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!!

 

[UKMeterman]

This is a PME property? Try putting some earth pegs outside, you don't need to go mad you need to get a Ze of about 1 kohm or better, using a long lead check the voltage between the earth peg and the MET of the property under heavy load. Also check the voltage between the waste and the earth peg first when several buckets of water are being poured through, and then when water is being run from the mixer tap.

It may be there is a metal waste pipe that is at true earth somewhere and the water is bridgeing the gap.

 

[Farmelectrics]

Meterman what would you be hoping to achieve by this the high zs on the ring main wants correcting first but interested to here what your meaning

 

[Marvo]

I feel for you.

http://www.electriciansforums.co.uk...lations/70467-shocks-bath-tap.html#post688922

 

[Farmelectrics]

Agree as above glad it's not me baffling isn't the word book a holiday and disappear for two weeks lol let us no if you solve it and what it was

 

[purplemaf]

LOL,

I just came back from 2 weeks away to this!

 

[purplemaf]

Agreed about the ring main but my priority right now has to be the water issue. I have had every neutral and earth disconnected at the board and the problem still lives. It must be an external anomilie!?!?! I hope...

 

[Hawk]

Are the waste pipes metallic? If so could you bond them?

 

[Marvo]

There are some faults that standard electrical testers will never pinpoint even in the most experienced hands. Sometimes you've just got to bite the bullet, be proactive and get dirty if necessary. If you've done all the tests and none of the results give you any clues where the problem may be then start exposing the shower drain pipe so you can visually check along the full length.

 

[purplemaf]

No I wish they were then it would be easy to remove the voltage! HOWEVER that would not tell me where it is coming from which of course is my biggest concern!