how about this, i wont bore you with all the small talk..

i have a customer who bath becomes live when they pull the plug out???

tested the house all ok.. bath is bonded.. house on rcd,, the current is only small like a tingle,,

when you put the plug in it stops..

any ideas i have none at all

Gidday there Paul,
Long time no see!.
Well here's one for the books, I can't say I've heard of anything like this before.
Only advice I can offer however, is, it may pay to check the Neutral connections at the Main switchboard, as I have a feeling one of them may be loose.
Just a wild guess.
Only other thing I would suspect, which is even more remote, would be RF currents getting into the pipe-work.
BTW, is the bath body bonded to the drain?.
I'd get a voltmeter and test to a known Earth point, something sounds a bit wierd here.

Like something out of Hammer House...

Have you checked the drain run? Is it in copper ( like mine ) or cast iron? Where is it discharging? And exactly what is bonded?

And yes - check the neut terminal, main earth bond and PME. Look for no-volt on the PME path ( needs a temp rod unless there is already one in ).

Bizarre!!

Maybe it is not the bath that is at fault but whatever is around it. I know what follows is a long shot, but it's the only I can come up with at the moment:

On the circuit, there is some equipment (towel rail or washing machine, maybe?) with capacitive coupling to earth or poor insulation leading to a slight current trying to find its way back via the circuit protective conductor. However, the cpc of the circuit has somehow been broken. This means that the equipment and possible the surrounding area are live with respect to properly bonded objects, like the bath. Thus the tingle.

When the bath is plugged into the circuit, the circuit becomes bonded/earthed through the cord to the bath. This eliminates the potential between the bath and whatever is connected on the circuit.

{Edit for lack of grammar}

[This message has been edited by C-H (edited 01-21-2005).]

the waste is plastic,, it discharges into a normal grid and doesnt even touch it.
all neutrals are tight,

the only soultion i could think of is there is a supply company pole a few yards from the house which has an earth stake,(pme) i have asked them to check it out just in case there is current flowing down here into the ground, then when you empty the bath you will get a connection to earth via the person pulling the plug and the water running into the drain.. the bath is enammeld so probably no earth connection through that,

it is very worrying,

Certainly a head-scratcher!

You mentioned a PME ground rods on a nearby pole, but is the house actually connected as PME or is it TN-S or TT ?

hi Paul
yep its TNC-S (pme) and connected in the house as that..

something i forgot to mention which as a long shot.. there is a 2.5 swa going to the stables over 100mtrs away. i have the problem that the cable full of capacitance, something i am waiting for the ECA to come back to me with regard to getting it discharged. never thought about that.. C+H mentioned capacitance in a machine, now would or could this have a bearing on things... ie the path via the bath having the least resistance?? when it discharges.. the cold main enters the house under the bath, solid floor, so effectivley the ground around the pipe would be live, and when the water leaves the bath as you pull the plug you get a small current flowing through you???

Long shot???? thoughts..

PaulC,
Shouldn't the Armouring in the SWA cable be at Earth potential?.
I would have thought that this would tend to drain away any Capacitive effects from within the cable.
Is the Cold water main actually buried before it enters the house, if it is, that should also be at Earth potential.
Are the hot and cold water systems bonded together?, I have seen Elements leak current into the pipework, before today and it is usually the sign of an imminent element failure, however the current is too low to trip any RCD protection.
Only other thing I can come up with is:
Is the house on one single RCD or a couple of them?.
One thing I have come across before is where an "RCD neutral" was connected to the wrong Neutral busbar in the switchboard, referencing it back to the Mains earth, this in turn, causes tingles at poorly earthed fittings.
Other than that, I'm empty!.

I can't see the capacitance in the SWA feeder being the culprit so long as everything is securely bonded.

If the feeder insulation was damaged and you had a leak in the drainage system, you might get some leakage into the water. Or maybe if just the outer sheath was damaged and the armor wasn't grounded (I see that a lot) then the capacitance could be enough to give some leakage current into the water. Either way, that could be checked easily by cutting power to the feeder.

Are there any other feeds underground near the drain which could have gone faulty, such as the main to the house? Just a thought.

Just one other point to clarify: When somebody gets a tingle as the water is running away, is this while still sitting in the tub, or while standing on the bathroom floor and touching it?

pme is probably the problem. this is the result of small diverted neutral currents causing perceived shock. It is a relatively well documented phenomenon that people showering in leisure complexes connected to pme earths often feel a tingling sensation. It is often cured by ensuring that a metal floor grid is installed which is connected to the local supplementary bonding arrangements. Many designers will ensure that such facilities are not connected to a pme terminal but are TN-S or TT.
I take it that Paul is right when he assumes the water is flowing and the client is touching the bath while standing on the floor.
I should also say dont discount other possibilities. Remember a spark a few years ago got six months for negligence in just such a situation. A girl was electrocuted at a kitchen sink after reporting shocks as she used the kitchen sink. Poor old sparky investigated but was beat and put it down to static. It turned out that there was an intermittent earth fault om central heating timer. So I give my diagnosis only by way of technical chat and suggest that you dont let the matter go unresolved! Good luck!

