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!!

 

[purplemaf]

Just checked outside electrics (only 1 twin skt on house wall)...no problem there. Also checked for voltage in the actual drainage outside the front door. No voltage present.

 

[UNG]

Have you tried an IR / continuity test on the waste to L & N and the main earth

Also what type of meter are you using to get your voltage readings

 

[Lucien Nunes]

If the voltage is absent with some circuits off, and remains absent even when there is load on other circuits, and the Ze is OK, that would suggest a localised insulation fault rather than external. If the insulation has broken down to some pipework or structural metal that is not bonded your original IR test might not have revealed it. How about earthing the water flow and repeating the IR test on suspect circuits.

 

[newbec]

If the voltage is absent with some circuits off, and remains absent even when there is load on other circuits, and the Ze is OK, that would suggest a localised insulation fault rather than external. If the insulation has broken down to some pipework or structural metal that is not bonded your original IR test might not have revealed it. How about earthing the water flow and repeating the IR test on suspect circuits.

I agree with this. Also have you completely removed all connections to the installation when carrying out Ze and also tested loop impedance of the supply between Line and Neutral and compared it with the Ze result to ensure the PME link in the service head is intact and the external return path is effective?

 

[purplemaf]

Hi Gents thanks for all the posts....unfortunately this is still not resolved.

I have once again worked through all circuits and was convinced I was closing in on he problem. I connected each circuit individually and switched on to see which were giving a voltage. I had done this before. I found that only the upstairs lighting gave me 16v. So I started looking closer at the lighting leg by leg taking r1+r2 readings as I went along. Each room increased the reading by roughly 0.4 ohms. Overall the Earth loop reading was 2.36. I put it back together adding each room to the circuit and testing the water. The voltage in he water started very low and increased every time I added another room. HOWEVER once I finished this process I decided to completely disconnect the lighting and power the rest of the house back up. The voltage again returned at 5/6v

I tried converting to TT.....still there. Ran a bond to upstairs straight from board...still there....

 

[Tridentsystems]

So is it there constantly or just when waste is full of water ?

 

[purplemaf]

Just when the water is going through the waste. I can watch the voltage reduce as the water disappears

 

[KAS1]

What dangerous voltage levels are we talking about here !!!!!!!!!!!

 

[Richard Burns]

What dangerous voltage levels are we talking about here !!!!!!!!!!!

18V well below the level of detection by touch!

 

[Silly Sausage]

Really difficult to know what's occurring here and advise!







How about fitting a metallic waste trap on these shower basins and bonding them to the shower mixer taps... :ninja::38:

 

[purplemaf]

If that were the case I would never have had the call....I have felt this shock and it can certainly let you know it is there!

 

[purplemaf]

Ive been through the idea of having a metal waste put in. First plumber ive spoken to tells me metal traps dont exist?? I'm also not so happy to conclude with that idea as that doesn't answer the problem of where its coming from.

 

[chcnorris29]

Is the voltage there if the water in the waste is from an external source (bucket of water) or just when it comes from the taps of the installation?

Thanks.

 

[purplemaf]

Fair question. It is literally in the tray/basin with the taps/shower turned off and water draining.

 

[Silly Sausage]

Someone did ask earlier, how exactly did you test for this voltage.
What instrument did you use, where did you test from and to, including multiple locations of both points.
Only asking because it may shed more light on the problem.

I'm also assuming that the shower taps are fed from a remote boiler, i.e., not a local electric shower.