Voltage in shower waste!

[purplemaf]

Hi All,

I am at my wits end here so here goes...

On Monday I was called to a domestic premises with reported shocks occuring while the client was taking a shower. This was apparently first noticed over 2 weeks ago!

We proceeded to do all the relevant checks on Earth Bonding and various testing including IR on all circuits. Most circuits proved to be fine apart from a high Zs (3.06) on the upstairs ring. All bonding was proved to be sound. Install is a PME with a split board with only 1 RCD. Main incomer has a Zs of 0.26. I moved all circuits over to RCD protection to see if any tripping would occur....to no avail.

Upon further investigation we ran a lead out from the board to provide a means of testing in the shower...what is clear is that a voltage of 6v can be meaured between Earth and the actual water in the shower tray but ONLY WHEN IT IS DRAINING THROUGH THE WASTE! This voltage increases to around 18v at least as load is increased around the house.

Upon FURTHER investigation I have now discovered this to be the case on all 3 showers and all basins upstairs. With the basins I actually filled them up, released the plug then could measure the voltage as the water drained...NOT BEFORE. With the showers I ran the water and turned off then measured the voltage again as the water drained. All showers are hot and cold fed with no local pumps.

I have had every circuit apart and individually connected 1 circuit at a time in the board and found that 4 out of the 6 circuits seemed to bring about the voltage. I have also bizarrely placed a lead between the mixer taps and into the water in the plug hole while running the water. This always removes the voltage.

I am left with the only answer that somehow a voltage is finding its way through the waste water and once someone gives it a path then the shock occurs!!

I have had SSE out today checking everything their end....no problems. Contacted the NICEIC...no advice could be given! I've consulted 2 of my so called guru electricians who are stumped. I am hoping that tomorrows investigation of the external wiring will reveal something but I'm not holding my breath!

Somebody please tell me they have come accross this before!!

 

[guest119]

What voltage do you get from a live in the house to the flowing water?
Thinking a voltage coming in from a neibour's fault (different phase).
Therefor if you have 240v available do you get more than that testing to the water?

Boydy

 

[Tridentsystems]

Agree but volts are only present as water drains and is flowing. Op said no reading at drain outside when no flow.

 

[purplemaf]

What voltage do you get from a live in the house to the flowing water?
Thinking a voltage coming in from a neibour's fault (different phase).
Therefor if you have 240v available do you get more than that testing to the water?

Boydy

Definately have not tried this...voltage is only present within the house waste. Nothing present in drain outside where 3 stack pipes meet in pit.

Somewhere the water is carrying a voltage. How much voltage at origin is anyones guess as I could be reduced by the time I'm reading it. It seems more load/more voltage. In fact it was even more voltage every time I added the next room onto the circuit today. All I was doing in this little experiment was adding the feed back into the ceiling rose without switch wires etc. More resistance meant more voltage, about 3-4v each time I added a leg back on.

I cant see why im getting the voltage on all three wastes when it seems they are not connected until outside.....where there is no voltage.....

 

[Lucien Nunes]

Have you had a chance to take readings, under the same conditions with water flowing, of the following set of three voltages:
a) External test spike to MET
b) External test spike to energised water stream
c) MET to energised water stream
If the conditions are identical and the spike outside the resistance area of the fault, then it should prove conclusively which point is being elevated above true earth.

The above checks have been carried out and as you say they are all the same.

I didn't mean to imply the voltages should be the same, only that the conditions should be the same for all three readings. For example, 2V spike-MET, 12V spike-water and 14V MET-water would suggest that the MET is where it should be and the water was 'live' which is what we believe is occurring but as yet have no proof. Whereas 13.5V spike-MET, 0.5V Spike-water and 14V MET-water would show that the fault is on the supply. I was just looking to see if that could definitely be ruled out once and for all.

Exhaustive IR tests would be my preferred next move but I figured you might already have noted those voltages in earlier tests.

 

[Rockingit]

What's puzzling me is even if there IS an IR fault internally, how is that interacting with a waste pipe and how is one part of the waste system not conducting through to another when it's the water inside it that has to be acting as the conductor as effectively flows everywhere.

Has anyone thought to remove the waste traps and see what measurement is the other side of the water trap? My guess is none.

There's something about this whole thing that doesn't quite ring true.

 

[Tridentsystems]

If a screw had nicked a cable and pierced a plastic waste pipe ( unlikely but possible ) then this could happen. Flow won't necessarily be continuous, may only conduct when enough water is flowing to reach a certain level ? Had a similar thing with a drain pump once on a wet room Eco deck. That problem never revealed itself under normal IR tests. Only when client showered and then not enough to trip RCD Floor had 120 v to E at times and was a screw in the end. So easy to put a £20 camera on a draw tape and have a look before ripping bathroom up. Wish I was local I would give a hand for free as I love faults.

 

[UNG]

Wish I was local I would give a hand for free as I love faults.

Was thinking the same myself

 

[Rockingit]

Another part of this mystery equation is that water isn't THAT brilliant a conductor and relies heavily on whatever contaminates it contains instead. Would be interesting to do an IR between the three traps and see how high a reading is obtained. My guess is it will be off the scale still.

Also, if you chuck a decent lump of copper into one of the traps and bond it back to the MET, does the problem go away in the others or remain?

 

[Marvo]

Water itself isn't generally a great conductor but drains usually have a generous coating of slime which conducts pretty well.

 

[purplemaf]

Ok gents here is todays update. Only had a short while at property so I chose to record some IR readings directly to waste water at one of the showers. Also I have double checked and I do definately have 3 seperate stacks that meet in the ground outside.

The following IR readings were taken with each circuit completely disconnected on 500v - 20mohm. I literally had a lead poked into the waste with he water running.

Live to water
Lights Down - 0.62
Lights Up - Clear
Skts Down - 3.07
Skts Up - 0.63
Smokes - Clear
Cooker - 13.55

Earth to water
Lights Down - 0.45
Lights Up - 0.3
Skts Down - 0.07
Skts Up - 0.07
Smokes - Clear
Cooker - 0.08

Water to Met - 0.07
Water to Neutral Bar - 2.45
Water to Bond - 0.08

 

[chcnorris29]

Even if there was a screw in the pipe as there is no voltage at the drains outside where they connect how would you be getting the voltage to the other pipes at the drains in other rooms.

 

[brman]

I think it worth clarifying the answers to Lucian's questions.

He asked about MET to (an unconnected) external earth spike and you implied in your reply you got a voltage there. If you did then doesn't that point to a installation earthing fault?
Or did I misunderstand the Q&A?

2nd question: you say you have experienced this shock. Is it a continuous buzz or a static like short shock?

Lastly, someone suggested testing with an analog meter. I am assuming this was to check whether the voltage held up under a lower impedence load. Did you try that? If you don't have a old meter then maybe something like 100k resistor in parallel with your test leads?

 

[DNS1]

I've not got time to read the whole thread, but this raises an interesting question...

Bonding of incoming gas and water pipes is one of the first things we look for, so why not bonding of waste pipes? I know most are plastic these days, but not all...

 

[Silly Sausage]

I've not got time to read the whole thread, but this raises an interesting question...

Bonding of incoming gas and water pipes is one of the first things we look for, so why not bonding of waste pipes? I know most are plastic these days, but not all...

If they are metal, you would.

 

[Richard]

You say that it is a PME system, are you completly confident that you are getting true neutral? My only thought was that if you had a poor/dropped neutral (externally), possibly you are still getting a good loop impeadance through nearby propertys via waterpipe work, ect?

I think you said DNO had already been so I'm guessing this has already been proven.