is now .5v DC(half a volt)

Should I be worried about the potential difference to ground?

Am I wasting electricity?

What could be causing it?

Why doesn't it trip the consumer unit?

 

[Andy™]

the voltage may not be coming from your installation... it may be coming into your property from someone else's. which is why metallic pipes etc are equipotentially bonded, to keep any stray voltages like that at the same voltage...

 

[binky]

if it's down to 0.5v I would not be too worried, but I would check again when the weather dries out.

 

[Sharpend]

I would change the copper pipe for a substantial 5/8” earth rod. 

 

[Stevo99]

Ok guys, thanks for the replies.

Can I check some way if the voltage is coming in with my supply?

I'll change the earth rod asap. 

 

[Sharpend]

If you switch off the consumer unit at its main switch, then test. 
I suspect it is a result of your poor earth. 

 

[NozSpark]

Ok guys, thanks for the replies.

Can I check some way if the voltage is coming in with my supply?

I'll change the earth rod asap. 

I'm not questioning you're ability to do this, but how are you going to test it to ensure that it is safe and compliant with the regulations

 

[Stevo99]

Erm.... by checking the resistance?

Got to be better than what was in there! (see image)

Measuring Earth electrode resistance RA

Using a proprietary earth electrode test instrument the Earth electrode resistance test is conducted as follows.

In preparation for the test the installation should be isolated, the earth electrode should preferably be disconnected from the earthing conductor which connects it to the main earthing terminal. If this is not possible, the earthing conductor must be disconnected from the main bonding conductors and other protective conductors at the main earthing terminal, to remove any parallel paths to the general mass of Earth. If such parallel paths are not removed before the measurement is made, an unrealistically low reading of the resistance of the electrode to Earth will be obtained.

With reference to Fig 1, the temporary (current) electrode C2 is placed in the ground some distance away from the installation earth electrode under test. Unless the soil resistivity is very high a distance of around 40 metres is usually sufficient for this purpose. The temporary (potential) electrode P2 is placed approximately mid-way between the other two electrodes.

One reading is taken with P2 in the mid-way position, and a further two readings are taken with P2 approximately 10 % of the overall distance (4 metres) on either side of the mid-way point.

In principle, the instrument passes a current through the ground between the two current terminals C1 and C2. At the same time, the voltage drop between the installation earth electrode and the general mass of earth is determined by means of the voltage (potential difference) at terminals P1 and P2. The instrument then has sufficient information to calculate and display an ohmic value for the resistance of the installation earth electrode under test.

Many proprietary instruments have a facility for checking the resistance of the temporary electrodes. Where the resistance of a temporary electrode is found to exceed the limit stated in the instrument manufacturer’s instructions, the resistance should be reduced to a value within the stated limit.

A sufficient reduction in the resistance of the temporary electrodes may be achieved by driving longer temporary rods into the ground, or by watering the ground in the immediate vicinity of the temporary rods.

The ground adjacent to the earth electrode under test must not be treated with water or brine, as this would make the resistance measurement invalid for the purpose of verification or reporting.

Doesn't every sparkie do this?? 

 

[kerching]

Doesn't every sparkie do this?? 

Nope.... I'd have to look in the book to check

In over 50 years I have installed 2 and tested 3.......and one of the 2 I installed was actually a 36x18 indirect copper HW cylinder that we drove the van over to flatten it then buried I t....so,more of a plate than an electrode

 

[Andy™]

a 36x18 indirect copper HW cylinder that we drove the van over to flatten it then buried I t....so,more of a plate than an electrode

:slap

 

[Sharpend]

Nope.... I'd have to look in the book to check

In over 50 years I have installed 2 and tested 3.......and one of the 2 I installed was actually a 36x18 indirect copper HW cylinder that we drove the van over to flatten it then buried I t....so,more of a plate than an electrode

that’s how to make every pikey cry!! 

 

[Andy™]

that’s how to make every pikey cry!! 

slightly OT, but whilst an apprentice doing heating installs, the van driver would collect any bit of scrap he could (which was then shared between all of us, so he was given all scrap)

one day, amongst the short offcuts of copper pipe on the grass was also a 22mm 3mtr length hammered into the ground sticking up something like 50mm. he spend a while trying to get it out. its probably still there...

 

[Sharpend]

Probably brought the digger round to get it out! Probably a nice pond there now! 

 

[Andy™]

Probably brought the digger round to get it out! Probably a nice pond there now! 

knowing him, thats a possibility. surprised he didnt get a rope around it and the back of the van

 

[kerching]

Back in the day...plumber used to throw all his offcuts down stairwell,and collect at brew time. He always shouted 'below' before he dropped them.  Then they started disappearing as he shouted 'below' and dropped it a little voice shouted 'thank you' and the cut disappeared.  So he heated up a piece of 3/4 copper until cherry red, shouted 'below, dropped it and a little voice shouted 'thank YOOOOOOOOOOOOO'

CHECKED EVERYONES HANDS AT BREAK. new apprentice joiner was then court martialled and tied stark bollock naked to the bus stop for the rest of the day. Police arrived, situation explained, "fair enough " they said. Had a brew and went