"live" waterpipe

[bengasman]

16mm twin and earth is fine providing it is adequately protected and volt drop is not excessive.

16 ohms is a bit over the top too. As some of the flats are reading OK it says that the earthing is fine to them from the building MET so the DNO side of it is probably fine. Have a peep in the metering room / cupboard and all will probably be revealed.
A 16mm from building MET to flat MET should be fine, providing of course the Zs is sufficiently low.

Still - even once the main issue is fixed, don't let them get away without sorting main bonding!

Hope this helps - at least it gives you something to go and look at!

Yes, this helps indeed.
Current plan of action.
16mm2 from MET to MET
Forget the existing PEB, and put new one in, visible and all.
test and measure again, and take it from there.

Thanks for the input.

 

[securespark]

The bit that really puzzles me is how a pipe ( a big fat lead one) can be live on one floor, and perfect on the next.

On a similar line to my previous post, are the two properties with dicky Ze's on the same floor, sharing the same pipe?

I suppose what you say could ring true if there were an insulating pipe joint somewhere making the pipes effectively two separate pieces isolated from each other.

 

[Spark123]

How I think it is:

It isn't the pipe that is wrong. That is fine and at 0v with respect to mother earth.

It is the electrical installation that is wrong - with a floating earth it is rising to 55v above mother earth.

You stick your meter on and measure 55v as there is a potential difference between the two - the meter doesn't tell you which is at the wrong potential! You assumed the pipe, I think the pipe is fine and the electrical installation is to blame.

There is a fault on the main earthing of the flat allowing the electrical installation earthed metalwork to rise to 55v above mother earth, and the neutral conductor which it should be similar to.

The bonding is also incorrect as this should tie everything together so there isn't a risk of their being a potential difference.

 

[bengasman]

Zs readings in 2 of the 4 flats about 0.4, one impossible to read, and one 18.

Just a brief flash of a thought B4 I hit the sack:

Could it just be possible that the flat with the high Ze and the one with the unmeasureable Ze have their supplies linked somehow at the service end?

You could do with taking a Ze on the incoming side of both switchfuses for these flats and a Ze on the outgoing side.

unlikely that they are linked, but anything is possible here.
The dno side is fine, it is the builder who cocked things up.
Do you mean by switchfuse, the breaker on the CU, or the distributor cut out?

 

[securespark]

Current plan of action.
16mm2 from MET to MET
Forget the existing PEB, and put new one in, visible and all.
test and measure again, and take it from there.

Thanks for the input.

I'd still be tempted to check the Ze's.

I can't remember if you'd identified the size of the fuse protecting the submain.

 

[bengasman]

The bit that really puzzles me is how a pipe ( a big fat lead one) can be live on one floor, and perfect on the next.

On a similar line to my previous post, are the two properties with dicky Ze's on the same floor, sharing the same pipe?

I suppose what you say could ring true if there were an insulating pipe joint somewhere making the pipes effectively two separate pieces isolated from each other.

Different floors, same pipe, but electrically isolated by bit of plastic used for repair of leak.
The live pipe is between the flat I tested, and the one below. Between where I can see it go into the ceiling, and the stopcock is about 1 metre that I can not see. Even if there was a plastic joint between the copper that I can see, how does that explain the 55 V both on the pipe and in the CU?
I will bring sufficient fly lead next time and measure the resistance between the lead pipe and the copper. Put my money on low resistance.

 

[bengasman]

Current plan of action.
16mm2 from MET to MET
Forget the existing PEB, and put new one in, visible and all.
test and measure again, and take it from there.

Thanks for the input.

I'd still be tempted to check the Ze's.

I can't remember if you'd identified the size of the fuse protecting the submain.

Will check all Z's when I am there; pretty important bit.
distributor cut out for each flat is 100A.

 

[securespark]

The Dist. Cut-out, yes. But there should be some fusing down between there and the CU in the flat, as 16mm² T&E is only tabulated at 85A at best.

I had a flat complex to go to once. Two things struck me as odd about it straight away. There was an RCD incomer in the cellar for each flat. Very convenient!

And that RCD was the only thing between the 100A Dist. cut-out and the 10mm² T&E feeding each flat! Not fused down.....

 

[securespark]

Really am off to bed now! Good luck with it - post an update asap!

 

[bernardgreen]

Years ago I had a similar scenario in friend's flat. As a mere amateur my opinion that the earth to one flat was at fault was dimissed by the electrician ( or was it the engineer from the electricity company ) as ignorance. Fortunately ( for the tenants ) the landlord had a bit of knowledge and trusted me.

Measuring the voltage between mother earth and the earth on the sockets in the four flats proved the 4 earths in the flats were not all connected to to the same point as there were two at zero volts to mother earth, the other two flats had floating earths.

 

[Space cat]

I will bring sufficient fly lead next time and measure the resistance between the lead pipe and the copper. Put my money on low resistance.

Go one better. bring enough wire to reach from the MET to anything you might want to reach. This will give you a single reference point for all your voltage measurements.

 

[bernardgreen]

That assumes that the MET is a good earth.

Use an earth rod as a reference 0 volt for the meter and check the MET is in fact a good earth and is not several volts above "mother earth's" voltage.

 

[Space cat]

Use an earth rod as a reference 0 volt for the meter and check the MET is in fact a good earth and is not several volts above "mother earth's" voltage.

That's a fair point but I would still use MET as the reference and measure from there to real earth. Just a personal preference. Also, when measuring to a neutral or (supposed) earth point, make at least two measurements: one on minimal load and another on heavy load.

 

[bengasman]

I will bring sufficient fly lead next time and measure the resistance between the lead pipe and the copper. Put my money on low resistance.

Go one better. bring enough wire to reach from the MET to anything you might want to reach. This will give you a single reference point for all your voltage measurements.

That would be ideal, but not very practical here and I doubt the people will be willing to fork out for it.

 

[VanSolo]

Just a thought. Is the polarity correct on the incomers of the CU?