Yes
"live" waterpipe
- Thread starter bengasman
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bengasman, why are you ignoring everything Spark123 has said to you ? The others are skirting around the problem. Spark has nailed it IMO.
Having seen the building, I don't exclude any possibility. When I go back, I will have to check the various options.
As the 4mm2 cpc from the feeding T&E is without doubt insufficient, I will start with a proper cable from the DNO MET to the CU earth bar, and from there at least 10mm2 to gas and water, as a PEB that is not visible, is not reliable. I've got a mind to connect the communal water to the communal MET whilst I am at it.
After sleeping on it, I wouldn't be surprised if the old lead pipe was used as the main earth when they built the house.
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When would that have been? Pre-'66 it could well have been done.
Pre WWII somewhere.
The dodgy developer that split the house into 4 flats did not exactly improve things, and the builder that "revamped" the flat after that seemed more interested in looks than in quality.
Does that give you an idea about the technical state of things?
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Think so.
[Gallop of hooves fades into dusty distance]
[Gallop of hooves fades into dusty distance]
ricicle said:
Having read the entire thread more carefully, I agree. A simple pipe to neutral measurement should nail it. But then we have this --
bengasman said:
My best guess would be that the neighbour's pipe is actually the live one.
Somewhere between the two pipes there must be a high resistance section (plastic). Your pipe is connected to true earth through the incoming water main but your wiring earth is floating free, being connected neither to true earth nor the pipe. The neighbour's pipe is floating free of true earth but it IS connected to the faulty wiring earth.The varying voltage you see on your earth wiring (NOT on the pipe) will be capacitive coupling from live wires. The more of them you switch on, the higher the voltage rises. Check the voltage between pipe and earth with a light bulb in parallel with your meter and watch it fall to zero.
The varying voltage you see on your earth wiring (NOT on the pipe) will be capacitive coupling from live wires. The more of them you switch on, the higher the voltage rises. Check the voltage between pipe and earth with a light bulb in parallel with your meter and watch it fall to zero.
Surely that will be increasing INDUCED voltage rather than capacitive as it is the current increasing in the cables when extra lights are switched on..........
ricicle said:
Inductive coupling between current-carrying wires in mains circuits is negligible. What you have is a capacitive potential divider with the floating earth in the middle.
On the live to earth side you have the live wires in all cables that are On. On the neutral to earth side you have the neutral wires in all cable at all times AND the live wires in cables that are Off, because the loads on these cables are pulling the switched lives down.
A ball park figure for inter-wire capacitance in most cables is 100 pF per metre. This means that 100m of cable has a capacitance of 10 nF and this has a reactive impedance of about 320 kohms at 50 Hz. That's too high to light a lamp but it'll show voltage on most meters.
I took it to mean between the earth rail in his CU to any of those three other points?bengasman said:
My best guess would be that the neighbour's pipe is actually the live one.
Still - the main PEBs can't exist as they would hold the water pipe at about the same potential as the MET.
N - E reading at the CU giving 55v says there is a problem with the main earthing. Icing on the cake would have been to do a Ze check. The gradual increase as circuit breakers are closed I'd put down a capacitive effect.
One thing is for sure, at least 2 flats don't have a proper earth, or proper PEB, so they will get it. I reckon that will solve the problem.
Once that is done, I will take various Z readings and take it from there. I will post the findings.
Thanks for all the input so far.
Once that is done, I will take various Z readings and take it from there. I will post the findings.
Thanks for all the input so far.
Result!
New 25mm2 earth cable to DNO and voila, Z down to 0.23.
Turned out that the earth to the CU was only connected to the breaker housing, which in it self had no further connection.
The lead water pipe was used as earth provider after all.
Thanks for all the help.
New 25mm2 earth cable to DNO and voila, Z down to 0.23.
Turned out that the earth to the CU was only connected to the breaker housing, which in it self had no further connection.
The lead water pipe was used as earth provider after all.
Thanks for all the help.
Yessireebob. The whole kit and kaboodle, main connection 25mm2, gas and water 16m2 and supplementary 10mm2.
I know it is a bit over the top, but my motto is: better have it and not need it, than need it and not have it.
And it looks impressive, I always do it when given half a chance and it works a treat.
I always ask clients if they want the minimum required, or well oversized for 10% extra. Funnily enough, the recession has made no difference to the ratio of choices; 100% want the extra for a few bop more.
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