[This message has been edited by lyledunn (edited 01-23-2005).]

[This message has been edited by lyledunn (edited 01-23-2005).]

Non expert opinion... but i'd suggest running a flow of salty water down the plug hole and using a sensitive meter check for small currents. (taking precautions to avoid any shock incase it is a major fault!)

With co-operation from any neighbouring houses etc.. shut everything off and then co-ordinate switching them back on again bit by bit until you find the problem.

Should you perhaps get the Power Company involved as it could be a PME failure?
They usually have someone who's expert in solving these problems at hand!

Good point Dave -- Could be a failed or bad neutral on the PoCo lines.

Didn't see it mentioned, (Yep, someone did mention it.) but have you isolated the circuit this current is from? Like by shutting things off. i.e. circuit off, no current, and vice versa. Just to locate the source. ( Or whole house off, its outside. ) Then you can break up that circuit in sections to isolate further. Then, and I'm not sure you can do this with some of the ring methods used in other than the US. But you might be able to pin-point further with a graphic TDR.

[This message has been edited by e57 (edited 01-23-2005).]

Sorry, just to be clear I didnt think water had anything to do with it from even a failed neutral point of view given the high resistance of water even the most contaminated sort! I thought perhaps that water down plug hole and voltage were just co-incidental. I cant see how any potential could be introduced by reading the post. However, if leaking waste making contact with some live part then perhaps that is a different matter. Please let us know outcome!

Fresh water's not very conductive, but you can never be sure what electrolytic substances people may add to their bathwater!

Well Thanks Guys,

I have instructed the power company to investigate the pole..
Trumpy.. yep all pipes and bath are at earth potential. though as i have said before there is a good chance that the enamell on the bath would increase the resistance to earth..the house is on one RCD..yep the water is buried and comes up under the bath..
good point the on the SWA the sheath is not earthed and is on my inspection report, would this stop the capacitance??

Paul UK.. they only get the tingle when outside the bath and pulling the plug, its as if the connection is made when the water hits the drain...no other cables buried that i know of, the supply is overhead..

Lyle.. yep i know mate it is a worry, i need to resolve this pretty quick.. they had a spark do some work there, before me and since he has been there this has been happening, but i cant come up with what he has done to cause this,, but looking at his work i told the client that there is no way he was a spark, he had done things a spark would,nt have done.even a rough one..

E57.. hi cant isolate any circuit because the fault is intermitant..they ring me i go out and pull the plug, nothing..

just waiting for the outcome of the power company..
if some one could confirm the earthing of the swa sheath would discharge the capacitance..
cheers guys,

Paul,
What's on the end of that Submain feed cable?.
Is there a possibility that someone could have driven an Earth stake at the other end?.
I'm just wondering if there isn't some sort of a circulating earth current here, between the Main earthing of the house and the barn.
How many cores does the SWA have?.
Are there any Electric fence systems near the house?.
It wouldn't be the first time a farmer has driven a fence earth through a pipe and not realised.

Hi Trumpy

no earth stakes on site, the swa sub main to the barn is a 3 core.the barn is 100 mtrs away so i would doubt that would have any effect anyway..

not sure about any electric fence though..

Hi Paul,
Just to clarify something, with regard to when the plug is pulled, does it only happen if they are simultaneously touching the bath itself, or just standing on the floor

UPDATE on the live bath..

Western Power came to site tonight to survey the pole,, found 18volts entering the ground around my customers house..

when he pulled the plug and the water hit the drain, bingo earth path made via the bathee.( is there such a word??)

they say it looks like a faulty neutral earth connection in one of the neighbours house's...(all PME around there) also just heard that one of them is a diy freak...

phewwww can sleep tonight,

will post the full report soon..

Cool,
I'm certainly glad that that has been solved!.
It's strange how a system that is installed to protect people against shock can cause a thing like this to happen.

Indeed. Makes you wonder whether the recommended (or required-by-code) approach is always the best, doesn't it?

You would have appreciated some of the discussions I had with Bennie Palmer a couple of years ago. We exchanged a good many messages on the subject of bonding vs. isolation and grounding issues.

how did they measure this`?

Cant see this for the life of me! I would be amazed if bath water in waste could introduce earth potential, or any other potential for that matter. A 1m column of water with a high degree of disolved salts in a 15mm plastic pipe will have a resistance of circa 30,000 ohms! I can see however, that a poor neutral connection in neighbouring premises would increase potential between bonded bath and floor, which may be more representative of true earth. May be reasonable to sink spike to reduce touch voltages on pme systems where neutral problems will always exist.