"live" waterpipe

[bengasman]

Got a call about a leaking waterpipe that could not be repaired because it was live.
Tested it, and sure enough 55 volts on it.
Checked CU, (split load 1 rcd) feed from what looked like 16mm2 t&e, 2 10mm2 y/g disappearing in the floor, presumably to water and gas but could not inspect as the floor could not be opened.
Turn main breaker and n-e goes from 55V to 6 V.
Breaker back on and n-e back to 55 v.
The more mcb's I turn off, the lower the n-e, but 3 in particular (10-20 volt each) and the rest just 1 or 2 volt difference.

the flat was created by a developer who split up a house into 4 flats, and after that disaster it was "improved" by a builder.

Anyone got some pointers where to start looking, or is it a typical case of disconnect and test/inspect the lot?

I am qualified to work on electricity, but my corebusiness is heating and this one puzzles me somewhat

 

[chivers67]

What water pipe is it and whereabouts??

Is supplementry bonding present anywhere?

 

[Spark123]

Main bonding in place?

 

[securespark]

Got a call about a leaking waterpipe that could not be repaired because it was live.
Tested it, and sure enough 55 volts on it.

55 V between pipe and ????

Checked CU, (split load 1 rcd)

So all circuits isolated by main switch, but some circuits protected by RCD?

Turn main breaker

What did you turn off? The Main Switch or the RCD?

n-e

Need to verify gas and water PEB's: what is there adjacent to the stopcock & gas meter in the way of PEB's?

 

[Spark123]

What is the Ze reading too?

 

[bengasman]

What water pipe is it and whereabouts??

Is supplementry bonding present anywhere?

Believe it or not, the incoming mains

Supplementary bonding very neat and measures 0.0 on all combinations.

 

[Spark123]

Thinking outside the box - is it the water pipe raising above earth potential or is an open circuit CPC/earthing conductor causing the electrical system exposed conductive parts to all raise above true earth, escallated by no Protective Main Bonding in place?

 

[bengasman]

Main bonding in place?

2 10mm2 from earth bar in CU, but unable to see where they go because the floor can not be lifted.

 

[securespark]

That is why I wrote:

what is there adjacent to the stopcock & gas meter in the way of PEB's?

 

[Spark123]

Should be within 60cm of entry to the building and before any tees.
If you can find the other end you can find out if the cable is continuous by connecting a wander lead to it at one end and measuring the resistance at the other end, subtracting the resistance of the wander lead.

 

[bengasman]

Got a call about a leaking waterpipe that could not be repaired because it was live.
Tested it, and sure enough 55 volts on it.

55 V between pipe and ????

Checked CU, (split load 1 rcd)

So all circuits isolated by main switch, but some circuits protected by RCD?

Turn main breaker

What did you turn off? The Main Switch or the RCD?

n-e

Need to verify gas and water PEB's: what is there adjacent to the stopcock & gas meter in the way of PEB's?

55v between pipe and earth on CU

55V goes to 6V when turning off main breaker and down to 20V with main breaker on, but RCD off.

n-e : neutral - earth

Can not veryify PEB as floor can not be lifted.

 

[bengasman]

What is the Ze reading too?

Did not measure Ze.

 

[Spark123]

Thinking outside the box - is it the water pipe raising above earth potential or is an open circuit CPC/earthing conductor causing the electrical system exposed conductive parts to all raise above true earth, escallated by no Protective Main Bonding in place?

I'll have my 50p on this

Try doing a Ze test and see what you get. Main PEBs need sorting as a priority.

 

[bengasman]

Thinking outside the box - is it the water pipe raising above earth potential or is an open circuit CPC/earthing conductor causing the electrical system exposed conductive parts to all raise above true earth, escallated by no Protective Main Bonding in place?

this is where it starts getting really confusing; INSIDE the flat not exposed conductive parts seem to have a problem.

My first guess was loose earth or equipotential bonding, but all connections inside the CU are present and properly connected, as is supplementary bonding.

The other problem is that the builder decide to use sheets of board for the floor and screw them as well as glue them down.
I can't inspect the main bonding connections without doing some serious damage to the floor.

 

[Spark123]

Yep - it is the opposite of what you expect but is perfectly plausable. If everything in your faraday cage is at 55v above earth then you can safely move around in it. Introduce something earthy at 0v and they you have a 55v potential difference which can be a problem.

Like I say - try the Ze first (in isolation) and see what you get. As you have 55v between the water intake and the consumer unit it sounds like the main PEBs are not in place which means the water pipe can introduce a potential into your equipotential zone (faraday cage) that is different to everything else in there so if I am correct there are a number of problems which need addressing.